Erratic Temp Readings
Discussion
Took the tiv out this morning (well was planning to), did the usual routine of take cover off, start her up and leave running whilst lock up cottage.....normally sat running max 2 mins.
Hopped in, did the usual check of the gauges - all OK so off we went. Only got 3 mins down the road and noticed the temp gauge suddenly shoot up in the red, as approaching a car park we did a swift left at which point the temp gauge went straight back down to the point you would expect for an engine that had only been running for 5 minutes. Brought the beasty back home, temp gauge sat nice and steady all the way back, switched engine off and proceeded with my duties in the other car.
When I came back an hour later, I popped up bonnet, checked water, leaks all the obvious and started the engine up again. All Ok, but again 3 mins in the temp gauge shot up in the red but dropped almost as quickly (we're talking 6/7 seconds time span here)and the fan didn't come on.
I left beasty running and the temp gauge gradually got to its normal opperating point (half way) and obviously as the engine got warmer, gradually crept up till the fan came on and the temp went back down to the normal operating range, but at no point this time did it even get close to the red, just held nice and steady as you would expect.
Any tips as to what is going on here, dodgy sender unit, wiring or gremlins
Hopped in, did the usual check of the gauges - all OK so off we went. Only got 3 mins down the road and noticed the temp gauge suddenly shoot up in the red, as approaching a car park we did a swift left at which point the temp gauge went straight back down to the point you would expect for an engine that had only been running for 5 minutes. Brought the beasty back home, temp gauge sat nice and steady all the way back, switched engine off and proceeded with my duties in the other car.
When I came back an hour later, I popped up bonnet, checked water, leaks all the obvious and started the engine up again. All Ok, but again 3 mins in the temp gauge shot up in the red but dropped almost as quickly (we're talking 6/7 seconds time span here)and the fan didn't come on.
I left beasty running and the temp gauge gradually got to its normal opperating point (half way) and obviously as the engine got warmer, gradually crept up till the fan came on and the temp went back down to the normal operating range, but at no point this time did it even get close to the red, just held nice and steady as you would expect.
Any tips as to what is going on here, dodgy sender unit, wiring or gremlins
Edited by coolcatmaz on Wednesday 3rd October 16:17
coolcatmaz said:
Any tips as to what is going on here, dodgy sender unit, wiring or gremlins
The sensor is a thermister, and a high reading on the gauge corresponds to a low resistance from the sender. That could be caused by a wiring short, or a failure within the sender itself.
Check the coolant level too, because low coolant level leading to an air lock can cause sudden temperature swings (but not usually as fast as the ones you're describing).
A quick and easy safety test if this happens again is to put the heater on hot. As long as hot air comes out you know you have coolant circulating. If the heater stops working this suggests that your cooling system isn't working, you need to pull over and switch off straight away.
coolcatmaz said:
Any tips as to what is going on here, dodgy sender unit, wiring or gremlins
dodgy sender unit: maybewiring: probably
gremlins: Nah, TVR's come with gremlins as standard equipment, so nothing to worry about.
If the needle takes a few seconds to move to the 'hot' position it could be an air bubble as described: check level in swirl pot, check if heater functions and bleed air from the radiator, using the bleed nipple. If an air bubble causes the poblem, watch out, as overheating can cause engine damage.
If the needle shoots up past 'hot' very suddenly, and then jumps down to normal very suddenly again, i expect it to be the wire going to the sender. probably the wire is chafing against the engine or another metal part, exposing the copper wire and causing a short circuit. Check the wiring around the engine block for chafing marks or bare copper wire.
Right then boys, I've got my stickly little hands all greasy and had a fiddle.
Now, I've not driven it anywhere today but just let it tick over on the drive. I have again checked the coolant levels and theres adequate in the expansion tank, I started her up, put the heater on full blast, got comfy and watched the needle.
For what seemed like an eternity (I do get impatient) it finally started to budge, then rouse rather swiftly again up to the red mark (but not in the red) and dropped back down to a cooler temp before creping up and holding steady at just under/around the 90 mark (its normal running temp)before rising and the fan cutting in, and thus dropping accordingly.
The upside is that tonnes of hot air was blasted out through the heater so we know coolant is circulating.
Are we thinking loose wires.....cant see any with copper/chaffing though, not that I'm a mechanic mind you
Now, I've not driven it anywhere today but just let it tick over on the drive. I have again checked the coolant levels and theres adequate in the expansion tank, I started her up, put the heater on full blast, got comfy and watched the needle.
