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Overheating on Track

Posted: Mon 09 Oct, 2017 2:30 pm
by Gazza
Hey fellas, I've been having an issue that I want to post on here for posterity rather than Facebook.

On Saturday I went to the Mighty Car Mods track day at Mallala near Adelaide.  I had the most fun I've had in a long time out on the tight, technical track and I was a lot quicker than I thought I would be relative to the rest of my group.  I think they put me in the noob group because I hadn't been there before.  I have some video footage to edit and upload as soon as I get the time.

After lunch the ambient temperature started to come up, it wasn't hot but was in the high 20's.  I started to notice my coolant temperature would creep a bit and after 10 minutes on track it was just getting too high so I had to bail.  Easing off for a cool-down lap brought it back down straight away.  This happened on a couple of sessions before I gave up for the day. 

I was talking to a local dude who seemed to know his stuff (he was driving a 400 kW Skyline that he'd built himself) and he sort of said it's common, probably the thermostat etc, all good points.  But I'm not so sure.  I have had quite a bad noise that has been getting worse lately and I put it down to a dodgy idler bearing (the one for the alternator belt).  I got suspicious when I noticed after the second overheating run that there was no pressure in the coolant hoses right after the run, with the engine still running.  I popped the timing belt covers off and the back of the belt is all shiny and looks like it's been slipping on something.  So obviously I'll take the thermostat out and have a look I reckon the water pump is seizing up and unable to keep up with the higher RPM, or maybe the belt isn't tight enough?  Sorry I forgot to take a photo of the belt, I'll do it as soon as I can.  Belt and pump are only about 30,000 km old.

Any pearls of wisdom?  Maybe just hurry up and get the Mivec motor ready?

Re: Overheating on Track

Posted: Mon 09 Oct, 2017 7:12 pm
by box
No warranties  :lol: But yeah, MIVEC will fix it. 

Is it holding coolant or is it losing it?

If it's full of coolant and it's hot, it should be pressurized. Even if the water pump isn't pumping coolant around, it should still pressurize when the temperature comes up. Maybe a radiator cap issue? 

Re: Overheating on Track

Posted: Mon 09 Oct, 2017 8:34 pm
by Gazza
box wrote:
No warranties  :lol:

Haha it's done pretty bloody well, this motor.  It doesn't like the new 15W oil I put in it until it warms up, but other than that bit of ticking in the morning it's never put a foot wrong.
Not losing any coolant, at least not a noticeable amount.  The overflow bottle wasn't filling up.  Maybe you're right, might be worth trying a new radiator cap.  I noticed that the rubber is a little bit munted.

Re: Overheating on Track

Posted: Mon 09 Oct, 2017 8:58 pm
by box
It's a good (cheap) place to start before getting too carried away.

If you suspect the timing belt is slipping on the water pump, you can run the engine with the top belt covers off and monitor the temperature of the water pump pulley - a slipping belt tends to create a lot of heat in the offending pulley. The more it slips, the hotter it gets. 

Re: Overheating on Track

Posted: Tue 10 Oct, 2017 6:36 am
Put a higher pressure rating rad cap on. I think my TT was either 0.9 or 0.6 and it was blowing alot into the overflow. I have an 18 - 125 on my racer which is using a stock NA radiator. I think that means 18 psi and 1.25 bar. put at least a 1.1 bar cap on.

Also what is the condition of your radiator?? Is it really clean and free of bugs and sh**?? how many fins are bent over and constricting air flow (both sides). It's cheap to fix this as well.

Re: Overheating on Track

Posted: Tue 10 Oct, 2017 9:55 am
by magn1t
If it's hot and there's no pressure in the radiator (known by squeezing the top hose), then you've got a leak but not only that, your boiling point is a bit lower.

It's either going to be a faulty radiator cap which is easy to check


The seal on the pump that's gone.

But you need to check for loss of coolant first because any leak anywhere will give a loss of coolant.

Worst case situation is that the head gasket has a leak internally, if it's going to happen, it's going to happen when you push the car hard, cylinder pressure will push coolant out of the cap, when you shut it down, you've lost coolant so there's no pressure in the rad.
The next thing that happens is that due to excessive pressure in the cooling system, coolant gets forced part the pump seal, the bearings rust, then the pump seizes, taking with it all 24 valves.

It DOES happen.

If you catch it early enough, it's an easy fix by re torquing the heads.

Re: Overheating on Track

Posted: Tue 10 Oct, 2017 1:27 pm
by Gazza
Thanks guys, I've got a few things to look at next time I see the car. 

Maybe it has lost coolant, but you can normally spot where it's leaking especially if it's coming from the radiator cap.  There were no drips of any kind under the car between track sessions.