I recently replaced the timing cover gasket as it was leaking small amounts of coolant into the oil. As part of that I drained, flushed, and replaced the coolant (Dexcool to Green Prestone), put in a new Genuine 180 degree T-stat, new Genuine reservoir cap, put in new heater core hoses, put in a new throttle-body heater plate and gasket, replaced all of the hose clamps with the screw type hose clamps.

Everything seems to be running fine. I have bleed the system 4 times using the method outlined in the RAVE, each time getting a little air out of the system. After each time I would run the engine (with the reservoir cap on) until operating temperature was met. Then I would drive it anywhere between 5-25 miles at highway speed. After this last bleed cycle, I no longer had the rushing sound behind the dash. I thought the system was good and bleed, so I drove it about 45 miles at highway speeds. No rushing in the dash and everything seemed good. It then sat at my destination for about 14 hours and cooled, I then drove it home again at highway speeds. About 43 miles into the trip (2 miles from home) I heard the rushing sound again while exiting the highway. I just assumed I would need to bleed the system again as there might have been a little air left. I let it sit for 24 hours to cool. This time when I opened the overflow tank, it released a little bit of pressure (it does this every time, not a large amount of pressure, maybe 2-4psi) and the overflow tank level rose to the point that it is spewing coolant out of the overflow hose.

While driving, I been monitoring the engine coolant temp with an ultra-gauge. It fluctuates between 183.2F and 185F. At idle (stop light) it goes up to 189F and stays there, then immediately goes back down to 185/183.2 as soon as I start driving.

So, the temperature seems good.

During the service above I also replaced the wires with 8mm Kingsbourne and the plugs with new champions. Power seems good and there is no white smoke, no misfiring, no coolant leaking anywhere, etc.

I suppose my next step to to test the coolant for exhaust gasses.

Could it be anything else? Could the new overflow tank cap I bought be defective?

 

I let it overflow from the overflow line into a container. Then I bleed the system per the rave again. I measured how much fluid came out during the overflow and how much I had to put back into the system after the bleed and it was virtually the same amount, so I'm not losing any. The engine is running right now with the heater on full. Nice and warm, so I don't think the heater core is clogged.

I don't see any bubbling what-so-ever in the expansion tank.

Once again the temperature reads 183.2F again (according to the ultragauge, with the hood open and idling) and is staying there.

The radiator hoses seem a little stiff, but I have no idea how stiff is too stiff.

I ran it for 20 minutes and the highest it got was 186.8F.

 

when you say you are bleeding it per the rave, your bleeding it cold threw the screw in the upper hose? are you getting air from the upper hose of the in the tank?

 

Anytime you take cap off while warm, you will get overflow. The expansion tank is for catching this overflow. Check level while cold and maybe get front end off ground and run with cap off until warm while bleeding thru screw in upper hose.

 

Yes, bleeding it cold through the bleed screw. i let it cool (overnight usually), raise the tank 8in in the air, take the cap off the expansion tank, then unscrew the bleed screw and leave it open until it's pure coolant coming out, no air.

Usually when I open the reservoir cap, I'll get a small puff of air (maybe 2-4psi). When I open the bleed screw on the upper hose, I'll get some air, then coolant.

When it's running and warm, I'm not seeing any bubbles in the tank at all (like you would normally see from a headgasket combustion gas leak), but something seems to be pressurizing the system slightly.

When it had overflowed, it had been sitting for 24 hours, so should have been cold.

The ambient temperature around here has been fluctuating between about 65F at night to about 80F during the day. How long does it usually take for one of these engines to cool completely?

 

I bled the coolant system again while cold. Got a little air out again. Then I did the test for exhaust fumes in the coolant when cold (while running, but engine cold) and it was negative. I ran it for about 15 minutes, then did the exhaust fumes in the coolant test again and it was still negative. Well that's good I guess, no head gasket leak. I'll probably do another round of tests tomorrow when it's cold, then warm again just to be sure.

Right now the front end of the vehicle is raised as high as my jack stands go (wheels only about 4 inches off the ground) and the coolant bottle is sitting on top of the battery cover.

I must be doing this wrong even though I've been following the RAVE exactly. What a crazy procedure...

 

I have the same issue. Haven't figured out yet. I get enough pressure the over fill tank looks low until I pull the cap. Also slight water in the dash sound. Truck runs fine and never needs more coolant.

 

Yeah, that does sound like the same problem. I bled and ran it last night with the nose raised. I'll probably do the same tonight and continue on that path until I stop getting air out. It might just end up living on jack stands forever with the nose in the air.

Has anyone had any success with a pressure bleeder? What ones work well?