For what seemed like an eternity (I do get impatient) it finally started to budge, then rouse rather swiftly again up to the red mark (but not in the red) and dropped back down to a cooler temp before creping up and holding steady at just under/around the 90 mark (its normal running temp)before rising and the fan cutting in, and thus dropping accordingly.
The upside is that tonnes of hot air was blasted out through the heater so we know coolant is circulating.
Are we thinking loose wires.....cant see any with copper/chaffing though, not that I'm a mechanic mind you
When the car is cold is the swirlpot tank full? The expansion tank only works properly when the swirlpot is full AND the pressure cap on the swirlpot is working properly. From what you've described I'd be looking for air locks first and possibly a suspect pressure cap. If you've not replaced the cap then for the sake of 3 quid I'd suggest fitting one - QH FC53 is the part number. It will need a rubber sealing washer made up from something like a mountain bike inner tube because they don't come with them.
There is one thing that I didn't like about the pipes on my S3 and that is the pipe that goes from the thermostat housing, over the 1200mm alternator belt
to the swirlpot. Because it goes above the height of the swirlpot it is a place where air can sit in the system and isn't something I liked. Therefore I used a straight bit of pipe from the thermostat housing to the swirlpot that goes through the middle of the belt. Means that I have to break the cooling system to change the belt but I can live with that.
Haven't got any pics at the moment but will sort one out later.
There is one thing that I didn't like about the pipes on my S3 and that is the pipe that goes from the thermostat housing, over the 1200mm alternator belt
to the swirlpot. Because it goes above the height of the swirlpot it is a place where air can sit in the system and isn't something I liked. Therefore I used a straight bit of pipe from the thermostat housing to the swirlpot that goes through the middle of the belt. Means that I have to break the cooling system to change the belt but I can live with that. Haven't got any pics at the moment but will sort one out later.
Jed-S said:
When the car is cold is the swirlpot tank full? The expansion tank only works properly when the swirlpot is full AND the pressure cap on the swirlpot is working properly. From what you've described I'd be looking for air locks first and possibly a suspect pressure cap. If you've not replaced the cap then for the sake of 3 quid I'd suggest fitting one - QH FC53 is the part number. It will need a rubber sealing washer made up from something like a mountain bike inner tube because they don't come with them.
There is one thing that I didn't like about the pipes on my S3 and that is the pipe that goes from the thermostat housing, over the 1200mm alternator belt to the swirlpot. Because it goes above the height of the swirlpot it is a place where air can sit in the system and isn't something I liked. Therefore I used a straight bit of pipe from the thermostat housing to the swirlpot that goes through the middle of the belt. Means that I have to break the cooling system to change the belt but I can live with that.
Haven't got any pics at the moment but will sort one out later.
Wheres the damn swirl pot then? and I will check it There is one thing that I didn't like about the pipes on my S3 and that is the pipe that goes from the thermostat housing, over the 1200mm alternator belt
to the swirlpot. Because it goes above the height of the swirlpot it is a place where air can sit in the system and isn't something I liked. Therefore I used a straight bit of pipe from the thermostat housing to the swirlpot that goes through the middle of the belt. Means that I have to break the cooling system to change the belt but I can live with that. Haven't got any pics at the moment but will sort one out later.
What you describe sounds like a normal functioning cooling system: engine slowly gets warm, temperature rises slightly over 90', then fan kicks in (so otter switch, relay, wiring and fan are working) and brings temp back to slightly under 90'. Heater works, so no air bubbles there either. At least this doesn't look like a serious problem with the cooling. I stick with my 'dodgy wiring' diagnosis, but that may be difficult to find. Just ask the garage to look at it when you bring it away for the brakes.
http://olavbergman.nl/images/stories/PICT1054a.jpg
Swirlpot is the black vertical tube with metal cap on the left, where all the blue wires are running to. Take the cap off when the engine is cold, otherwise the coolant could scald your stickly little hands. Swirlpot should be full, overflow tank (RH bulkhead) should be 1/3-half full.
BTW: welcome to the greasy hands club!
http://olavbergman.nl/images/stories/PICT1054a.jpg
Swirlpot is the black vertical tube with metal cap on the left, where all the blue wires are running to. Take the cap off when the engine is cold, otherwise the coolant could scald your stickly little hands
. Swirlpot should be full, overflow tank (RH bulkhead) should be 1/3-half full.BTW: welcome to the greasy hands club!
