Overheating 2001

[CMFan]

Hello, I have a 2001 Pontiac Grand Prix 3.1 with AC (though I rarely if ever us the AC), approx 166,000 miles. Did not purchase from dealer-ship.

It started to overheat no long ago we have tried almost everything, and to no avail. Here is what we have tried.
Changed the Thermostate (more then once, one was defective)
Changed the Hoses
Bled the system
Tested the fans (by jumping)
Bypass
Water pump still good (from what we can tell)
Heater core looks good

We are not losing antifreeze (we checked it isn't going down)
Nothing floating in the antifreeze
We see no leaks anywhere that we can see to the naked eye.
We check the oil and it all looks good

A relative has a little meter thing that said a plug was fouling the #2 plug (if memory serves me right) so to be sure and when the check engine light came on (on twice) we took it to Autozone and they got a no code. Which is confusing cause of the plug.

We recently took it to Sears garage and had a pressure test done, and asked them to do a Radiator flush (thinking it might be clogged) that didn't work, and their diagnostics showed no problems with the car.
We called them back and they had us bring it back for a new pressure test, they said that there was some brown stuff in the antifreeze (which I am sorry but I can't see it floating in there as they said), that when they flushed it the old antifreeze had geled at the bottom and was probably blocking it from leaking in. They sent us to a GM dealer to by "No Leak coolant sealant" tablets (the five in a pack) Sears proceeded to crush them and put them in, saying this would get us by and shouldn't overheat.

Well it's still over heating many days later, it doesn't peg out but it gets close to the red line. Now here is the catch.
When it gets up that high it will drop sometimes on its own, or
If you floor it, turn a corner, hit a bump, put it in neutral and razz it. Then it goes down to 200 or so. When the temp goes up you lose heat, when it comes down you get heat.

We haven't tried to deal with the intake or head gasket as that is our last resort due to cost and such. The garage [Sears] didn't look to see if that was they said "we are guessing it could be one of those two things, and we don't do those".

Before winter we drained the radiator (all looked fine no discolor, etc) we didn't use Dexcool (we heard bad things about it) then we put in the green stuff (pure, not fifty/fifty). Sears Put back in the fifty-fifty.

Sometimes it will go to the red mark, sometimes it will go to 210, Sometimes it will happen in 5 minutes of starting, other times 15-30 minutes, now according to the manual when it overheats or attempts to it will cut from 6 cyc, to 3 cyc on one side, then when that gets warm it will go to the other 3 cyc until it cools down and kicks back to 6.

We don't know if it could be a sensor, or what have you. None of this makes sense and the gauge is fine, but we can't figure out what to do, I priced what it would cost to do the head gasket or intake and it ranges from $500.00 to $1700.00 I don't have a garage which is why I have to price it.

Can anyone help us? I love this car, and up until this started it ran perfectly, no problems whatsoever. I think I got everything we did and learned down here. If I think of anything else or if I can answer any questions (that might lead to something I forgot to add) I will do so.
Right now this is the only vehical we have and we drive with caution, but I have to get this fix. And we are out idea's.

[HotZ28]

Very detailed explanation of the initial problem and subsequent issues! When the 3.1 overheats to a certain point, they usually develop a hairline crack between the combustion chamber & water jacket. When this happens, the pressure test is useless, because the crack expands with combustion heat & the combustion pressure overcomes the coolant pressure; thereby, adding heat to the coolant. You can have the coolant tested for combustion gasses, or you could leave the pressure tester on the radiator until the engine is hot and see if the coolant pressure increases beyond what the cap is rated for. If the pressure increases beyond the cap rating, it will open and divert coolant to the overflow. The coolant temp does not have to be in the red zone for this process to happen, it is simply based on the system pressure. If the coolant gas test proves positive, time to pull the heads. If # 2 plug is wet looking, it sounds this is like the likely culprit. Remember, when you shut the engine off, combustion pressure no longer exist; however, coolant pressure will remain on the system for a period of time, which usually injects coolant into the combustion chamber through the crack, hence the discolored/fouled plug!

[tblake]

Pull #2 plug out and take a look at it. What color is it?

When you say you rev it and the temp goes down, makes me think there is air getting in the system.

Are you sure the coolant isn't leaking out? What does the underside of the oil cap look like? Slimy sludge on it?

Take a look down under your throttle body and on the other side between the power steering pump and the LIM. Any seepage?

When your car is cold and you start it, does the radiator hose get hard immediatly on start up?

You could also have a shop do a leakdown test on your cylinders and listen for air bubbles escaping from your radiator.

[CMFan]

Okay here is what we have...

Originally Posted by tblake

Are you sure the coolant isn't leaking out?
Don't seem to be, radiator level doesn't move.

What does the underside of the oil cap look like? Slimy sludge on it?
No, it's clear, normal.

You could also have a shop do a leakdown test on your cylinders and listen for air bubbles escaping from your radiator.
When we took it to sears we asked for a full diagnostics everything if you will, wouldn't that have been included? If not I will have to find someone to do that. I don't have a regular shop most the time we either handle problems ourselves or relatives who know more about it do. But no one has this type of equipment.

