fluxen

A 30 minute drive with boost (moderate), spits about a quart of coolant out of the system, via the pressure release on my AL AST. I'm convinced it's a coolant seal, but is there anything else it could be? The pressure cap is good. TIA if anyone has any other ideas...

Chadwick

iTrader: (12)

That would be pretty normal, the fluid should be going into the over flow tank on the left side of the engine bay as you face it. A quart change in the level of the tank sounds just about right going from a cold engine to a hot one.

Hope this helps,
Dan

fluxen

Well, I can see expansion causing that, but what's happening is this coolant leaves the system, goes to the overflow. But the system never pulls any coolant back in from the overflow. After *every* drive the AST and Water pump filling neck are always down a quart, and often the coolant light will go off. I fill them back up, go for a drive, and it dumps it back to the overflow. This happens until the overflow tank is just way overfilled, and the system itself is always low again. Any ideas?

oddly, I've never seen any oil in the coolant.

fluxen

Help? Any ideas?

RonKMiller

Go to the post "Coolant leak after shutoff" by MILD7. Start reading...

fluxen

Thanks, Ron. Good luck with da nub!

maxpesce

Sounds like a leak in the coolant overflow/return hose - on overflow (warming up) it is ok because it is not pressurized but during cooldown it needs to hold vacuum to draw coolant back from overflow tank - The pressure cap could still be the culprit it may pressure (The spring loaded seal) but nor seall the filler neck and hold vacuum in the return hose (check the upper seal of the cap)

fluxen

Wish it was a leak in the hose, but I've run a new hose to a temp overflow where the battery used to be, so I can watch what's going on. It's pretty clear it's a bad o ring now, it blows more coolant than I think it should out, and doesn't draw it back in because the gas in the cooling system stays in and pressurized.

Oh well, now thinking about engine options, because I might as well have a spare. Too bad I can't (as far as I know) run a 20b on a PFC.

fluxen

Interesting update:

Since I'm running my cooling system at 16psi, I'd picked up a Stant model 11330 cap for the AL AST. Well, this cap has a spring which requires a pretty large amount of vacum (god knows how much 1-2lbs?) before you'll pull coolant back in from the overflow. I choose this cap because a 13psi version working the same way came with the Pettit AST.

Last night out of curiosity, I went looking for other caps, and found the 11331 is the same, except it has no spring for the vacum pull-back. Unless there is greater than atmospheric pressure in the AST to push the vacum valve shut, this thing will vent to the overflow. For the hell of it I gave it a try.

When starting the car, it spits about a 1/2 quart of coolant into the overflow, then pressure builds in the AST and it does nothing. The nice thing is while driving, it actually pulls coolant back in when pressure is below a certain amount. I know this because on certain drives, the level in the overflow will be lower than it was before I left. A nice improvement over my previous situation.

This doesn't solve the whole problem, since there's still a ton of air in the AST / filler neck after my commute to work, but it's better than it was. I'll still need to rebuild, but I can abuse the car a little more now

Just though I'd post the info for anyone else in my situation.

fluxen

Update - when I said I could still abuse it a little more, I really meant a little. The coolant seal deteriorated rapidly, and after about 200 more miles, the leak got bad enough that it would start getting too hot after about 20 minutes of driving, at which point I'd have to pull off, release cooling system pressure, and refill the coolant. The engine is basically done, and I'm going to buy another so I'll always have a ready spare.