Overheating (with a twist)
Discussion
Hi All,
I have what seems to be the usual overheating problem when I run the car on a hot day or I get caught in traffic the needle edges into the red. On a cool day it will run fine for hours. This is a new problem and I've had the car running fine for years.
I assumed faulty thermostat so I've just finished dismantling the housing to find a previous owner has completely removed it. There's just an empty hole where the thermostat should be.
Both fans come on at 90 and are working fine. I've checked the oil and there's no sign of cross-contamination. Also no oil in the drained coolant.
Car is an unmodified 430 pre-cat with an alloy radiator. It had a full rebuild 3 years ago. The water pump is clearly working as I can see water flowing into the swirl pot.
Any thoughts would be very gratefully received. My top idea is a radiator blockage but is there any way to clear this without removing the radiator?
I have a new thermostat, would you refit it given this is a summer only car? The car heats up pretty quickly without it any way.
Cheers,
Simon
I have what seems to be the usual overheating problem when I run the car on a hot day or I get caught in traffic the needle edges into the red. On a cool day it will run fine for hours. This is a new problem and I've had the car running fine for years.
I assumed faulty thermostat so I've just finished dismantling the housing to find a previous owner has completely removed it. There's just an empty hole where the thermostat should be.
Both fans come on at 90 and are working fine. I've checked the oil and there's no sign of cross-contamination. Also no oil in the drained coolant.
Car is an unmodified 430 pre-cat with an alloy radiator. It had a full rebuild 3 years ago. The water pump is clearly working as I can see water flowing into the swirl pot.
Any thoughts would be very gratefully received. My top idea is a radiator blockage but is there any way to clear this without removing the radiator?
I have a new thermostat, would you refit it given this is a summer only car? The car heats up pretty quickly without it any way.
Cheers,
Simon
I would put a thermostat in, the pump needs some 'resistance' to avoid air-locks.....
No kinked/collapsed hoses, air-channels in the rad clear of crud ?
If you refill, open the bleed nut (top O/S of rad) and then take off the hose on top of the pump feed and fill (funnel of 10 mm needed) then run the engine and let it 'burp' for a few minutes
No kinked/collapsed hoses, air-channels in the rad clear of crud ?
If you refill, open the bleed nut (top O/S of rad) and then take off the hose on top of the pump feed and fill (funnel of 10 mm needed) then run the engine and let it 'burp' for a few minutes
Its a simple battle between your fans, radiator efficiency, and the rise in engine coolant temperature; on a cool day the fans will win, but a hot day it sounds like your fans are proving themselves to be fractionally inadequate. Your fans only need to be performing slightly below par to cause a problem in this really hot weather, over the years the fan wiring gets tired and the fan earths become corroded, the consequence is the fans may be running on a reduced current supply and so running a little slow.
Add this to some inevitable wear in the fan motors themselves and the fans may not be pulling enough air through the rad to win the battle, if the rad is old and its fins are full of flys it will only add to the problem. On a cool day the fans and rad setup may well be sufficient to bring the coolant temp down from a design peak of 92 degrees, but on a hot day a marginal fan & rad will mean temperatures will keep climbing slowly... degree by degree.
If you suspect the above a good test is leave the car idling until the temp creeps up to 95, then spray the rad with a garden hose, if the temp falls (and it almost certainly will), you can safely assume its fan/rad related. The rad is just a heat exchanger and the fans are there to help, the rad and fans were fine when new but TVR didn't build in much of a safety margin so even a small current drop to the fans from something like a corroded earth is often enough to allow slow thermal runaway.
Add this to some inevitable wear in the fan motors themselves and the fans may not be pulling enough air through the rad to win the battle, if the rad is old and its fins are full of flys it will only add to the problem. On a cool day the fans and rad setup may well be sufficient to bring the coolant temp down from a design peak of 92 degrees, but on a hot day a marginal fan & rad will mean temperatures will keep climbing slowly... degree by degree.
If you suspect the above a good test is leave the car idling until the temp creeps up to 95, then spray the rad with a garden hose, if the temp falls (and it almost certainly will), you can safely assume its fan/rad related. The rad is just a heat exchanger and the fans are there to help, the rad and fans were fine when new but TVR didn't build in much of a safety margin so even a small current drop to the fans from something like a corroded earth is often enough to allow slow thermal runaway.
I have to agree with the comment a few above as it looks to me as if the previous owner took out the thermostat in an attempt to get around an overheating issue.
