Low temp on the move, strange but do you know why?
Discussion
My water temp guage works fine at low speeds and at idle but as the revs get higher the temp drops on the readout until it is right at the bottom. If I slow to a stop it shoots up to show the actual temperature.
I have a small leak on the water pump but that's all and is minimal, could this be the cause?
I have a small leak on the water pump but that's all and is minimal, could this be the cause?
GreenV8S said:
Sounds like an electrical issue, maybe damaged wiring being disturbed as the engine moves, or a poor power/earth causing a voltage dip somewhere as the electrical load varies.
Hi Peter,
I thought that too, so I gave all the connectors a wiggle when I got back but of course I was standing still and the reading was normal.
I'll get my water pump replaced and see what it is like after, could be air going around the sensor perhaps??
Does it vary with revs even when you are out of gear (when stationary, for example)? It would be quite extraordinary for the engine temperature to vary enough to be visible, within a few seconds. Basically it just isn't going to happen, the engine has far too much thermal inertia. If the engine runs out of water so the sensor is dry instead of immersed in water it would cause eratic readings, but I assume you have already checked the level and bled engine and radiator.
It will climb to a normal reading as I slow from 60mph, anything above 40mph and it's at the bottom of the gauge.
The engine was hot but not too hot after a run, well the fan didn't cut in until I stood at idle speed for a couple of minutes, which is normal on my car.
Standing at idle speed, I wiggled the connector and it didn't budge from a normal reading.
I did take the swirl pot cap off the other day (whilst hot) and a fair bit of water shot out but I topped up and all seemed fine. Perhaps there is an airlock at a certain engine speed?
Where are the bleed points on the S2, do I bleed with engine running or does this suck more air in??
The engine was hot but not too hot after a run, well the fan didn't cut in until I stood at idle speed for a couple of minutes, which is normal on my car.
Standing at idle speed, I wiggled the connector and it didn't budge from a normal reading.
I did take the swirl pot cap off the other day (whilst hot) and a fair bit of water shot out but I topped up and all seemed fine. Perhaps there is an airlock at a certain engine speed?
Where are the bleed points on the S2, do I bleed with engine running or does this suck more air in??
So it varies with vehicle speed not engine speed? Symptoms kind of similar to running with no stat, but more severe.
Can you confirm the stat is actually fitted and working? One easy way is to start the engine from cold and feel how long it takes for the bottom of the radiator to get warm to the touch. Normally the radiator should stay cold until the stat opens at about 84-88 deg (depending on which stat you have), and then warm up quite quickly as the stat starts to open. If it warms up gradually over a few minutes, this suggests the stat is missing or faulty.
Can you confirm the stat is actually fitted and working? One easy way is to start the engine from cold and feel how long it takes for the bottom of the radiator to get warm to the touch. Normally the radiator should stay cold until the stat opens at about 84-88 deg (depending on which stat you have), and then warm up quite quickly as the stat starts to open. If it warms up gradually over a few minutes, this suggests the stat is missing or faulty.
GreenV8S said:
So it varies with vehicle speed not engine speed? Symptoms kind of similar to running with no stat, but more severe.
Can you confirm the stat is actually fitted and working? One easy way is to start the engine from cold and feel how long it takes for the bottom of the radiator to get warm to the touch. Normally the radiator should stay cold until the stat opens at about 84-88 deg (depending on which stat you have), and then warm up quite quickly as the stat starts to open. If it warms up gradually over a few minutes, this suggests the stat is missing or faulty.
Uhhm, not really sure vehicle speed has anything to do with it, just the associated revs with a higher road speed (i.e. more revs).
I have only been out the once and noticed this during the road test prior to fitting the new valve, I'm certain this isn't related in any way to the erratic temp reading as one is fuel and the one water. I wonder whether me taking the cap off and the lost water whilst the engine was still hot caused an air lock or perhaps the leaking water pump is sucking air in when the engine is running and causing an air lock?
I'll go for a run out tonight and see what it's like. It could as you suggest just be the stat has decided to play up and I'm jumping to conclusion about the coincidental timings?