Take a look down under your throttle body and on the other side between the power steering pump and the LIM. Any seepage?
Did not see any.

When your car is cold and you start it, does the radiator hose get hard immediatly on start up?
No, and idling it went to 210 and we kept checking it didn't get hard, when it got warm enough for the thermostat to open the top hose callapsed, after it cooled down the hose went back to normal. Also when checking you could feel the coolant following through the hose.

Originally Posted by tblake

Pull #2 plug out and take a look at it. What color is it?
We are trying to get the plug out, it is not cooperating at the moment, and we don't want to take a chance on busting the wire or the plug.

[tblake]

The hose collapsed? Is the radiator cap in good shape? Is the overflow hose or resivore plugged up?

#2 is the one farthest towards the front (radiator) on passanger side, right?

Twist the boot back and forth with your hands to break the connection and then it should pop right off. They are stubborn.

[CMFan]

Okay here we go..

Originally Posted by tblake

The hose collapsed? Is the radiator cap in good shape? Is the overflow hose or resivore plugged up?
Cap is in good shape. Not plugged up.

#2 is the one farthest towards the front (radiator) on passanger side, right?
Yes, that is correct.

Twist the boot back and forth with your hands to break the connection and then it should pop right off. They are stubborn.
Will give this a try it is a tight fight with the motor mount right there..

[tblake]

Oh yeah that is right, I forgot that darn mount in the way on the 3100.

You could try and grab on with a pliers and gently twist back and forth or I have always had good luck using a long flat head screwdrive and prying outwards on it from where it meets the spark plug.

If you happen to mess it up, I am sure I have a spair #2 wire from a 60k 3100 set that I messed up #4 and ended up buying a new set.

[tblake]

Bob, Rich, what causes a radiator hose to collapse? I've never seen that before.

[CMFan]

Originally Posted by tblake

You could try and grab on with a pliers and gently twist back and forth or I have always had good luck using a long flat head screwdrive and prying outwards on it from where it meets the spark plug.

We will give it a try, as soon as we can swim out to the car lol. Between the snow melt and the rain it's just a little to wet right now to try.

[andretti]

Originally Posted by tblake

Bob, Rich, what causes a radiator hose to collapse? I've never seen that before.

Bad rad cap not allowing normal venting from the return bottle. When hot, system expansion forces coolant into the bottle past the cap. After it cools down, expansion "normally" draws the fluid back in from the bottle. The bad non-venting cap creates a vacuum in the cooling system.

[tblake]

Originally Posted by andretti

Bad rad cap not allowing normal venting from the return bottle. When hot, system expansion forces coolant into the bottle past the cap. After it cools down, expansion "normally" draws the fluid back in from the bottle. The bad non-venting cap creates a vacuum in the cooling system.

Good to know. I thought the Cap would have something to do with it.

[CMFan]

Originally Posted by andretti

Bad rad cap not allowing normal venting from the return bottle. When hot, system expansion forces coolant into the bottle past the cap. After it cools down, expansion "normally" draws the fluid back in from the bottle. The bad non-venting cap creates a vacuum in the cooling system.

Except wouldn't that have been found in the pressure test they did (that I mentioned in the first post)?

[BNaylor]

Originally Posted by CMFan

Except wouldn't that have been found in the pressure test they did (that I mentioned in the first post)?

Normally yes. But inexpensive part to replace just to be sure.

Does this Vin "J" 3100 V6 still have the original LIM gaskets?

[CMFan]

Originally Posted by BNaylor

Does this Vin "J" 3100 V6 still have the original LIM gaskets?

As far as I know, the owners before me didn't change it, lets just say that they got rid of it because it needed a new Springs, traction bar and rotors and calipers, front brake line, etc. That is the only reason they thought it would cost to much to replace. Wasn't all that bad. After all the fixing was fixed it ran great no problems what so ever until as I mentioned in the first post it just started to overheat.

[CMFan]

Anyother idea's on this. I know I am thinking of taking it to a GM Garage (a dealers garage) they said they could do diagnostics (ie pressure, electrical, etc) for about 60 dollars. Not thrilled paying for another testing but I am not entirely sure anymore that Sears did do anything that was worth 139.00 (rounded off) dollars. No leak Coolant tablets not included in price.

Recently we had to go to a doctors appointment, when we checked it before we left and at one point when stopped before the appointment (gas ect) the antifreeze was normal. But after we got home from the appointment several hours later (the car didn't move from the time of the appointment till we left), the antifreeze level went down half, thing is we don't know where it went. It wasn't on the ground (a caution thing I look for things like that when I leave a parking space it was dry and clean), and it wasn't coming out the back, and the oil looks good. No leaking to the eye under the hood.

We added more Coolant and we are going to check it this morning.

Before if it got hot we pulled over to cool it and you could hear it boil back to the reservior like normal, not its not really doing that like it should sometimes you have to remove the cap to get it to do it. so its more of a which will it be.

I really don't want it to be head gasket or intake .. what gets me still is when it gets to 210 or a tick or so above (before the last line) if you turn sometimes right or left, or hit a good bump the gauge drops. Mixed with all that I mentioned through out the thread. I am about ready to.... ugg