Evening folks, I've got a '96 2.0 8v megane that has recently started running hot. out of 6 bars it always used to run at the 1st bar, rising to the second if stuck in traffic before returning to the first bar once progress is resumed. earlier in the week I noticed it was running at the third bar. after checking the fluid levels which are fine I removed the thermostat and after testing it's stuck closed. now even with the thermostat removed the car is still running hot and the fan doesn't appear to kick in. I've replaced the fan switch with a new one and also checked the fan works.
now the temperature is getting up to the fourth bar, when i first fitted the new fan switch the fan kicked in at about 4.5 bars fine, now it doesn't appear to kick in at all, ive bled the coolant system but can only find two bleed nipples, one on the thermostat housing and the other behind it on the heater hose, should there be one for the radiator? both the top and bottom radiator hose are equally hot (not red hot though i can comfortably touch them) so I presume the radiator isn't blocked, you also get a good flow of water round the system if it is filled via the top rad hose with a hosepipe.
i believe the water pump is working as there is a pipe from the top of the thermostat which goes up vertically and then 90 degrees and enters the coolant tank above the max line and when the engine is gently revved you can see the coolant pouring into the tank, are there any other ways I can test the water pump?
if the fan switch is bypassed to run all the time then the car heats up to just over 4 bars and stays there constantly, oddly if you turn the heater on the temperature gauge goes up slightly and the air isn't that warm, id expect the temperature to go down as your directing hot air away from the engine.
now im not sure what is wrong, I don't think it's head gasket failure as there are no other signs except the running hot, although i plan to do a compression test tomorrow which may give a bit more of an idea, if not then a sniffer test will have to be done. i also need to test the new fan switch with a multimeter to check it works.
would appreciate any other ideas on this though?
chris
Edited by Pugugly on 05/10/2008 at 22:12
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Hi Chris, If the heater is not getting hot then i would suspect the water pump or headgasget. Take off the oil filler cap and check for white deposits. Also have a look at the dipstick for the same. Do you get any warning lights. With the engine warm carefully take off the header tank cap to check for exess pressure, it should just give a whoosh a bit like opening a bottle of lemonade and then calm down.Also have a look at the water coming through with the engine running to see if is bubbling or foamy.This is a sign of headgasget failure. Put a new thermostat in as without one the heater will be cold. If the car has boiled up this could have damaged the headgasget or head itself.You are right to do a compression test.
Thats about all i can think of. Derek
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Start with the simple things, why do you believe the temperature gauge and sensor are reading correctly?
Does it actually exhibit any signs of overheating?
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well, new thermostat in (it works checked before fitting), still shows hot on the gauge, but the heating is warm again. compression test done, figures are all fairly close so im even less inclined to think it's hgf as it doesn't display any other symptoms.
there are no actual signs of it overheating except the gauge no, all coolant hoses are equally warm and there are no signs of excessive pressure. ive bleed the system and im certain there's no airlocks. i have discovered though that the needle on the gauge goes up slightly whenever you turn the heater fan on, regardless of the heater setting, im now leaning towards the actual gauge sender being faulty, is there anyway of testing it? does anyone know which sensor it is as there are a couple it could be in the engine bay although i suppose i can test by unplugging them till the gauge drops to zero.
apart from a faulty sender im now out of ideas as to a cause.
cheers
chris
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I would change the coolant temp sensor anyway. Try cleaning the earth strap which is located on the left hand side of the bulkhead at the rear of the engine compartment near to the battery.
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I would agree. All the indications are that it is not running hot at all, just that the gauge is telling you porkies.
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