Cooling system queries

[Brenjacques]

Hi all,
I'm getting through a fair bit of the car now and I'm turning my attention to the cooling system which I have a few queries about.

Firstly is the pressure, there was virtually no pressure in the system when I bought the car due to the expansion cap leaking. I've replaced it as it was also losing some coolant from the top.

Now, after a bit of a run the cooling system has a lot of pressure in the hoses. Previous cars I have had have never had as much as this, but the pressure is literally making the hoses almost rock solid. Just wondering if this is normal for the car, it's a 1.8 GTS EX engine. I'm not getting any white smoke or noticable coolant loss, nor is it getting frothy so I think HG is okay.

Secondly is the rising of the temperature. Before replacing the expansion cap it used to sit just at mid way almost all of the time, even in slow moving traffic. Now it tends to rise a bit, as much as 3/4 in traffic turning the fan on which will bring it back to about half way again. Strangely has only done this since replacing the cap, I have a new thermostat to fit but I don't know if the current one is definitely faulty. Maybe it is sticking a bit or not opening fully but I can't quite see how replacing the cap has caused this temp rise.

Other than those problems it's working okay, I'm planning on replacing all of the cooling hoses and thermostat, giving it a flush through and refilling with new coolant but I'm just a bit concerned about the change since replacing the cap. Anyone experienced anything similar?

[mr.brown]

It sounds like you had some pressure issues before and the cap was doing it's job.

Although it's a "pressurised" system it's not a very high pressure - the cap opening pressure is only 1.2 - 1.5 bar so the hoses should never be solid - even at peak temp you should be able to squish them and feel the fluid within.

A stuck shut thermostat won't necessarily cause a pressure build up - just a massive temp increase.

Flush the system as planned - but also remove the rad and reverse flush that. Leave the hoses attached to the engine and run a hose through the top hose as well. Make sure you have the heater slider fully open when you do this.

When you refill, run it up to temp with the cap off to prevent any air locks - until you see a steady stream back into the tank from the rad overflow pipe.

May as well get a decent branded cap if you haven't already.

[Brenjacques]

Thanks for the reply, with the old cap the seal had deteriorated so it was leaking quite badly. I could try replacing this one again and see if it improves anything. As for the hardness of the pipes, I can press them a bit, I'd say they are similar to a bicycle tyre when they are at full pressure.

is it worth getting a head testing kit for the cooling system to see if there are any gasses present?

[Brenjacques]

Hi all,
Just pulling this thread back up. So I did a HG test on the car and it did have a blow from cyl to coolant. It's been in the garage and had the head gasket sorted as well as the valve stem seals, oil and filter change, coolant flush and replace along with the thermostat.

Took it for a drive in not too bad traffic and the engine is still heating up above half way, the needle sitting just a few mm clear past the LED at its worst. The fan didn't kick in but as I pulled it up on the drive it did after letting it sit for around a minute and does bring the temp back down. Pressure is now reduced in the hosing since the hg change bit the temp is still acting the same. With summer now well under way is this just expected behaviour or should I continue trouble shooting. Planning on doing a few long trips this summer and want to make sure it doesn't give me any trouble during this.

I'm going to replace the expansion cap yet again with a known good quality type, any suggestions on which brand I should go for?

Also one bolt is missing fixing the fan to radiator, does anyone know the size of these so I can get one fitted

Cheers
Bren

[GT_II]

The needle a few mm right of centre is normal when fitted with the standard 87 deg C thermostat, so I wouldn't worry about that. The fan would be coming on a lot more if it was overheating.

For expansion caps, I'd go for a genuine one from VW (part no 443121321), as they pretty much last forever, although prices on the internet suggest they retail at around £40.