cooling problem

[ohidunno]

Hi all, my usually ultra reliable Chimaera 4.3 has just developed a cooling problem. Yesterday having returned from a 40 minute fairly slow drive I noticed a relatively small amount of vapour coming from under the bonnet. This was coming from the header tank. Unfortunately I was so tired on that last trip that I can't remember checking the temperature dial at all (I think I'm normally pretty good at this but I hade just had a heavy lads w/e in Portugal). I have tested a few basics this morning and would welcome any feedback, please bear in mind that I am no mechanic and the car is due for its annual service but I am a bit worried about getting there (70 miles normally fast run) without breaking down or damaging the car.

Header tank level is 6" from top, too much I know. I do not know the coolant mix.
Inside temp gauge set to cold, blower off
Ran engine at idle with some light revs intermitently. Temp gauge was off the cold end of the scale for about 5 minutes then climbed fast to approx 85 - 90. At this point the fans came on and the temp stopped rising but did not fall.
After 2 minutes the header tank belched another small quantity of steam.
Turned engine off.

Anyone care to chip in knowlege. Is it just a case of poor radiator performance.

Thanks for helping out, Stuart

[GreenV8S]

Maybe the pressure cap starting to weep under pressure. I suggest you top it up (ordinary tap water will be fine if you are only putting in a small amount), take it in to be serviced sooner rather than later and mention this problem. In the meantime check the water level daily and keep a close eye on the temperature gauge.

[shnozz]

does sound like the pressure cap spring is tired. Simple and cheap enough to try that first.

[Chris Smith]

I agree with the above. Try changing the pressure cap.

[PeterC]

I agree with the possibility that the pressure cap is at fault, so check it out. However, may I suggest an alternative in that you may have a small leak in the cooling system, most probably the radiator - the soldered joints are very prone to hairline cracks.

Failure of radiators in Chimeara's is very common, I think it is because the radiator is poorly supported (a couple of thin rubber bushes?)and is as a result subject to heavy pounding from the road. And we all know how poor the roads are these days.

If you have a hairline crack it does not always show under normal pressure testing, only at full operating temp & pressure allied to road use when the radiator will be flexed. You will lose only a small quantity of water but on cooling air is sucked in and it is the air expanding next time you run the car that can blow the radiator cap. Additionally, with a hairline crack the cooling system will never reach the correct operating pressure and therefore can boil.
If I am right you will find in necessary to top-up your cooling system from time to time, so check levels regularly as has been suggested. Failure to check could lead to serious over-heating, cracked and warped heads costing lots of money to fix.

[ohidunno]

cheers all.

I guess it makes sense to order a pressure cap first and monitor water level carefully. Does anyone know of an online parts retailer or the source of the component?

thanks, Stu

[shnozz]

I would have thought you could pick one up down your local Halfwits - pressure caps are all pretty standard dependant on spring rating (15lbs on a RV8??)

someone should be able to confirm

[jonathant]

The blue pressure cap on my '99 Chim is off a Mk1 (or is it Mk2?) Golf. I got one for a tenner at my local VAG dealer.

[mongoose]

jonathant said:

The blue pressure cap on my '99 Chim is off a Mk1 (or is it Mk2?) Golf. I got one for a tenner at my local VAG dealer.

its a very common VAG part,used on several models.I've even seen them on a Porsche Boxter!

[tvrbob]

You are describing symptoms I experienced. It wasn't the pressure cap in my case it was vapour lock. Before buying a new cap just squeeze the top hose on the swirl pot. You'll be able to hear whether its water or air. Vapour lock happens when vapour or air finds its way to the water pump. Circulation stops for a moment and the water in the block starts to boil hence vapour release at the pressure cap.

[verysideways]

Pressure cap is a standard Mk2 Golf GTi part (had the exact same cap on my '89 Jetta 16V).

Odd that your temperature didn't go down once the fans came on though - both my Chims did this, and a recored rad (at £150 inc vat, easy to take out and replace yourself, or an hour's labour if you want to pay someone else) sorted both out like a charm. My 450 with a warm cam will eventually get hot, fans come on (92 i think), and within a minute temp is down to fan off temp (which i think is 87). Leave it to ilde and it's three minutes or so before the fans come on again...

Once you've done the pressure cap and watched for leaks, you may want to think about the rad. Remember that ambient temperature out there these days is way low, wait until June/July when ambient in traffic is 25+ degrees.

Keep us posted!