Hi,

 

My car last night overheated and the coolant and water in the expansion tank was boiling and steam was coming out of the top, and there was a lot of it, lost about 2 litres. Now I'm not sure why this has happened, but we found out last week that the car didn't have a thermostat, so put it in the garage and they put one in, then I drove it to college and back the next day no problems (bearing in mind that's a 10 minute drive there). Then the day after that drove it to work which is about 15 minute drive and then drove it back at 11pm so no traffic, and as i pulled up my road as it started overheating leaving a trail of water behind. The temp gauge was in the red.

 

Now I have had no problems at all before, and I know that a car without a thermostat means that the car will run cold constantly, so putting one in will increase the running temperature. But the fan didn't work when it should have done, and the fan worked before the thermostat was in. 

 

I've checked all the hoses to feel if there is a leak or a block and doesn't seem like there is, radiator seems fine also no leaking coming from that, and pretty sure that I haven't blown a head gasket although there was a tiny bit of mayo under the oil cap (i think just condensation as never seen mayo before).

 

I think could be a faulty thermostat? or a blockage that ive missed

 

Could anyone make any sense of this?

Edited 21 September, 201411 yr by shambrook

Sounds like the thermostat is not opening. It's not unheard of for pattern parts to not work properly, but it could be that the little plastic bridge piece has snapped off internally inside the the thermostat housing so the pin has nothing to push against, which results in the stat not opening or only partially opening,

One check you can make is to see if both the hoses on the radiator are hot to touch when the engine is warmed, if the bottom hose remains cold then it's likely to be thermostat or the housing at fault.

The thermo switch for the radiator fan is mounted in the radiator itself, it is on the passenger side near the bottom hose, ironically if the engine coolant thermostat is not functioning then often the radiator fan won't operate because no coolant is being passed round the radiator so the fan thermo switch doesn't 'see' any warm coolant if you get my meaning? You can test the switch by unplugging the 2 spade terminals and using a short piece of wie or a hairpin and join the 2 wires together, the fan should run even with th igniton switched off.

a little bit of mayo type gunk on the underside of the oil filler cap is perfectly normal on these engines, it's just condensation rising to the highest point in the engine and emulsifying with the oil vapour, these engines don't often blow the head gasket unless you cook them up really hot.

You can buy new thermostat housings from gsf for these, they come complete with a temperature sensor and a new stat for about £30, it's a little bit tricky to fit too, it's the same thermostat housing as the polo with aee engine code if you are into scrapyard surfing, make sure you get the one from a manual vehicle, the auto ones are the same shape but have 2 extra pipe unions for the gearbox oil cooler.

Hth.

A few other notes have sprung to mind.

blockages, I think it's unlikely there is a blockage in the system if I'm honest but it might be possible if th wrong anti freeze has been added to th system... Below

Coolant/anti freeze.. You should use the proper vw g12 anti freeze on this vehicle which is a sort of pinkish magenta colour, it's actually an organic acid, you should dilute it using de-ionised water ideally, but plain of tap water will be ok, but more importantly you should never ever mix it with any other type of antifreeze, it is possible for a chemical reaction to take place which forms a heavy goo type sludge in the bottom of the radiator in some cases

hoses/caps... A safety note, you should never undo the top the the expansion tank or disturb any of the cooling circuit whilst the engine is hot, you could get very badly scalded! The basic principle in physics is that a liquid which is in a pressurised container will boil at a higher temperature than normal, so for example the coolant might be happily sat there in it's little pressurised system at say 110degrees celcius, but when you release the pressure by opening the top it instantly boils because it's above the boiling point of a non pressurised liquid. I hope that makes sense.

as above, but the first thing you should do is get back to garage and ask for a fix.

if they put a part from their stock you are entitled to ask for guarantee.

where I live the garage is obligated to put a new part for free.

I hope this applies to UK too.

moral: better learn to fix the car yourself.

it's cheaper even if you have to buy some tools.

Cheers for the information and advice guys

 

It's not the head gasket! Which is a good start

 

I put it in the garage to see what they said, and they were going to change the water pump? Never heard of that fixing the problem before so I've got it back and didnt go through with the work as it was going to cost £200. Would have that been a possible fix? 

But Ii am going to have a little fiddle and see if it is an easier fix, because I believe it is to do with the thermostat as you have said tom

Edited 23 September, 201411 yr by shambrook

This is the thermostat they put in, that's wrong isn't it? 

 

it doesn't look right :/

if the engine overheated without a thermostat, putting a new one will never solve the problem.

you put the thermostat in only after you found the true cause for overheating.

possible causes (check in this order:

- coolant leaks

- foreign objects in coolant circuit

- propeller of water pump not spinning or broken blades

- head gasket

 

I would start with a proper flush as described here: http://www.briskoda.net/forums/topic/328338-thermostat-housing-questions/#entry3944436

Take the thermostat back out and see if it over heats again.

I have and it doesn't overheat

I personally would leave it out then. My felicia never had one in. Never gave me a issue apart from the heaters not getting hot in the winter when on the move. While stationary it was toasty. Start to move it get cool and fast!

I personally would leave it out then. My felicia never had one in. Never gave me a issue apart from the heaters not getting hot in the winter when on the move. While stationary it was toasty. Start to move it get cool and fast!

A sheet of aluminium foil slipped in between the rad and the grille should allow the heater to work in winter (take it out again in summer!).

Learned that trick from my dad when he did it on his Audi 80 back in the 80's.

I have and it doesn't overheat

you said:

1) the engine suddenly overheated when there was no thermostat

2) a thermostat was fitted to 'cure' this problem without any explanation for overheating

3) you took out the thermostat and the engine does not overheat

 

unless you forgot telling us about other prior significant events and/or repairs, logic tells me a foreign object is traveling inside cooling system.

it will get stuck again when least desired.

a new overheating could kill the engine for good.

 

driving without a thermostat during summer is not such a big issue.

but the colder will get outside, the longer will take the engine to warm up.

thus the engine will run longer in open loop with excessive fuel consumption.

by the way, the thermostat you showed us is missing a very important part: the central plunger.