GreenV8S said:
KentishS2 said:
Uhhm, not really sure vehicle speed has anything to do with it
I suggest you need to find out. It's easy enough to do, and is quite an important bit of evidence.
Sorry Peter, I'm not following you on this.
What is the relevance of the road speed when this happens?
I'm with you as far as the air passing through the rad at a higher speed will provide extra cooling than when moving more slowly. Perhaps it's normal and I just haven't noticed before but I'm sure I would have spotted that the temp was so low as it was right at the bottom of the gauge.
I'll go for a spin again tonight and see what happens, in true TVR tradition it will probably either be OK and won't do it again or it will self destruct!
>> Edited by KentishS2 on Monday 4th October 14:50
GreenV8S said:
Sorry Peter, I'm not following you on this.
What is the relevance of the road speed when this happens?
It tells you whether the problem changes with air speed through the radiator (implying a stat related problem) or engine rpm (implying something else).
The car behaved OK and the fan cut in and out as I would expect at the usual length of time when idling. I guess it can't be much of a problem and is probably something to do with me taking the cap off the swirl pot whilst it was hot.
I should get to the bottom of it with a little more time to check this evening ....hopefully.
Taking off the cap while the engine is hot is very silly because, apart from possibly burning you, it also causes the superheated cooling system to instantly boil as soon as you remove the pressure cap.
The water in the radiator expands and shoots out.
The water in the engine / water pump etc can't shoot out - but it tries - through any weak gasket, seal etc it can find...
your water pump leak is probably not unrelated.
neither is this, probably.
The water in the radiator expands and shoots out.
The water in the engine / water pump etc can't shoot out - but it tries - through any weak gasket, seal etc it can find...
your water pump leak is probably not unrelated.
neither is this, probably.
tvrgit said:
Taking off the cap while the engine is hot is very silly because, apart from possibly burning you, it also causes the superheated cooling system to instantly boil as soon as you remove the pressure cap.
The water in the radiator expands and shoots out.
The water in the engine / water pump etc can't shoot out - but it tries - through any weak gasket, seal etc it can find...
your water pump leak is probably not unrelated.
neither is this, probably.
It was still hot but had been standing for approx 20 mins so it would not have been boiling, just still pretty hot.
The water pump leak has been like it for a few months but is now worse but no more so since I removed the pressure cap. The bearing and seal are worn as it sometimes whines and leaks from there. I have ordered a new one now.
The gauge rising and falling is far to quick to be the sensor reacting to a change in temperature, as soon as I lift off the throttle to drop the revs the gauge returns to normal. All others gauges read perfectly OK and are unaffected so I don't think it is an earthing problem in general. I'm at a loss to know what else it could be but I'm happy that the cooling system is OK and there is no overheating. The fan takes the same amount of time as it always has to cut in and out again.
In that case it does sound electrical - my speedo used to waver about all over the place till I replaced the ignition switch connector for another reason. Can't see how they were connected, but they were!
I now have a rev counter that misreads sometimes, but returns to normal when I switch the lights on. Or sometimes not, sometimes it returns to normal when the cooling fan cuts in. But sometimes not.
Not the kind of fault that is easy to find. Yours sounds the same.
I now have a rev counter that misreads sometimes, but returns to normal when I switch the lights on. Or sometimes not, sometimes it returns to normal when the cooling fan cuts in. But sometimes not.
Not the kind of fault that is easy to find. Yours sounds the same.
tvrgit said:
In that case it does sound electrical - my speedo used to waver about all over the place till I replaced the ignition switch connector for another reason. Can't see how they were connected, but they were!
I now have a rev counter that misreads sometimes, but returns to normal when I switch the lights on. Or sometimes not, sometimes it returns to normal when the cooling fan cuts in. But sometimes not.
Not the kind of fault that is easy to find. Yours sounds the same.
I also had a speedo that used to flick but that was a poor connection and has been sorted but it still plays up sometimes when I have the heater blower and lights switched on. I will check over all the earths on the car at some point, I may even find it cures the problem. For now, at least I can stop or dip the clutch pedal (or even drive slowly, heaven forbid) to check the engine temp.
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