overheating GTV

[poohbah]

My '81 GTV has developed a tendency to run pretty hot, including bubbling in the expansion tank like an espresso machine on shut down while dumping coolant out the overflow pipe.

It did it the other day (it was a very hot day admittedly) and reckon I lost about 300ml after turning the engine off.

I have checked the coolant and can find no evidence of oil in it, and have also checked the oil and can find no coolant in it either . No signs of milky brown sludge - I even took a sample of oil from the sump and cooked it in a spoon - no bubbling, crackling or hissing to indicate water/coolant in it, so I don't think the head gasket has blown.

I have also tried to bleed the cooling system in case there were any air pockets. Hasn't done the bubble and dump again, but it does seem to get over 80C pretty quickly and then push up to 90C or more in traffic after much shorter time than normal. But other than that, the car seems to be running fine, and no obvious extra strain.

Any tips? Could it be the rad has some kind of partial blockage perhaps?

[Craig_m67]

Head gasket failure can also (sometimes) allow combustion gases into the coolant .. causing over pressure etc.  There is a product in the UK that can be used to sniff the coolant for hydrocarbons, bound to be something at your local rad / mechanic that can do similar (sniff the coolant for burnt/unburnt hydrocarbons).

Just a thought (this happened with my JTD)

[poohbah]

Cheers Craig, yes my obvious concern is head gasket  but as noted I can't detect any coolant in the oil, or vice versa. No smoke, steam of any  type, and no hissing either. I suppose I should get a compression gauge to test compression, to make sure. I haven't done one since high school, so it might be an interesting experiment! I guess there could be microscopic split so not big enough yet allow fluid past. Really hoping it's just a fixable cooling system problem, not a head gasket since I've just spent a pile buying the GTA and fixing stuff I needed to pass a pit inspection.

[Alfapride]

How's the tuning on the car? All stock? Timing? One thing to check is the fan is wired corrrectly so air pushes towards the motor and not sway from the motor reversing the leads which is easy to do can cause this issue also another tip if you don't have air con connected you can wire both fans in series to run together for some extra cooling benefit goodluck

[poohbah]

Cheers mate, car has standard timing. Next checkpoint for me is the thermostat to see 8f it's stuck in closed position. Couldn't get it off when I tried last week. Interesting about AC. I have disconnected AC and removed the compressor a couple of years ago. The fan for AC is attached in front of the rad  and I don't actually think it is working at all.

[GTVeloce]

First thing to check is thermostat is opening fully.

A simple test for head gasket is to squeeze the hoses while the engine is running. If there is extra pressure the hoses become hard although if it is a very small leak you may not notice.

Possibilities that are easier to fix (than a head gasket!):
Engine tuning
Blocked thermostat
Blockage in radiator
Flush the block and reverse flush the radiator
Check fan operation
Piggyback second fan - if you are not using AC anymore, wire the two from a single relay with the two 87 pins feeding the two fans. If nothing else you will get a better fan outcome because it will now be getting 12V instead of maybe 9V after it goes through all the spaghetti from the fusebox!

[poohbah]

Cheers for that, will try the various suggestions on the weekend. I like the wiring the two fans suggestion, though I may come back with some "how to" questions.

[Colin Edwards]

If the AC fan in front of the radiator is redundant - then remove it.  Its just adding unnecessary mass to the car and getting in the way of air reaching the radiator.  If you need to run two fans to resolve the overheating you are just smothering the real issue.  The root cause of overheating must be found before more damage is done!

[poohbah]

thanks Colin - prior to the suggested rewiring, I had actually been thinking about removing the front mounted AC fan. But it is a PITA to get to.

But regardless, I'm focused on working out the why its started running hot. And thermostat seems most likely culprit.

[GTVeloce]

Ok, front mounted fan I would just dispense with. I was thinking you had a dual (side by side) fan setup. As Colin said, you need to fix the root cause. That said, Perth summer...you probably need all the cooling you can get! My dad has just installed a larger, more modern fan in his Alfetta sedan (also in Perth) to help ensure it doesn't overheat with the AC on.

[carlo rossi]

Now I know this sounds weird
But but a 50grams of fine ground black pepper and put this in the tank ie radiator and run the car at idle til around 85 deg so the thermostat opens
And turn off leave until it cools down
Then drive as per normal
It does work
Ripkeys  believe it or not

[poohbah]

Cheers guys.

Carlo that does sound bizarre, so bizarre that it sounds a bit witch-doctory.

But maybe worth a shot. By ground, do you mean a really fine grind? And would you put it in the overflow/expansion tank? My rad doesn't have a cap of its own.

[carlo rossi]

Yes fine ground black not white pepper in the expansion tank

[poohbah]

thanks mate. I might try it after I've had another go at the thermostat. Ideally would like to fix it properly.

[Paul Gulliver]

I hope this is not stating the obvious, but why wouldn't you just pull the radiator and get it flushed. If its never been done just think about how much gunk is in there after 40 years. I did that on my GTV about 10 years ago . I also took the opportunity to add another core to the radiator. Never had an over heating  problem since including 10 seasons of club sprints