Cooling System Pressure
Discussion
What pressure is the 4.2 cooling system meant to run at? I've had problems with serious overheating due to loss of coolant (or maybe vice versa)
I've bled the system, but it's still losing water somewhere.
I've justed tested the system with a pressure tester - the system on the car holds 15psi for 30 minutes, doesn't move a bit, so I'm sure that's ok. Might be different if the system's hot I suppose but the instructions say only use the tester on a cold engine.
The cap is losing pressure very slowly - dropping from 15psi to 14 over 30 minutes or so, but that might be an air loss in the tester adaptor. What I did notice though is that I have to screw the cap on REALLY tight or it loses pressure a lot quicker - drops to 10psi in the same time. I mean as tight as your wee hands can turn it, or it loses pressure.
I think the cap is shot but I don't know what pressure it's meant to keep. Probably worth changing anyway.
I've bled the system, but it's still losing water somewhere.
I've justed tested the system with a pressure tester - the system on the car holds 15psi for 30 minutes, doesn't move a bit, so I'm sure that's ok. Might be different if the system's hot I suppose but the instructions say only use the tester on a cold engine.
The cap is losing pressure very slowly - dropping from 15psi to 14 over 30 minutes or so, but that might be an air loss in the tester adaptor. What I did notice though is that I have to screw the cap on REALLY tight or it loses pressure a lot quicker - drops to 10psi in the same time. I mean as tight as your wee hands can turn it, or it loses pressure.
I think the cap is shot but I don't know what pressure it's meant to keep. Probably worth changing anyway.
GreenV8S said:
I don't know what the spec is on the Cerbera specifically, 15 psi is more or less universal.
Yes Peter that's what I reckoned when I was testing earlier. I've checked the VW spec and it is 15 right enough.Tried the car tonight with the pressure cap screwed down dead tight. Rose to 85 degrees or so then dropped as the thermostat opened, back up to just below 90 degrees and fans cut in, cooled car to just below 85 and fans went off. Let it repeat that cycle, seems to be exactly to spec.
No explanation why it's been overheating... I'll try it on the road at the weekend.
That cap shouldn't need to be tightened within an inch of its life in order to hold pressure. I suggest you check the face that it is sealing against, and replace the cap. Also see if there are signs of weaping around the cap. You won't see the water, but there would be signs of dried antifreeze.
This is driving me mental...
The Cerb is still overheating, I think mainly in traffic. It runs fine, motors about at just over 80 degrees, temp increases to just below 90, fans cut in, temp drops, fans go off at 83. (It's got a TCS chip). So far so good,
But if you stop or slow in traffic, the temp creeps up to 90. Then a couple of times later, well over 90. Maybe 20 miles or so, get home, switch off, check coolant level next day when engine is cold and coolant tank is nearly empty.
It's clearly coming out of the cap - that are is soaking in coolant. But I thinks that's BECAUSE of the overheating, not the cause of it.
Here's where I am now:
Pressure test as above, shows the system maintains pressure.
New coolant cap fitted - still the same.
Antifreeze mix too weak so drained and advance antifreeze "protects against overheating to 130 degrees" put in - still the same.
New antifreeze is bright orange / pink so spillages and leaks are obvious!
System bled and bled and bled as per the manual - but every time I check it, there's air in there. Not much, but some.
Needle occasionally "flicks" as capillary systems do if there's air in there.
Am I missing something on the bleeding? Is there another "trick" that's not in the manual procedure?
I want to fit a manual switch, apparently you have to earth pins 6 and 41 on the ecu - I can't see how to get to the terminals to do that. I think I would be better grounding the relays but I can't figure out how.
Any advice?
TIA
The Cerb is still overheating, I think mainly in traffic. It runs fine, motors about at just over 80 degrees, temp increases to just below 90, fans cut in, temp drops, fans go off at 83. (It's got a TCS chip). So far so good,
But if you stop or slow in traffic, the temp creeps up to 90. Then a couple of times later, well over 90. Maybe 20 miles or so, get home, switch off, check coolant level next day when engine is cold and coolant tank is nearly empty.
It's clearly coming out of the cap - that are is soaking in coolant. But I thinks that's BECAUSE of the overheating, not the cause of it.
Here's where I am now:
Pressure test as above, shows the system maintains pressure.
New coolant cap fitted - still the same.
Antifreeze mix too weak so drained and advance antifreeze "protects against overheating to 130 degrees" put in - still the same.
New antifreeze is bright orange / pink so spillages and leaks are obvious!
System bled and bled and bled as per the manual - but every time I check it, there's air in there. Not much, but some.
Needle occasionally "flicks" as capillary systems do if there's air in there.
Am I missing something on the bleeding? Is there another "trick" that's not in the manual procedure?
