87 2.9 V6, boiling water away

lauriehurman · #1 07-16-2010, 01:42 AM

Hi Guys

Each time I would get home after a short drive and switch off I would hear the radiator venting steam into the overflow bottle.
I didn't think too much about it, I assumed the radiator cap was not holding the pressure and needed replacing. I just kept topping up the radiator.
I then went on a long motorway trip. When I got to the other end a lot of the water was gone. Once it had cooled I filled it up and did the return trip. Each time I stopped at a service area a lot of the water was gone.
The water pump seemed to be working because the cab heater was pushing out a lot of heat. The temp gauge was reading a lot higher than usual but not off the dial.
I should have removed the thermostat in case that was jammed shut but it didn't occur to me at the time. I have since taken it out and tested it (in a pan of water on the stove) and it seems to work fine.
At one service area I cut a couple of bits from an old plastic oil can and packed out the radiator cap thinking that it was failing to hold the normal pressure. All that happened then was the pressure got so high that the top hose blew apart in spectacular fashion and I had to call the towtruck.
While I was waiting to get rescued I figured that it must have blown one of the head gaskets. I have now just taken the heads off and it's all perfect. There is no damage on the gaskets and no evidence on the heads or block that the combustion chamber has been pressurising the water system.

OK - I stumped. Can you think of what's wrong.
Thanks in advance
Laurie

P.S. There are no external water leaks and no evidence of water in the oil.

Yrac · #2 07-17-2010, 05:49 PM

Just cause your heads "look" good don't mean they are. I'd say you were a little quick to pull the heads but now that you got them off, take them to a REPUTABLE shop and have them checked for cracks (I think it's called magna-fluxed). Get yourself some good new gaskets slap it back together and see what you got.

FireRanger · #3 07-17-2010, 06:01 PM

I'm sure your heads are fine. Pretty sure they're a little stronger than a rubber hose.

I don't think you understand the process by which your cooling system is supposed to function. Doing what you did to it simply made things worse and did nothing to correct the actual problem.

When you were stopping and seeing the water was low, what was the status of the reservoir tank?

lauriehurman · #4 07-18-2010, 01:18 AM

Yea, I think you are right that I was too quick to pull the heads. I wish I had tried to run it without the thermostat because everything is pointing that way.
I've checked the radiator itself and it seems clear. I'm convinced that the water pump is working because the cab heater was pushing out a lot of heat. As far as I can tell the cab heat system bypasses the thermostat.

I had put water in the overflow bottle thinking it was an expansion tank - but of course it's not because the radiator cap cannot suck water back out of it. But the effect of doing that was that i was able to hear that it was pushing out steam when I switched it off. For all I know it may have been doing this for a long time but I had just not noticed. As I said before when I heard the steam coming out I assumed the radiator cap was failing, hence the attempt to "help it out" during the long trip ( a mistake).

Thanks very much for the replies. Any information you can give me about the cooling system would be apreciated because this is the first time I've had this engine apart and I only have the Haynes manual to go on.

Thanks
Laurie

FireRanger · #5 07-18-2010, 07:19 AM

Have you tried replacing the radiator cap? It's a simple $5 part.

Yes, actually it will suck back in from the tank. When you top the cooling system off, you should fill the tank up half way as well. It will expand to that tank as needed and draw back in as well. The cap works both ways. It's a sealed system so if it pushes fluid out from expansion, it will suck it back in when it cools.

IF the cap is defective and not allowing pressure to build up to about 12psi, your coolant will boil and you get steam pushing out. So replace the cap first and report back.

sgtsandman · #6 07-18-2010, 08:06 PM

The system also has to be full for the draw/discharge cycle to work properly. If the fluid in the radiator is too low, it won't draw from the reservoir.