Cheers Ron, I know exactly where the swirl pot is now, only mine is a red one and I was wondering what exactly it was before you pointed it out I'll have a look at it tomorrow if it stops raining.
I know the overflow tank is ok on coolant level as I've checked there. Not sure things are running quite as normal as you think, the temp gauge is very erratic and is leaping up and down like a kangaroo on steriods
but it does hold steady when its not doing that.
Its booked in next week to have the water pump and a full hose replacement done (I've only had the stuff sat at home in a box for over 2 months) and I'm getting the fan belt changed as well as noticed today it's pretty slack and worn and at the end of its adjustment.
Thankyou for your help and a piccy....much, much appreciated
I'll have a look at it tomorrow if it stops raining.I know the overflow tank is ok on coolant level as I've checked there. Not sure things are running quite as normal as you think, the temp gauge is very erratic and is leaping up and down like a kangaroo on steriods
but it does hold steady when its not doing that.Its booked in next week to have the water pump and a full hose replacement done (I've only had the stuff sat at home in a box for over 2 months) and I'm getting the fan belt changed as well as noticed today it's pretty slack and worn and at the end of its adjustment.
Thankyou for your help and a piccy....much, much appreciated
You say it eventually settles down - that points to air somewhere so now you know where the swirlpot is do check the level. As mentioned, wait until the engine is cold before removing the cap.
Also a loose alternator belt has the potential to cause cooling issues if it is very loose. Check the water level and top up then get it to the garage who should give thta side a good once over while they're doing the other bits.
Also a loose alternator belt has the potential to cause cooling issues if it is very loose. Check the water level and top up then get it to the garage who should give thta side a good once over while they're doing the other bits.
Jed-S said:
You say it eventually settles down - that points to air somewhere so now you know where the swirlpot is do check the level. As mentioned, wait until the engine is cold before removing the cap.
Also a loose alternator belt has the potential to cause cooling issues if it is very loose. Check the water level and top up then get it to the garage who should give thta side a good once over while they're doing the other bits.
Dont get me wrong when I say it settles. The needle rockets up to red and straight back down in a matter of seconds (even from stone cold), and then will either hold at 90 if the engine is up to temp, or will gradually rise to 90 if its obviously cold and then sit quite happily. Also a loose alternator belt has the potential to cause cooling issues if it is very loose. Check the water level and top up then get it to the garage who should give thta side a good once over while they're doing the other bits.
I sat in it for quite some time today watching and the needle did this several times over a period of about 15 mins. Once its at 90, anything above and the fan kicks in, just concernes me that the gauge keeps leaping about in between.
I will do my checks tomorrow, car is grounded anyway now till next week as i dont like the look of the fan belt nor whats going on with the temp gauge.
If the gauge is jumping erratically you can guarantee that its an electrical fault.
The temperature sensor is very voltage sensitive - 100mV will make a big difference.
If you have the common problem of ignition switch connector bad contacts then you will get this effect.
The connection to the temperature sensor is also likely to be corroded and will need cleaning.
Mine did exactly the same and it wasnt too difficult to have a gentle prod around behind the dash and locate where the dodgy connection was.
Mine was the earth wire.
The temperature sensor is very voltage sensitive - 100mV will make a big difference.
If you have the common problem of ignition switch connector bad contacts then you will get this effect.
The connection to the temperature sensor is also likely to be corroded and will need cleaning.
Mine did exactly the same and it wasnt too difficult to have a gentle prod around behind the dash and locate where the dodgy connection was.
Mine was the earth wire.
OK then, latest update.
I have checked the swirl pot, now when you say 'full' I assume you mean 'full'. Well it wasn't full (probably 2/3 full) but it's full now.
I've run the car (only on the drive) and bled the radiator but no air came out, assumed my normal position behind the controls, coffee in hand and watched the gauge.
NO ERRATIC READINGS
just gently crept to its normal operating position and stayed there for a good 10 mins before rising slightly until the fan came on and then dropped back down to 90 (and yes loads of hot air coming through)
Its still grounded till its been to the garage next week, and I'll get a new pressure cap to be on the safe side when I pop and get a fan belt, and I'm sure the guys at the garage will give it a good check when the water pump gets changed.
Do believe you guys may make a mechanic of me yet
I have checked the swirl pot, now when you say 'full' I assume you mean 'full'. Well it wasn't full (probably 2/3 full) but it's full now.
I've run the car (only on the drive) and bled the radiator but no air came out, assumed my normal position behind the controls, coffee in hand and watched the gauge.