I want to fit a manual switch, apparently you have to earth pins 6 and 41 on the ecu - I can't see how to get to the terminals to do that. I think I would be better grounding the relays but I can't figure out how.
Any advice?
TIA
ro_butler said:
Do a test to see if there are any hydrocarbons in the coolant, which might be a symptom of a head gasket failure. It could explain the overheating and the extra air that seems to 'appear' in the system even after bleeding.
I always like to exhaust the quick and cheap tests first.
Go to the top of the class!!!I always like to exhaust the quick and cheap tests first.
When I read your post it all made sense - the car's behaviour is symptomatic of mild head gasket failure. For example, a couple of times it's heated up going up a hill but cooled going down the other side.
It was your bit about air appearing in the system that hit the spot though, so carried out a hydrocarbon sniffer test tonight on the header tank - and the fluid didn't turn yellow, but it went green right in the last 3 or 4 seconds of the minute long test - if it had taken just a few seconds longer I wouldn't have noticed it. But definitely hydrocarbybuggers in the cooling system.
I didn't bother doing other tests to narrow it down (ie pulling off leads one at a time to see which cylinder it might be) because it's either all right, or it's not. And it's not.
So that's it then.
Any idea how much I should ask granny to send me by postal order to cover the repair cost?
tvrgit said:
ro_butler said:
Do a test to see if there are any hydrocarbons in the coolant, which might be a symptom of a head gasket failure. It could explain the overheating and the extra air that seems to 'appear' in the system even after bleeding.
I always like to exhaust the quick and cheap tests first.
Go to the top of the class!!!I always like to exhaust the quick and cheap tests first.
When I read your post it all made sense - the car's behaviour is symptomatic of mild head gasket failure. For example, a couple of times it's heated up going up a hill but cooled going down the other side.
It was your bit about air appearing in the system that hit the spot though, so carried out a hydrocarbon sniffer test tonight on the header tank - and the fluid didn't turn yellow, but it went green right in the last 3 or 4 seconds of the minute long test - if it had taken just a few seconds longer I wouldn't have noticed it. But definitely hydrocarbybuggers in the cooling system.
I didn't bother doing other tests to narrow it down (ie pulling off leads one at a time to see which cylinder it might be) because it's either all right, or it's not. And it's not.
So that's it then.
Any idea how much I should ask granny to send me by postal order to cover the repair cost?
Further update:
Contacted the local TVR specialist a couple of days after my last post here, who said that it did sound like mild head gasket failure but he doesn't do AJP8 engines so I'd have to take it elsewhere - not any old elsewhere but one specific elsewhere who I think is well respected on here.
BUT! he said, before you do, try a coolant sealer - the leak sounds very mild and a good sealer should fix it. "What have you got to lose?" he said.
So I bought some, put it in, drove about and it's better, definitely. But it still overheats.
It's fine when motoring along at reasonable speeds. It's fine when stationary when the fans kick in exactly when they should. But moving at lowspeed, it gets hot... if you stop at traffic lights when it's too hot, it cools down... then if you drive away slow, it heats up again... but if you blast off, it cools down more...
So... more tests. Another pressure test (cold) shows it holds it's pressure easily. Another hydrocarbon test shows nothing, after 5 minutes (last time it changed at 1 minute, the standard test time).
I think I might be overfilling it so I've tried putting less water in - symptoms exactly the same.
What I did notice though (prompted largely by an email from another PHer, thanks John) was that there is hardly any radiator exposed to direct air flow. I took a pic and shaded bits for clarity:
The red bits are the oil cooler. The white bit is the number plate, obviously. The yellow bits are the only bits of the radiator you can see from head-on - the intake air scoop takes up nearly all the space above the plate.
My reckoning is: at high speeds the ram-effect pushes air through the radiator. At idle, the fans can suck enough air through to stabilise the temperature. When moving slowly though, the engine is generating slightly more heat, more than the fans can cope with, and there's no ram-effect so the radiator isn't working properly.
So next step is: clean through the radiator fins with a jet wash, then try taking the number plate off, and then if necessary, leave the fans on all the time.
I just this minute thought of something else - if the fan is wired up to turn the wrong way, it'll work ok when fast because there's enough air getting forced through. It'll work when stationary even if the fan is blowing instead of sucking. But if moving slowly, the fan is trying to blow air one way while the car is generating a gentle breeze in the other direction, so the air won't actually move through the radiator fins at all. Another thing to check!
It's driving me mental...
Contacted the local TVR specialist a couple of days after my last post here, who said that it did sound like mild head gasket failure but he doesn't do AJP8 engines so I'd have to take it elsewhere - not any old elsewhere but one specific elsewhere who I think is well respected on here.
BUT! he said, before you do, try a coolant sealer - the leak sounds very mild and a good sealer should fix it. "What have you got to lose?" he said.
So I bought some, put it in, drove about and it's better, definitely. But it still overheats.