If the engine heats up quickly without a thermostat fitted then it suggests an air lock or blockage somewhere. My experience is that if you run with a thermostat that is permanently open (or missing), the engine takes an age to reach its normal operating temperature, if ever in colder weather.
If the problem is an airlock you can usually tell by simply squeezing the hose above the thermostat when cold to establish if coolant or air is in the hose. If a blockage, the most likely culprit is a sludged up radiator, possibly as a result of an additive such as rad-weld restricting flow. Empting and back flushing should help diagnosis.
If the engine heats up quickly without a thermostat fitted then it suggests an air lock or blockage somewhere. My experience is that if you run with a thermostat that is permanently open (or missing), the engine takes an age to reach its normal operating temperature, if ever in colder weather.
If the problem is an airlock you can usually tell by simply squeezing the hose above the thermostat when cold to establish if coolant or air is in the hose. If a blockage, the most likely culprit is a sludged up radiator, possibly as a result of an additive such as rad-weld restricting flow. Empting and back flushing should help diagnosis.
Thanks for all your replies. I think I will put a thermostat in as I don't like the idea of not having one. Steve Heath talks about drilling a few holes in it to prevent "thermal shock" and allow a small amount of water out to the rad even when cold. Has anyone done this on their car?
I've bought one of those laser thermometers to see if I can work out if there's an air lock forming somewhere or a blockage in the radiator. Plus it looks like a fun gadget.
On the fans, one of them failed last year (seized solid) and I thought originally that was the source of the problem but there's a brand new one in now and I still have the same problem. What's the best method to test if the fans are running at maximum efficiency? I rebuilt the car 3 years ago and cleaned up all the earths then; but the wiring is old now and has been in a very hot environment so may not be work at its best.
I'll post back when I have it all reassembled and see.
Cheers,
Simon
I've bought one of those laser thermometers to see if I can work out if there's an air lock forming somewhere or a blockage in the radiator. Plus it looks like a fun gadget.
On the fans, one of them failed last year (seized solid) and I thought originally that was the source of the problem but there's a brand new one in now and I still have the same problem. What's the best method to test if the fans are running at maximum efficiency? I rebuilt the car 3 years ago and cleaned up all the earths then; but the wiring is old now and has been in a very hot environment so may not be work at its best.
I'll post back when I have it all reassembled and see.
Cheers,
Simon
cavebloke said:
Thanks for all your replies. I think I will put a thermostat in as I don't like the idea of not having one. Steve Heath talks about drilling a few holes in it to prevent "thermal shock" and allow a small amount of water out to the rad even when cold. Has anyone done this on their car?
I've bought one of those laser thermometers to see if I can work out if there's an air lock forming somewhere or a blockage in the radiator. Plus it looks like a fun gadget.
On the fans, one of them failed last year (seized solid) and I thought originally that was the source of the problem but there's a brand new one in now and I still have the same problem. What's the best method to test if the fans are running at maximum efficiency? I rebuilt the car 3 years ago and cleaned up all the earths then; but the wiring is old now and has been in a very hot environment so may not be work at its best.
I'll post back when I have it all reassembled and see.
Cheers,
Simon
You can check the fans are performing as they should be by connecting them with good twin cable one at a time to a known good fully charged battery and by placing a Ammeter in series with the positive supply measure their current consumption, if the fans are identical they should both draw very close to the same current, you can now contact the manufacturer of your fan motors requesting their current draw figures and compare these figures with your findings I've bought one of those laser thermometers to see if I can work out if there's an air lock forming somewhere or a blockage in the radiator. Plus it looks like a fun gadget.
On the fans, one of them failed last year (seized solid) and I thought originally that was the source of the problem but there's a brand new one in now and I still have the same problem. What's the best method to test if the fans are running at maximum efficiency? I rebuilt the car 3 years ago and cleaned up all the earths then; but the wiring is old now and has been in a very hot environment so may not be work at its best.
I'll post back when I have it all reassembled and see.
Cheers,
Simon
Removing the thermostat to resolve an overheating issue is the work of the retarded for two very god reasons, the first being the thermostat is only there to aid faster warm up, it has no bearing on the efficiency of the cooling system. With the thermostat removed the car will take longer to warm up but the coolant will still eventually reach the peak temperature, because this is dictated by the cooling system capacity and efficiency... not the thermostat!
Secondly removing the thermostat may indeed worsen an overheating condition because the system is designed to operate with a thermostat in place, as the hot coolant leaves the cylinder head it must pass through the smaller diameter thermostat, this creates a venturi effect speeding up water flow at this critical point in the engine so improving the evacuation of hot coolant from the cylinder head where engine heat is created.
