Grrrr, arrrgh, overheating, waaaah, and VR6

[Funkster 0]

'lo all.

 

I know there's a lot of threads about this and I've posted myself before, but I'm having a bit of an I-hate-my-corrado stress right now and I need help!

 

Driving home tonight, it was -1°C outside. No-one should have trouble cooling in that. However, my gauge was creeping up past the stat temp and by the time I was nearly home was about to go over 90° even though I was just pootling along at 50. After arriving home and shutting it down, I found water piddling from the header tank, the top rad hose quite easy to hold, and the bottom hose cooler than that. The heater had been fine the whole way back.

 

When I got the car the stat was duff and it would creep up like this, but the garage put a new stat & housing on, and it seemed to be sorted. Is it likely to be another duff stat so soon? This was december last year, and I've not done 2000 miles in it yet.

 

I half suspect the water pump, although changing to a lower gear (to throw more water around) didn't really seem to help. Maybe ever so slightly. Every so often the temperature would suddenly drop 5°... I noticed this a couple of times when going round roundabouts but that may be a coincidence.

 

Oh, last thing to mention... it gets to 100 very quickly in traffic, despite having fitted a new thermo switch in the radiator. I know people say this is normal, but the switch is supposed to kick in at 92, right? Also having arrived in a parking space with the gauge reading 100, there was no run-on fan. I have tested the operation by shorting across the connector and found it to work just fine.

 

I know I just need to strip and inspect the whole cooling system as I have no faith in any of it now, but any other support would be greatly appreciated!

 

Back in my manky, cold, slow, left hand drive MGB tomorrow!

--

Olly

[Funkster 0]

No thoughts? Anyone?

 

I'm quite enjoying rear wheel drive again, I just wish it made the VR6 noise )

 

Cheers,

--

Olly

[Henny 0]

change the expansion tank and tank cap... Also check that the little hose from the expansion tank to the top hose hasn't got any blockages in it...

 

Sounds like a classic expansion tank/ tank cap problem to me... 8)

[Kevin Bacon 5]

Other than the water peeing out of the tank, your temps sound normal to me mate. You should only ever panic when the needle goes into the red, it's just that people see the numbers on the guage panic unduly. They're not that accurate anyway. Compare the coolant temp on VAG-COM to get the REAL reading and then look at the guage!

[Funkster 0]

Aye, VAG-COM is on my wish list. However, it's in no way right that the temps should creep up when crusing along in cold air.

 

I shall investigate the piping on the expansion tank.

 

Thanks,

--

Olly

[Henny 0]

if the expansion tank (or cap) is leaking, the temps will rise MUCH quicker than when it's a sealed, pressurised system. ANY leak on the coolant system will cause temp rises like you describe... ;)

[Funkster 0]

I'll bear that in mind Henny, cheers for the info. However, it hasn't been leaking up to now and when I shut it down the cooling system was definitely pressurised, if the feel of the rad hoses is anything to go by. It was just overflowing due to heat soak I guess.

 

Thanks for the support, I'll have it to bits at the weekend and check everything out.

 

Ta,

--

Olly

[Henny 0]

if it's overflowing, you have a leak... otherwise, how would the water overflow?!? ;)

[exturbo2003 0]

if it's overflowing, you have a leak... otherwise, how would the water overflow?!? ;)

err the cap has a pressure relief valve built in

 

check the rubber washer on the tank cap as this can cause overheating when driving.

[Henny 0]

yup, it does, but it shouldn't leak unless it's under some pretty serious pressure which you'd only get when the water is VERY hot...

 

That's why my first reply was to replace the expansion tank and cap... ;)

[exturbo2003 0]

ok i agree just that the seal goes and the valve can wear and let off early so like you say new cap at least

[Funkster 0]

Mornin' all,

 

I've done some stuff and some investigation, and I'm still a bit puzzled. I drained the system and checked the header tank & pipes, and found that the small hose from the top rad hose to the header tank was blocked, or as near as dammit. I blew it out with the compressor, and although it remained a bit restricted (is this in purpose?) it does at least flow a bit now.

 

I flushed the system with some ungent, cleaned it out with water, and refilled with 40/60 G12+/water through the top hose, letting the level stabilise and topping it up before putting a new cap on the header tank.

 

Hoping for the best, I took it for a drive but yet again it started creeping up past the 'stat temp. This time there was no overflowing or change in the header tank level, so that was probably the blocked hose causing that. If I leave it to sit, the fans come on when the gauge on the dash is showing 100, and the after-run fans seem to do the same.

 

So far I have these ideas:

 

1) it's the stat not opening all the way, causing the temp to creep up and the temp in the rad to be lower than the temp in the engine (hence the fans coming on at 100 not 92).

2) the gauge is inaccurate, but not all the time - it stops warming up at the 'stat temp and stays there for a bit - could engine bay temp cause the 'gauge reading to rise?

3) Something's still blocked

4) The water pump's knackered. With the header tank cap off, the coolant is clearly flying around the system when I blip the throttle as the level in the tank bobs around.

 

Other empirical evidence... it doesn't matter if you drive it at 60 or 100, the temp creeps up just the same but doesn't get higher the faster you go. After sitting in traffic and it goes to 100, it's *very* reluctant to come back down again, and generally sticks at 90 for a while on its way down. It never reaches 80 again - 85 is the best that it'll do.

 

Any hints would be great - next weekend I'll take the 'stat out and boil it. If it's not that, I'll be hoiking the engine out to do the water pump!

 

Thanks,

--

Olly