thermostat hose

[markbrum]

seat leon cupra r 210 amk, ok quick question for you very talented lot, why does the hose that leads from my thermostat never get hot??, yet i have excellent hot air through vents, car never goes over 90 on temp gauge, and generally running ok... i've never really understood the cooling system on this car, so any real ideas if its a problem or am i just being daft , any help if i need it realy welcome....thankyou

 

[Muttley]

Because it's on the cold side of the radiator, the return to the water pump.

The thermostat itself is sitting in the water jacket around the engine, so opens according to engine-coolant temperature. It's purely mechanical, a cylinder of wax that expands significantly when it melts to open the valve. On the other side is the return hose from the bottom of the radiator. It shouldn't be stone cold, but only warm even on a hot day after a run.

 

[markbrum]

so in your opinion maybe a lazy thermostat?

 

[Muttley]

When are you testing the temperature? Idling on the driveway or after a run long enough to get the dash gauge up to 90?

 

[markbrum]

both...the bottom pipe never seems to get even warm

 

[Muttley]

If the thermostat was stuck, or if there was any other problem with coolant circulation, then you'd see the engine overheating. The cabin heater acts as a small radiator, but unless you're running with the heater up full it shouldn't be able to make that much difference.

Does the top hose get hot? If so, that confirms that coolant is circulating through the radiator.

I've found a diagram of the AMK coolant hoses.

 

[markbrum]

sorry for late reply, yes top hose is always hot, also with heaters not on the car never over heats at all, spoke to my mate who does a lot of work on vw's and he said its fine he reckons the amk engine is the better of the 2 engines on the cupra r's said he never seen an amk engine over heat unless its water pump related or blocked rad he said same as you, he checked return flow to expansion tank steady and increases with engine speed thats most of the proof needed everything is fine, he was concerned my fans work with aircon but never seem to kick in when hot, he tested fans both fine ( the bridging trick on connector ) slow works fine and also fast speed, so he tested rad sensor thats fine, so he thinks its the fan module under battery, he said he seen these breakdown so hes going to borrow one of a golf mk4 and try it with mine, he knows it works because he just done waterpump and thermostate on the golf and knows the fans kick in when they shud, he does all my maintenance on car and said your oil changes are always normal you can tell by the oil if theres been any over heating...so ill keep you posted on what if anything he finds, his famous last words was maybe you just have a very efficient cooling system, he did also point out i could do with a new expansion cap mine seems to be missing a seal, which he said doesnt help lol..