Remove the thermostat and you remove the venturi effect, the engine will take longer to warm up without the thermostat in place but as the coolant reaches the peak design temperature dictated by the cooling system capacity and efficiency thermal runaway will be faster than if you'd just left the thermostat where it was designed to be.
If the rad is blocked internally with corrosion or Radweld, or eternally with road debris and insects it will no longer be working to it's designed efficiency, your rad is just a heat exchanger so relys on both the efficient flow of coolant and a ready supply of moving air to perform as designed. If the fans aren't receiving their full serving of amps due to old corroded wiring and earth points (very common on TVRs) they will run slow. If the fans are the originals they will be some 20 years or more old, as the motors wear they become less efficient so again they will run slow, slow fans create less of this essential airflow and this may well be just enough to push the cooling system beyond its design limits!
If you have one or maybe two of the above issues there's probably enough head-space designed into the system to cope, what I suspect the OP is suffering from is a combination of all of the above, ie the rad is partially blocked internally, partially blocked externally and the fans are running a bit slower than designed due to corroded connectors and or poor earths. In cooler ambient temps the problem does not present itself, but as soon as the car is expected to function in this hotter weather the OP is reaching the tipping point and slow thermal runaway is the consequence.
Thermal runaway is the uncontrolled rise of temperature, this needn't be rapid as you might assume, indeed is often a very slow but progressive process as the rad and fans and rad efficiency are fractionally falling behind in the battle to control the natural effect of the coolant temp continuing to rise if left un-managed.
If I was the OP I'd do the following:
1. Remove the rad and back flush it
2. Clean the rad fins of insects and road debris
3. Check and clean the fan earth points and it's connectors, all of which corrode badly on these cars causing significant current drops and slow running fans
4. Replace the thermostat if missing or test if in place, these engines were designed to run an 88 degree thermostat, the use of a cooler thermostat will not help an underlying issue with your cooling system so fitting one is pointless, if the car overheats with the correct 88 degree thermostat something is wrong with your cooling system, the solution is not to fit a lower value thermostat!
5. Optional: Replace both fans with new units from Spal, the latest offering from Spal that shifts a bit more air and is longer lasting than the original used by TVR is VA10-AP70/LL-61A and costs £132.00 each including VAT & delivery if you buy direct from Spal (Call Maggie on 01905 613714 Ext. 206)
If your rad is clear internally and externally and your fans are running at full speed your TVR fitted with the correct 88 degree thermostat will not overheat.... even at idle in the very hottest weather!
Secondly removing the thermostat may indeed worsen an overheating condition because the system is designed to operate with a thermostat in place, as the hot coolant leaves the cylinder head it must pass through the smaller diameter thermostat, this creates a venturi effect speeding up water flow at this critical point in the engine so improving the evacuation of hot coolant from the cylinder head where engine heat is created.
Remove the thermostat and you remove the venturi effect, the engine will take longer to warm up without the thermostat in place but as the coolant reaches the peak design temperature dictated by the cooling system capacity and efficiency thermal runaway will be faster than if you'd just left the thermostat where it was designed to be.
If the rad is blocked internally with corrosion or Radweld, or eternally with road debris and insects it will no longer be working to it's designed efficiency, your rad is just a heat exchanger so relys on both the efficient flow of coolant and a ready supply of moving air to perform as designed. If the fans aren't receiving their full serving of amps due to old corroded wiring and earth points (very common on TVRs) they will run slow. If the fans are the originals they will be some 20 years or more old, as the motors wear they become less efficient so again they will run slow, slow fans create less of this essential airflow and this may well be just enough to push the cooling system beyond its design limits!
If you have one or maybe two of the above issues there's probably enough head-space designed into the system to cope, what I suspect the OP is suffering from is a combination of all of the above, ie the rad is partially blocked internally, partially blocked externally and the fans are running a bit slower than designed due to corroded connectors and or poor earths. In cooler ambient temps the problem does not present itself, but as soon as the car is expected to function in this hotter weather the OP is reaching the tipping point and slow thermal runaway is the consequence.
Thermal runaway is the uncontrolled rise of temperature, this needn't be rapid as you might assume, indeed is often a very slow but progressive process as the rad and fans and rad efficiency are fractionally falling behind in the battle to control the natural effect of the coolant temp continuing to rise if left un-managed.
