VW Polo - engine won't warm up

[yeager2004]

Morning.

The engine in my missus’ aged VW petrol Polo never seems to warm up – unless stationery the temperature gauge barely moves.

Some months ago, the car was in the garage having the cambelt and water pump replaced, and I also got them to replace the thermostat, thinking this would be a simple fix. This seemed to solve the problem for a short time, but within a week or so, the car started running cold again – I should have dropped it back to them, but never got round to it.

So this weekend I replaced the thermostat, thinking it had failed again. The old thermostat did look to be broken, and on running the car on the drive way with the new thermostat fitted, the temperature gauge moved up to the normal half-way position. All looked good until I took the car out some time later for a 5 mile+ drive, and the gauge didn’t budge off the cold. The top hose of the engine was only luke warm.

I’m a bit purplexed now – can there be any other reason for the car running cold, other than the thermostat? Seems a bit unlikely the new (Europarts) thermostat is a duff one. Could there be something broken with the thermostat housing? Ie the thermostat is being prevented from opening and closing?

This is a relatively new problem – the car (winter or summer) used to warm up ok. I think the temperature sensor is ok, as if the car is left stationery with the engine running, the temperature gauge does go up

Thanks chaps

[familyguy1]

I guess the mods will move this to GG or the VW forum so wrong forum to post in I believe, but I had a similar thing on my golf and it was the temp sensor, do you have a good indie nearby who can vag-com it etc and advise on the fix.

[cptsideways]

crud in the system blocking the stat operation? I would say though in my experience aftermarket stats are total rubbish!

[Polome]

You don't say which engine you have. Our 2000 gti had a similar problem after the local garage fitted a new thermostat. This engine has the stat that lies horizontal and it had "fallen" from its housing when being fitted allowing water to bypass it and permenantly flow to the radiator , keeping cold. I fitted a new one , making sure it was seated correctly in the housing. Had to use a thin feeler gauge between engine block and thermostat cover to hold the thermostat horizontal until it engaged with the recess in the cap. Doing this ensured correct sealing between block , thermostat and cap . All worked fine then. Worth checking if you have the same set up. Good luck. Ian.

Edited by Polome on Monday 16th January 13:02

[yeager2004]

Thanks for replies. The engine is a 1.4 16v petrol. The thermostat does sit horizontally, so I guess it could have slipped. There wasn't a lot of room to get in to fit the thing. There's a little pin on the end of the thermostat facing the cap - maybe it's not seated properly.

Since I need to take it apart again, maybe I should invest in a genuine VW 'stat. I'm amazed at the varience between thermostat prices - they seem to range between a couple of quid on eBay, though to £30 for a Gates branded one. No doubt the VW will be pricy...

Coolant sensors seem another part that varies massively too. On eBay, the expensive ones look identical to the cheapo ones. Maybe it's also worth getting a proper VW one.

Thanks

[xjay1337]

OEM components.
Cheap ebay aftermarket tat often fails.........

Gen thermostat and cts It'll probably be fine.

[Polome]

You said the temp indicator was reading cold when the top hose was only warm , this would indicate the temp sensor is responding and probably working ok. I did have a separate problem with my sensor.......if the engine was switched off before fully warmed up I.e. temp gauge in lower quarter the engine wouldn't restart easily and reeked of fuel. I think the temp sensor is linked to ecu somewhere and enriches fuel mix when engine cold . Changing the sensor cured this fault. You don't mention starting problems so I would check the seating of stat first before tackling the sensor. I do concur to comments re cheap parts..vw more expensive but certainly in the case of sensors I would buy oem. Ian

[yeager2004]

Hi - no problems with starting, either from over night stand or having recently driven the car.

It passed the MOT emissions a few weeks back, with all the readings spot on (so don't think it could be running rich on cold cycle)

Cheers