05 GXP - No heat at idle - car heats up

[cougarcat454]

Car just started doing this. Daughters car. She said the vents were blowing cold when sitting at idle. Plenty of heat when going down the road. I took the car for a few days. It did do what she said. Temp gauge never left the 200 mark. Went to bring the car back to her tonight. Sitting there idling heat starts to blow cool again. Then for the first time I noticed the temp gauge went to maybe 220 or so, radiator fans kicked on. I decided I would go ahead and keep the car to check it out. As soon as I get going down the road returns to 200 temp gauge and the heat is fine. I got home put it in park. Sit for several minutes. Car stays at 200 and the heat blows hot. Just looking for any input. Coolant level has been fine.
Thanks.

[300sflyer]

The level in the coolant bottle may be normal, but you may still may have air trapped in the system. The gauge going to 220 is a real clue.

[AJT2004]

Also check your coolant level, do not assume it's fine by visually checking the recovery tank. When the engine is cold remove the radiator cap, fill to the top of the radiator.

[cougarcat454]

I kind of figured there must be air in the system. What worries me is how it got there. No radiator cap on these cars/it is on the recovery/overfill tank.

[ddalder]

Also check your coolant level, do not assume it's fine by visually checking the recovery tank. When the engine is cold remove the radiator cap, fill to the top of the radiator.

Normally I'd agree, however he's referring to a GXP with the Northstar engine. There is no cap at the radiator. The only fill point is at the coolant reservoir. It's not an overflow like used on the V-6 Bonneville, it's pressurized and this is where the cap is.

I would suggest trying to purge the cooling system to see what happens. How long had it been operating normally before this happened to start? Any recent work done to the car? When was the last time anything was done to the cooling system (or work where they would have had to open it)? If nothing has been done to the car, it just seems odd that this has started out of nowhere. This suggests something has changed requiring investigation.

[cougarcat454]

Have not had any work done. Bought the car in October. Has been fine up until now. I see no external leaks. Coolant was a bit below full cold mark this morning. Added a bit. Drove it 25 mile to work. Good all the way here. Then sat at idle for about five minutes temp moved to maybe 220 again and cool air out the vents again. Will check coolant level when I get back out of work. Car has 89K on it. Probably going to just bring it to my local mechanic and see what he can find.

[300sflyer]

When I was refilling mine with fresh coolant, I too had air trapped in the system. It seemed the best way to remove it, was to drive the front wheels up on some ramps, and then disconnect the upper hose from the radiator. This then became the highest point in the cooling system. If I recall, I was able to add almost half a gallon of coolant into the system. No more issues after that.

This was after I had the stud kit and new head gaskets installed.... Which is another whole issue. This too cold be the issue with yours.

[CMNTMXR57]

OK;

1) Darcy beat me to it, N*'s do not have a separate radiator cap. The tank is the only point of access and has a pressurized cap.

2) This has NOTHING to do with the ECT's.

3) GM runs these vehicles hot on purpose for emissions purposes. 190* - 200* operating temp is 100% NORMAL! It raising to 220* sitting idling IS NORMAL. The low speed cooling fan is set to come on around that temp.

4) These gauges in our car are not precision certified measuring instruments. They are basically glorified "idiot lights" that operate with a "range". So unless you've got it actually hooked up to a scan tool and you're monitoring ECT's, chances are, that 200* you see while driving is actually around 185* - 190* in reality.

5) If the engine and it's cooling system is operating properly, is at proper levels as indicated on the tank and getting up to proper operating temp as indicated (be it 185* or 220*), this has NOTHING to do with coolant levels or the cooling system! At 185* the heat being blown inside the vehicle will be hot to a human being. At 220*, the heat being blown inside the vehicle will be hot to a human being. As far as purging the cooling system of air, a properly SEALED system will purge itself. That is what the pressurized cap does. You don't need to do squat, other than make sure the coolant level is correct. It'll do the rest. There are no bleeder screws or other means like on the 3800's.