If I was the OP I'd do the following:
1. Remove the rad and back flush it
2. Clean the rad fins of insects and road debris
3. Check and clean the fan earth points and it's connectors, all of which corrode badly on these cars causing significant current drops and slow running fans
4. Replace the thermostat if missing or test if in place, these engines were designed to run an 88 degree thermostat, the use of a cooler thermostat will not help an underlying issue with your cooling system so fitting one is pointless, if the car overheats with the correct 88 degree thermostat something is wrong with your cooling system, the solution is not to fit a lower value thermostat!
5. Optional: Replace both fans with new units from Spal, the latest offering from Spal that shifts a bit more air and is longer lasting than the original used by TVR is VA10-AP70/LL-61A and costs £132.00 each including VAT & delivery if you buy direct from Spal (Call Maggie on 01905 613714 Ext. 206)
If your rad is clear internally and externally and your fans are running at full speed your TVR fitted with the correct 88 degree thermostat will not overheat.... even at idle in the very hottest weather!
ChimpOnGas said:
If I was the OP I'd do the following:
1. Remove the rad and back flush it
2. Clean the rad fins of insects and road debris
3. Check and clean the fan earth points and it's connectors, all of which corrode badly on these cars causing significant current drops and slow running fans
4. Replace the thermostat if missing or test if in place, these engines were designed to run an 88 degree thermostat, the use of a cooler thermostat will not help an underlying issue with your cooling system so fitting one is pointless, if the car overheats with the correct 88 degree thermostat something is wrong with your cooling system, the solution is not to fit a lower value thermostat!
5. Optional: Replace both fans with new units from Spal, the latest offering from Spal that shifts a bit more air and is longer lasting than the original used by TVR is VA10-AP70/LL-61A and costs £132.00 each including VAT & delivery if you buy direct from Spal (Call Maggie on 01905 613714 Ext. 206)
Thanks for taking the time to give me a plan of action - it all sounds like sage advice to me. I've just got to make the time to get on with it now.1. Remove the rad and back flush it
2. Clean the rad fins of insects and road debris
3. Check and clean the fan earth points and it's connectors, all of which corrode badly on these cars causing significant current drops and slow running fans
4. Replace the thermostat if missing or test if in place, these engines were designed to run an 88 degree thermostat, the use of a cooler thermostat will not help an underlying issue with your cooling system so fitting one is pointless, if the car overheats with the correct 88 degree thermostat something is wrong with your cooling system, the solution is not to fit a lower value thermostat!
5. Optional: Replace both fans with new units from Spal, the latest offering from Spal that shifts a bit more air and is longer lasting than the original used by TVR is VA10-AP70/LL-61A and costs £132.00 each including VAT & delivery if you buy direct from Spal (Call Maggie on 01905 613714 Ext. 206)
Do you think I need to remove the rad to back flush it? Would there be any issues with doing it in place if I control the exit water flow using some old piping?
Cheers,
Simon
Penelope Stopit said:
You can check the fans are performing as they should be by connecting them with good twin cable one at a time to a known good fully charged battery and by placing a Ammeter in series with the positive supply measure their current consumption, if the fans are identical they should both draw very close to the same current, you can now contact the manufacturer of your fan motors requesting their current draw figures and compare these figures with your findings
I thought I better post this information again as I am worried that you have missed itcavebloke said:
ChimpOnGas said:
If I was the OP I'd do the following:
1. Remove the rad and back flush it
2. Clean the rad fins of insects and road debris
3. Check and clean the fan earth points and it's connectors, all of which corrode badly on these cars causing significant current drops and slow running fans
4. Replace the thermostat if missing or test if in place, these engines were designed to run an 88 degree thermostat, the use of a cooler thermostat will not help an underlying issue with your cooling system so fitting one is pointless, if the car overheats with the correct 88 degree thermostat something is wrong with your cooling system, the solution is not to fit a lower value thermostat!
5. Optional: Replace both fans with new units from Spal, the latest offering from Spal that shifts a bit more air and is longer lasting than the original used by TVR is VA10-AP70/LL-61A and costs £132.00 each including VAT & delivery if you buy direct from Spal (Call Maggie on 01905 613714 Ext. 206)
Thanks for taking the time to give me a plan of action - it all sounds like sage advice to me. I've just got to make the time to get on with it now.1. Remove the rad and back flush it
2. Clean the rad fins of insects and road debris
3. Check and clean the fan earth points and it's connectors, all of which corrode badly on these cars causing significant current drops and slow running fans
4. Replace the thermostat if missing or test if in place, these engines were designed to run an 88 degree thermostat, the use of a cooler thermostat will not help an underlying issue with your cooling system so fitting one is pointless, if the car overheats with the correct 88 degree thermostat something is wrong with your cooling system, the solution is not to fit a lower value thermostat!
