expansion tank overflows without overheating

[carthrills]

Hey All,
I have a '96 9000 2.3L turbo. My coolant overflows the expansion tank periodicaly. The coolant is warm to the touch so I don't think the car is over heating. My temp gauge remains at a cool level without fluctuating. I notice that the tank usualy overflows at high rpms, and sometimes at idle. I don't think it is vapor locked, because it overflows without air bubbles coming out of the hose. Both fans work, and the heater core seems to be fine. This started happing after i serviced the cooling system. The service included a new thermostat (89 degrees) and coolant flush. I can sometimes drive the car for 2 hours down the freeway without it overflowing. Does anybody know what is going on? I am out of ideas. Thanks, Josh

[carthrills]

I have also replaced the cap on the expansion tank with an OEM saab cap.

[benji9k]

Originally Posted by carthrills

I have also replaced the cap on the expansion tank with an OEM saab cap.

Was the cap replaced before or after the problem? Could be the cap in either instance.

Or, perhaps there's blockage downline from the tank and coolant just keeps getting pumped into the tank, but hardly anything flows out, comparatively.

Coolant Flow: Pump -> Tank -> Blockage -> Pump

Higher RPM would make the pump work faster and increasing the pressure, without the flow on the other side to compensate.

Just speculation, but a possibility.

Try a test of idling the car with the cap off, if you've got blockage, a spill would occur, if everything is flowing fine, the would be no bubbleover just at idle. (correct me if I'm wrong here.)

[boxman]

given that you also have oil in your coolant my guess would be,as you've already suggested in your other post, you have a head gasket prob'

[carthrills]

thanks a lot for the help. this site is far better at responding than my 300 member yahoo group. i replaced the cap after the system started overflowing. i think a blockage may be the culprit. it is the only thing i haven't checked. The overflowing started after i replaced the radiator. i bought the radiator used. the guy shipped it in peanuts without covering the holes. i thought i got all the peanuts out. I blew it out with an air hose and ran water through it. the water seemed to flow through fine. The chances are very good that a lone peanut remained in the radiator. however, is it possible that the bad head gasket is causeing the overflow? How should i search out and remove a blockage?

[ferrous_monkey]

Err, Peanuts? Is this a type of packaging product, whats it made of? cardboard, polystyrene plastic?

Mr Monkey

[benji9k]

Originally Posted by ferrous_monkey

Err, Peanuts? Is this a type of packaging product, whats it made of? cardboard, polystyrene plastic?

Mr Monkey

Styrofoam, about the size of a real peanut. Not too good for a radiator with uncapped ends.

[Aussie9000cse94]

I would think it's most likely that the head gasket is blown.

Oil can be forced into the water channels via a break in the head gasket. It's pot luck where the gasket fails. Sometimes the water also enters into the cylinders. The exhaust will be very steamy indeed.
Some oil passages can be at about 3.5Bar (50psi) pressure. The coolant system can at about 10 psi pressure.
What sometimes happens is that the oil enters into the water passages (due to a break in the head gasket) and over pressures the coolant system. This can cause the overflow of the coolant system. The coolant system is designed to release pressure so as not to explode a hose etc.

[ferrous_monkey]

if you still think you have a styrofoam blockage in your radiator, then you can fill it with petrol to break down the polystyrene,then flush it through with some spirit or more petrol. however sticking polystyrene in petrol can have its hazards (like filling your radiator with petrol isn't)
It will make a gunk that shares many properties with napalm!
I think neat anti freeze will do the same job, can't be sure on that though.
Good luck anyhow

Mr Monkey

[djtaylor]

Having had this happen to me, my vote would also be head gasket, it sounds like it has all the characteristics.

Easiest way is to pop down to a garage and ask them to do a "block test". Basically they will check for the presence of combustion products in the coolant.

See here if you want to read a bit more http://www.arrowheadradiator.com/hea..._leak_test.htm

[djtaylor]

Should have added that the other thing it could be is a cracked head.

David.