It's fine when motoring along at reasonable speeds. It's fine when stationary when the fans kick in exactly when they should. But moving at lowspeed, it gets hot... if you stop at traffic lights when it's too hot, it cools down... then if you drive away slow, it heats up again... but if you blast off, it cools down more...
So... more tests. Another pressure test (cold) shows it holds it's pressure easily. Another hydrocarbon test shows nothing, after 5 minutes (last time it changed at 1 minute, the standard test time).
I think I might be overfilling it so I've tried putting less water in - symptoms exactly the same.
What I did notice though (prompted largely by an email from another PHer, thanks John) was that there is hardly any radiator exposed to direct air flow. I took a pic and shaded bits for clarity:
The red bits are the oil cooler. The white bit is the number plate, obviously. The yellow bits are the only bits of the radiator you can see from head-on - the intake air scoop takes up nearly all the space above the plate.
My reckoning is: at high speeds the ram-effect pushes air through the radiator. At idle, the fans can suck enough air through to stabilise the temperature. When moving slowly though, the engine is generating slightly more heat, more than the fans can cope with, and there's no ram-effect so the radiator isn't working properly.
So next step is: clean through the radiator fins with a jet wash, then try taking the number plate off, and then if necessary, leave the fans on all the time.
I just this minute thought of something else - if the fan is wired up to turn the wrong way, it'll work ok when fast because there's enough air getting forced through. It'll work when stationary even if the fan is blowing instead of sucking. But if moving slowly, the fan is trying to blow air one way while the car is generating a gentle breeze in the other direction, so the air won't actually move through the radiator fins at all. Another thing to check!
It's driving me mental...
Edited by tvrgit on Friday 4th September 14:38
I think you're just delaying the inevitable I'm afraid.
If you had hydrocarbons in the water then you have a leak, however mild. In honesty, it's only ever going to get worse. I see where you're going with the airflow thing, but it's only the same as any other Cerbera and I just don't think that they are that marginal on the cooling, mine certainly isn't.
If you had hydrocarbons in the water then you have a leak, however mild. In honesty, it's only ever going to get worse. I see where you're going with the airflow thing, but it's only the same as any other Cerbera and I just don't think that they are that marginal on the cooling, mine certainly isn't.
Onzlouk said:
With the large mouth they have though the radiators do get grimey, which isnt good. we sprayed GUNK on mine a couple of weeks ago when we were changing the coolant pipes then jet washed it, now its as it should be and you can spy through the fins.
I can't see through the radiator at all...It's possible that there is more than one problem now. Cooling getting worse when the car is moving slowly does seem to point to fans running backwards and maybe the original problem is something quite simple like that. It's possible that the repeated hot running has caused some other problems such as HGF, in which case you need to ensure that you fix the underlying problem as well as the HGF. I would say though from the symptoms described that it's far from certain that you have HGF.
Another update:
I repeated the block test for 5 minutes this time, after pitting some block sealer in a couple of weeks ago, and there was no sign of any hydrocarbons this time. I phoned another TVR specialist (the one recommended by the first one) who said I should bleed it again, with the engine running and heater on full blast. He also said I should jet wash the radiator.
So I did. I also cut an inch off each end of the number plate, and decided not to refill it and see if it finds it's own level.
Also was in another Cerb last weekend that runs a LOT hotter then mine, and with no water visible in the expansion tank. He says he's never filled it...
Finally got a chance to try it today, 50 miles fast and slow, including 20 minutes stuck in a queue doing about 200 yards at the Royal Highland Show. Needle moved about a bit but only once ant over 90 (to about 93) but otherwise it looked perfect. No sign of coolant escaping round the expansion bottle either.
After I'd relaxed a bit, I decided to try it windows up, aircon on - and decided that the Verb is a damn fine place to be (when it's working) so we'll see how it goes!
I repeated the block test for 5 minutes this time, after pitting some block sealer in a couple of weeks ago, and there was no sign of any hydrocarbons this time. I phoned another TVR specialist (the one recommended by the first one) who said I should bleed it again, with the engine running and heater on full blast. He also said I should jet wash the radiator.
So I did. I also cut an inch off each end of the number plate, and decided not to refill it and see if it finds it's own level.
Also was in another Cerb last weekend that runs a LOT hotter then mine, and with no water visible in the expansion tank. He says he's never filled it...
Finally got a chance to try it today, 50 miles fast and slow, including 20 minutes stuck in a queue doing about 200 yards at the Royal Highland Show. Needle moved about a bit but only once ant over 90 (to about 93) but otherwise it looked perfect. No sign of coolant escaping round the expansion bottle either.
After I'd relaxed a bit, I decided to try it windows up, aircon on - and decided that the Verb is a damn fine place to be (when it's working) so we'll see how it goes!
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