Car engine overheating

Associate
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10 Jan 2022
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Northern Ireland
I bought a 2010 seat Leon that got a new head gasket, timing belt and water pump installed before I collected the car.

I have recently noticed the car has started to slightly overheat again (not to boiling point nor is there any warning lights coming up) and goes back down to 90 (stays there for a while and then goes back up to 100-110 degrees). This only happens when I’m on the motorway doing 70 or 80 mph and it doesn’t happen when driving through a town at lower speed. I have also noticed that the fan is working more than it should be even when the engine is off. There is enough oil and coolant levels within the car.

There is a hissing (similar to switching on nitro) sound when I take my foot of the accelerator and vibration (when speeding up) at the front end of the car. I don’t know if that could be a problem in relation the temperature issue. The heater motor seems to be ok because there is respectable heat coming through and I switch this on when I first see the temperature raising.

Any help would be much appreciated.

Thanks
 
Soldato
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First thing to check that is normally easy to check is that the fins on the Rad are clean and not clogged up with dirt or something else
 
Associate
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Probably needs some professional diagnostics as it could be an air lock or the pressure cap needs replacing or the system needs a pressure test. Hard to diagnose remotely.
 
Soldato
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Have you checked oil in the water or water in the oil?
It will go to like mayonnaise so if you remove the filler caps it should be on there, I'd bet the head hasn't been skimmed wen the head gasket was done and if not could've warped.
It really does need looking at by a independent garage as where you got it from will probably just say it's normal as it's temperature goes back down, how long have you had the car?
 
Soldato
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Could be lots of things, you could be lucky and it could just need a good bleed as there's air in the system or a dodgy thermostat. Or it could be a crack in the block or a warped block or head or any number of other things.

What is the cars history and why did it require a head gasket?
 
Man of Honour
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It could be many things. If the car was bought from a dealer recently then I would report it immediately and ask them to look at it. The head gasket on a 2010 car is a bit of a warning that something went quite wrong so I would have been asking a bit more about the history of the car.
 
Soldato
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Probably cracked engine.

Or air trapped in the cooling system.

Never buy a car that's overheated.

A cracked 'engine' (it'd be head or block, not both) wouldn't give intermittent issues - you'd know about the problem even when pottering.
An air lock would also cause issues at lower speeds due to less airflow through the radiator, and as for never buying a car that's overheated - how would you know?
My current car has a receipt for a thermostat in the history at 60k, this may or may not have been overheated but there's no way I'd ever be able to find out. I do know it can't have done much harm, as we're ticking along nicely at 221k now :)
 
Soldato
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Probably cracked engine.

Or air trapped in the cooling system.

Never buy a car that's overheated.

Best advice, if slightly late to help the OP.

As with all closely toleranced, heat-treated mechanical devices, operating above its designed temperature for any length of time causes significant premature wear/damage.
 
Caporegime
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block 16, cell 12
A cracked 'engine' (it'd be head or block, not both) wouldn't give intermittent issues - you'd know about the problem even when pottering.
An air lock would also cause issues at lower speeds due to less airflow through the radiator, and as for never buying a car that's overheated - how would you know?
My current car has a receipt for a thermostat in the history at 60k, this may or may not have been overheated but there's no way I'd ever be able to find out. I do know it can't have done much harm, as we're ticking along nicely at 221k now :)

He knew. That's why he told us.

I put a new thermostat in my 3000gt just because. But op sounds like he was aware.
 
Soldato
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3 May 2012
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4,864
It's not uncommon for the temperature to do that on some vehicles.

Radiators and cooling systems are designed to handle most climates, as it cold in the UK right now, it might be cooling too well.

There will be a solenoid that shuts off the water pump until the temp goes back up.

If the OP says on a motorway could be this, freezing damp air rushing over the radiator, and why not a much at low speeds.

It could also be ****** :)
 
Soldato
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Shropshire
Get a different garage to do a combustion gasses in the coolant test. They can use either a dedicated tool that draws air / gasses from above the coolant in the header tank, or carefully use the MOT emissions tester, if they are an MOT station (or have an emission testing machine).

You can probably buy your own bubble through a liquid tester on eBay for not too much money these days, they are usually a clear plastic tube with a squeeze bulb on top to pull gasses through the liquid. If the liquid changes colour there are combustion gasses present, and there shouldn't be!

Free tip, if you buy the tester the liquid is quite dear, but if you bubble clean fresh air through it for a couple of minutes after it has changed colour on a positive test, it will revert to its original state and can be used again a few times.

I tend to use my 4 gas analyser though, but if you let it suck coolant in you can do it a nasty mischief...
 
Associate
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could be thermostat, my wifes car would make an intermittent bong noise but no fault was logged, plugged in my OBD2 reader and watched the data in real time when driving and could see the temp was going higher than it should at times whilst making progress along the road.

Took to garage who replaced the thermostat and it was fine after that.
 
Associate
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Location
Portsmouth
It's not uncommon for the temperature to do that on some vehicles.

Radiators and cooling systems are designed to handle most climates, as it cold in the UK right now, it might be cooling too well.

There will be a solenoid that shuts off the water pump until the temp goes back up.

If the OP says on a motorway could be this, freezing damp air rushing over the radiator, and why not a much at low speeds.

It could also be ****** :)
As far as I know the 1P leons do not do this. Overheating under load is sadly indicative of a head gasket issue (pressurised combustion gas displaces water in the cooling channels resulting in increased temperatures) :/
 
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