This again, lies in the fact that it is an interior actuator problem that has plagued this platform for now 17 freaking years and plagues OTHER GM FWD platforms also. It is well documented here and other GM forums.

[cougarcat454]

OK;

1) Darcy beat me to it, N*'s do not have a separate radiator cap. The tank is the only point of access and has a pressurized cap.

2) This has NOTHING to do with the ECT's.

3) GM runs these vehicles hot on purpose for emissions purposes. 190* - 200* operating temp is 100% NORMAL! It raising to 220* sitting idling IS NORMAL. The low speed cooling fan is set to come on around that temp.

4) These gauges in our car are not precision certified measuring instruments. They are basically glorified "idiot lights" that operate with a "range". So unless you've got it actually hooked up to a scan tool and you're monitoring ECT's, chances are, that 200* you see while driving is actually around 185* - 190* in reality.

5) If the engine and it's cooling system is operating properly, is at proper levels as indicated on the tank and getting up to proper operating temp as indicated (be it 185* or 220*), this has NOTHING to do with coolant levels or the cooling system! At 185* the heat being blown inside the vehicle will be hot to a human being. At 220*, the heat being blown inside the vehicle will be hot to a human being. As far as purging the cooling system of air, a properly SEALED system will purge itself. That is what the pressurized cap does. You don't need to do squat, other than make sure the coolant level is correct. It'll do the rest. There are no bleeder screws or other means like on the 3800's.

This again, lies in the fact that it is an interior actuator problem that has plagued this platform for now 17 freaking years and plagues OTHER GM FWD platforms also. It is well documented here and other GM forums.

So you think the actuators would be working fine going down the road, but at idle they go haywire? Previously at Idle the car always stayed at 200 on the gauge never budged from that spot and always blew hot air as it should at idle or parked.

Any information on the cross over gaskets would be of interest. Where they are located etc.. so I might inspect. Sounds like they could leak but never leave a puddle under the car.

Thanks.

[cougarcat454]

Checked overflow after work. Right on the full cold mark. Drove home everything was good. Decide to put it in park in drive and let idle. The temp gauge stayed on 200 the whole time. Heat blew hot like it should. Radiator fans kicked in, temp gauge still on 200, never moved above 200, just like it always use to be.

[cougarcat454]

Will monitor overflow tank see if loosing fluid over the next few days. Tank was full after work again tonight. Got home put in park and in few minutes it goes to 220 fans going as fast as they can and barely any heat. When I first parked the fans had kicked in but it was on 200 and heat was good. Once it moved to 220 and the fans kicked in high I just let it sit. Never got any hotter or cooler, heat in car luke warm. I went ahead and pressed the accelerator up to around 1200 rpm, almost right away the temp went down and the heat returned. I then let off off the accelerator and the thing ran right at 200 for 10 minutes straight good heat ect.. I turned it off and came in.

Will see what the fluid level looks like after a few days.

[cougarcat454]

Had car in to shop. Did a pressure check and said it held. Said found no antifreeze leaks. Did say he thought maybe it had a miss when he started it up after the pressure check, but not sure. Pressure test could push fluid in the cylinder and cause a miss. He is not fishing for a job, as he said if it needs a HG job he doesn't want anything to do with it.
I also know I had oil burning off of some place as I can smell it at times. Oil Cooler lines are leaking and he said that he thought maybe the oil sending unit had a drip on it too.

I have seen a write up on how to do the lines. Is the oil sending unit hard to get to and replace? Waiting for a little warmer weather to take a look myself.

Car has not acted up for several days now as far as no heat and temp gauge going up at idle.

[cougarcat454]

Update. Block test on car tested positive for exhaust gases in the antifreeze. Should be able to pick up the car tomorrow. Had the head gaskets done new inserts and head bolts, oil cooler lines were also leaking so had them replaced, also all necessary oil gaskets and seals replaced along with motor mount as well. Should be good to go.