NO ERRATIC READINGS
just gently crept to its normal operating position and stayed there for a good 10 mins before rising slightly until the fan came on and then dropped back down to 90 (and yes loads of hot air coming through)Its still grounded till its been to the garage next week, and I'll get a new pressure cap to be on the safe side when I pop and get a fan belt, and I'm sure the guys at the garage will give it a good check when the water pump gets changed.
Do believe you guys may make a mechanic of me yet
Righty then, its back from the garage and its had new hoses all round, new water pump, new fan belt and the system has been flushed and fresh coolant added.
The query is this -
I took it for a short run today as didn't really have time yesterday when I picked it up from the garage (said garage is just up the road). Anyway, it sounds good and is frisky as a cat on hot tiles, BUT the temp gauge is taking ages to move, even after 20 miles it was still only sitting on roughly 70, and didn't rise above till I left it sitting on the drive, when eventually the fan came on as normal between 90 & 100.
Am I correct in saying it's normal operating temp is 90? Is it because maybe things are working correctly now that its taking longer to warm up or is something else wrong? I checked the swirl pot before I went anywhere whilst the engine was cold and I had to put perhaps a pint of water in. I will check it again tomorrow when the engine is cold. Whats going on here if I need to put more water in? Its not leaking and the oil looks good.
Probably nowt to worry about, but I want to do the Rutland Rumble on Sunday and the last thing I want to do is break down or mess the engine up.
The query is this -
I took it for a short run today as didn't really have time yesterday when I picked it up from the garage (said garage is just up the road). Anyway, it sounds good and is frisky as a cat on hot tiles, BUT the temp gauge is taking ages to move, even after 20 miles it was still only sitting on roughly 70, and didn't rise above till I left it sitting on the drive, when eventually the fan came on as normal between 90 & 100.
Am I correct in saying it's normal operating temp is 90? Is it because maybe things are working correctly now that its taking longer to warm up or is something else wrong? I checked the swirl pot before I went anywhere whilst the engine was cold and I had to put perhaps a pint of water in. I will check it again tomorrow when the engine is cold. Whats going on here if I need to put more water in? Its not leaking and the oil looks good.
Probably nowt to worry about, but I want to do the Rutland Rumble on Sunday and the last thing I want to do is break down or mess the engine up.
[quote=coolcatmaz]
I had to put perhaps a pint of water in. I will check it again tomorrow when the engine is cold. Whats going on here if I need to put more water in? Its not leaking and the oil looks good.
quote]
If your water level is dropping but you dont see any leak, you should check your expansion tank. The hot water should expand into it and then be drawn back into the swirl pot when the engine cools. So maybe the water is either not making it to the expansion tank or is exiting the expansion tank via the overflow pipe or is not being drawn back into the swirl pot...
when the engine is warm, check the overflow pipe from the expansion tank to see if any water or steam is coming out. If not note the level the water in the tank and compare it when the engine cools down again - it should then be lower.
K
I had to put perhaps a pint of water in. I will check it again tomorrow when the engine is cold. Whats going on here if I need to put more water in? Its not leaking and the oil looks good.
quote]
If your water level is dropping but you dont see any leak, you should check your expansion tank. The hot water should expand into it and then be drawn back into the swirl pot when the engine cools. So maybe the water is either not making it to the expansion tank or is exiting the expansion tank via the overflow pipe or is not being drawn back into the swirl pot...
when the engine is warm, check the overflow pipe from the expansion tank to see if any water or steam is coming out. If not note the level the water in the tank and compare it when the engine cools down again - it should then be lower.
K
Bear in mind that the level in the expansion tank may not coincide with the level markings for Ford. Some happily run with the expansion tank nearly empty and if filled, this will just overflow out again. Better to check the level (cold) in the swirl tank.
The engine does take a while to warm up, especially in cold weather. 90 should be max temperature.
The engine does take a while to warm up, especially in cold weather. 90 should be max temperature.
yes I was a good girl and replaced the pressure cap as directed. The water level seems to be traveling back and forth between swirl pot and expansion tank as normal.
I've checked the water level again in the swirl pot and it has dropped back to the level it keeps dropping to, but no further. Maybe the car likes running at this level.
I'm off out to give it a good run (armed with a bottle of water) and we'll see how it goes.
I've checked the water level again in the swirl pot and it has dropped back to the level it keeps dropping to, but no further. Maybe the car likes running at this level.
I'm off out to give it a good run (armed with a bottle of water) and we'll see how it goes.
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