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Problems/Service/RepairsIf you have a problem with your HHR, want a tip on repairing or performing a particular service to you HHR here is the place to post!
just a thought but check the upper rad hose and filler neck, my 2007 and my 2011 both developed crack and leaked there. Under pressure at that point, could leak out down in the reservoir
Thank you, Oldblue! Can't believe RockAuto only has the Genuine GM part and it cost more than any other individual part I've purchased other than the battery! LOL I will take it off and inspect it before ordering and might call around some junkyards if I need one. I didn't see any leaks coming from the top when I rubbed my hands around that area while it was leaking, but I will definitely double check around the top of the reservoir and around upper radiator hose right by the top of the reservoir (assuming you are talking about where the pressure cap is). Thanks again!
The bottle appears to be empty? When cold it should be up to bulge in the bottle, no higher. There is a difficult to see mark.
When the coolant gets hot it expands and goes into the bottle, when it cools down a vacuum is created and it gets sucked out of the bottle.
If the bottle is over filled when cold it will overflow when it gets hot.
The leak does not look like it is from the bottle.
The bottle appears to be empty? When cold it should be up to bulge in the bottle, no higher. There is a difficult to see mark.
When the coolant gets hot it expands and goes into the bottle, when it cools down a vacuum is created and it gets sucked out of the bottle.
If the bottle is over filled when cold it will overflow when it gets hot.
The leak does not look like it is from the bottle.
Thanks, donbrew! I "think" it was low on coolant so I was going to drain and fill with fresh after done with the suspension work but the leak started before I had a chance to do the job or check current levels. I will do some more checking around where the leak is to see if I can find it. Thanks again!
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Do you mean this thermostat part? I see several others that have the Rockauto hearts for much less, ...
I always get heat for this, but I'm convinced the Mahle thermostat is identical to the AC Delco. Mahle is an OEM supplier. They look identical. I've posted pics. I've tested them in a pot of water on the stove and they behave identically.
Re: your newest leak, The plastic fitting where the pressure cap goes is notorious for crumbling. If the outlet nipple is cracked, that would explain leaking only when the engine gets hot. A leak there Will also keep the recovered coolant from being drawn back into the system, and air will enter instead.
Last edited by PulpFriction; Jan 7, 2026 at 03:54 PM.
Does the Mahle part have the inner O-ring? That is the part that fails. Temp problems are usually from desk idiots that force 190F or 170F parts on the consumer.
Does the Mahle part have the inner O-ring? That is the part that fails. Temp problems are usually from desk idiots that force 190F or 170F parts on the consumer.
I'm not sure what you mean by the inner o-ring, but I examined both parts carefully and could find no difference.
Yeah I hate it when parts peddlers say stuff "fits," even when it's inappropriate for the application.
Tonight I noticed the coolant reservoir was almost full while the car was idling and it seemed to be slowly filling up more almost to where the reservoir neck is. Yesterday when it leaked I don’t think it was full at all but not certain. I did get it to leak a little in the same place while idling, and it doesn’t look like it’s coming from the top near the reservoir cap or the hose pressure cap. I ran a shop towel all around that area and it was all dry while wet at the bottom of the reservoir Im going to take off the reservoir soon to inspect for cracks. Will the reservoir slide out without having to disconnect the large radiator hose with the pressure cap? I believe I read in another post to remove the clamp holding the small reservoir hose near the pressure cap instead of disconnecting at the bottom where it goes to the reservoir. Does that all sound right?