5. Optional: Replace both fans with new units from Spal, the latest offering from Spal that shifts a bit more air and is longer lasting than the original used by TVR is VA10-AP70/LL-61A and costs £132.00 each including VAT & delivery if you buy direct from Spal (Call Maggie on 01905 613714 Ext. 206)
Do you think I need to remove the rad to back flush it? Would there be any issues with doing it in place if I control the exit water flow using some old piping?
Cheers,
Simon
Diagnosis of the current drawn by your fans is your best starting point though, a for this an inexpensive inductive clamp meter is your best friend, £22.00 buys you a cheap one that works just fine and will prove an invaluable tool for future TVR electrical diagnostics.
http://www.ebay.co.uk/itm/UNI-T-UT203-Digital-Hand...
Each fan should draw roughly 14.2 amps when running though you should expect to see a much higher figure (spike) momentarily on startup.
Penelope Stopit said:
I thought I better post this information again as I am worried that you have missed it
Thanks for this. I've added this to my list and particularly after reading carsy's old thread. I have a multimeter already so I will set to work on trying to figure out the problem. This may be the most likely thing now as the rad is a new-ish alloy one, so it's not that likely to be blocked with crud (I will check and back-flush though).Simon
cavebloke said:
Penelope Stopit said:
I thought I better post this information again as I am worried that you have missed it
Thanks for this. I've added this to my list and particularly after reading carsy's old thread. I have a multimeter already so I will set to work on trying to figure out the problem. This may be the most likely thing now as the rad is a new-ish alloy one, so it's not that likely to be blocked with crud (I will check and back-flush though).Simon
ChimpOnGas said:
5. Optional: Replace both fans with new units from Spal, the latest offering from Spal that shifts a bit more air and is longer lasting than the original used by TVR is VA10-AP70/LL-61A and costs £132.00 each including VAT & delivery if you buy direct from Spal (Call Maggie on 01905 613714 Ext. 206)
If your rad is clear internally and externally and your fans are running at full speed your TVR fitted with the correct 88 degree thermostat will not overheat.... even at idle in the very hottest weather!
Some great advice here from CoG. I went with these SPAL fans too, and OMG what a difference. And I am running the car in the very hottest weather. No issues now.If your rad is clear internally and externally and your fans are running at full speed your TVR fitted with the correct 88 degree thermostat will not overheat.... even at idle in the very hottest weather!
One other point I don't think was mentioned - the wiring and relays fuses back in the cabin. On my 94 pre-serp 500, I had two fans supplied through one relay and fuse. The famous 40A unit...
Due to that and other marginal effects (including the connectors etc) the fans would not run at good enough speed - too much voltage drop from running through one supply. Was like an asthmatic pensioner breathing across the rad...
If you have space on the fuse board, it is worth splitting the supply (2 x 25A fuses and relays) - which was fixed in the later Serp models. Doesn't fix all the other good stuff quoted above (flush, connectors and thermostat etc), but worth checking the wiring before you buy those new fans... There may be nothing wrong with them.
Due to that and other marginal effects (including the connectors etc) the fans would not run at good enough speed - too much voltage drop from running through one supply. Was like an asthmatic pensioner breathing across the rad...
If you have space on the fuse board, it is worth splitting the supply (2 x 25A fuses and relays) - which was fixed in the later Serp models. Doesn't fix all the other good stuff quoted above (flush, connectors and thermostat etc), but worth checking the wiring before you buy those new fans... There may be nothing wrong with them.
My griff has just been put back on the road after a prolonghed absence with new radiator, coolant flush etc and while mine wasn't overheating in town it was running on motorways with the fans constantly on.
I decided to get one of those front diffusers from TVR parts and fitted it - absolutely no probs now - runs on motorway at speed, no fans on and needle in the middle of the gauge.
If you look at the angle of the radiator in the Griffith it's at such a funny angle and the vent on a precat is so small that it's a wonder the radiator can work at all compared to the more upright position on the Chimaera.
I'm not sure how it will fare with speed humps but not only does it run cooler but it feels way more stable on the motorway now too...
Saxon
I decided to get one of those front diffusers from TVR parts and fitted it - absolutely no probs now - runs on motorway at speed, no fans on and needle in the middle of the gauge.
If you look at the angle of the radiator in the Griffith it's at such a funny angle and the vent on a precat is so small that it's a wonder the radiator can work at all compared to the more upright position on the Chimaera.
I'm not sure how it will fare with speed humps but not only does it run cooler but it feels way more stable on the motorway now too...
Saxon
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