2000 Pontiac Montana 3.4 Liter Overheating

[schwanracing]

I done a intake manifold gasket raplacement about 2 weeks ago and everything went fine. I replaced thermostat while I had everything apart. Yesterday the guy brought it back saying for the last week(he drives about 25-30miles one way per day) it has started to overheat, and the heater does not work, and he has to put about 1 gallon of coolant in per day.I pulled it in the shop and put my coolant pressure tester on it and pumped it to 15lbs and waited. It held for about an hour without losing pressure and I found no signs of leakage. I let the pressure off but left tester on and started vehicle to make sure engine compression wasnt getting into cooling system everthing was fine. I drove it and found that the temperature was fluctuating quit a bit between about 150-210, but the heater only worked when I held motor over 2500 rpm, and when I held it over 2500 rpm that was when coolant temp dropped. Any ideas?

[roadrunner2]

Possible faulty engine temp sensor.

Perhaps air in the coolant as well.

[schwanracing]

Not faulty temp. sensor, it is actually overheating plus that wouldnt explain no heater, dont think it is air either but I will rebleed system 2 see.

[schwanracing]

OK, I changed out the water pump and it seemed like the van was doing fine. I shutit off and let it cool all the way down then test drove again. This time I got about 3 miles then it started getting hot fast. I got out and opened bleeder valve and got nothing but air out. I took it back to shop carefully took off radiator cap and noticed coolant level was a little low again, so I put my pressure tester on again while motor is around 195F and can find no leaks and pressure again held at 15lbs for about 1 hour. I cant figure out why coolant level keeps going down but I have no leaks or coolant in oil.

[driver540]

See if its going to the overflow tank. If so try pressure testing the radiator cap. Just had one come through my shop like that.

[schwanracing]

I just got done checking that and it seems fine, but I left pressure tester on it over night, and it only had 3 lbs on it when i got to it this morning. I started it and had alot of steam coming out of tailpipe, I went back to smell it and it does have sweet coolant smell to it. Now my question is headgaskets, or intake gaskets again?

[driver540]

Mght want to do head gaskets anyway if youre gonna tear it down that far. Just a few more bolts. Them darn 3.4s are terrible. Got one at shop the owner just did intake on and a few hundred miles later, you guessed it. Good luck. Wish they made more room in the engine compartment. Thats the biggest pain.

[schwanracing]

Now that I take a look at this again there is really no way anyone could mess up the intake gasket to make coolant get into intake RIGHT????It almost definately has to be head gasket/cracked heads. Is there any other components that anyone can think of that might allow coolant to get into cylinder?

[driver540]

I know you probably already have, but check the intake for cracks also.

[schwanracing]

Just got all my parts in today, but it was definately the front head gasket. Sent intake and heads out to be checked for trueness and cracks. Thanks for all the help. The only other thing I need to know is the torque specs and sequence for head gaskets.