erratic overheating

[pardizzle21]

hello all,
iv recently been experiencing problems with overheating.I had the problem before but fixed it, as the coolant needed bleeding(had an air lock)
It happened today on a motorway,after about 40 miles it started slowly getting hotter and hotter, when i slowed down it seemed to get worse, but was fine at higher speeds.
Its got oil, coolant and there are no leaks and its not an air lock, anyone think the car would overheat if the fan was cuming on too late/not at all?
any experience on heating issues appreciated! thanks

[saxophonias]

maybe you burnt the head gasket? Check the coolant box for mixes with oil. Check out to see how it works when it is cold

[Firebass]

check the sensor of the thermostat or the thermostat itself (i dont know if this is the correct term ) i changed my water pipes to silicone ones and we forgot to put back the sensor and i had overheat also without leakings but it was that )

[saxophonias]

Broken thermostats tend to stay open so as not to create overheat. So if it is broken you should experience very low temperatures. Still you never know so have it checked

[pardizzle21]

thanks for the replies, i should of mentioned the thermostat was replaced at the time i had an air lock (a few months back) so it should be fine...
The head gasket is only 3 months old and was fitted by my friend(qualified mechanic)-But i did notice alot of crap/brown had got into the coolant expansion tank making me think the worst...but iv cleaned it out and none has come back....???? blagged:?
A friend mentioned a fan relay, is it worth replacing it?/temp sensor?

cheers

[saxophonias]

Firstly you need to see whether the fan is working while the temp is more than it should. Don't use your engine in high temperatures as it is the easiest thing to burn the gasket or even damage the valvetrain. It is important to tell us whether the engine works properly on cold starts. Also when you hit the gas pedal do you hear any weird sounds like water sounds bubbles etc?

[pardizzle21]

hi, yesterday i had alot of points checked..

*tested fan switch-came on fine
*tested switch into thermostat housing-fan came on fine
*checked fan relay and fuses-working fine

Bubbles???hmmm yes sometimes i do think i here them on start up....could be in my head tho....

Im going to replace thermostat,then try the thermostat switch(even tho it seems to work)

This overheating is really annoying, becus it isnt all the time. i pulled over twice yesterday while overheating and the fan wasnt on, BUT if i leave the car running on standstill the fans do kick in.... gggrrrrrrr

thanks

[pardizzle21]

* sax- what do u mean by properly in the cold? the car starts up fine and seems to come to temperature quite normally-its after youv done a few miles it seems to play up
thanks

[hondamake]

Hi Tom. Hate to be the prophet of doom but it sounds to me very like pressurisation of the water jacket. Air enters the cooling system creating air pockets which prevents water circulation. Very difficult to diagnose because once the engine cools down everything goes back to normal, no water loss and the problem may not re-occur for days. The air must be coming from a cylinder(s), because greater pressure than the cooling system's is required. First and most obvious cause is the head gasket but you also have to consider block/cylinder cracks/porosity plus liner issues. The correct diagnostic route to follow, before you slit your wrists, is:- 1. Take the thermostat out and bin it, if it solves the problem QED. 2. Check the radiator core for cool patches, progressive deterioration and silting will cause blocked galleries resulting in insufficient heat transfer. 3. Go to your local MOT man and bribe him with some beer tokens to use his exhaust gas analyser to "sniff" your header tank, if hydrocarbons are present in large amounts then go back to the top of the page.

[pardizzle21]

hi steve, lol 'the prophet of doom' Im running out of ideas on what could be the cause of the issue. its a weird one, mainly because the car only overheats after its been thrashed OR you get the car to a really warm temperature through long distance.
So far
-thermostat inspected-fine
-sensor into thermostat housing-replaced OEM
-radiator flushed-fine
-fan relay tested-fine
-fan switch-tested-fan comes on
-Just had the coolant system bled, drove 10-15 miles and the heat crept up again.it SEEMS that when i take my foot off the gas pedal and engine brake, the temp quickly comes down, unless i have been motorway driving

I think the head gasket is good, as there is no oil in the expansion tank.the rad flows fine, no leaks in the system and there should be no air lock, so im really scratching my head!
could it be signs of the water pump breaking down, as its done 111.000 miles?
Times like this i regret being solely dependent on one car!!

all help appreciated