I've got a 2009 Chevy 2500 hd with the LMM duramax with 166.000 miles on it. I let sit outside idling to warm up on a cold winter night and came out to coolant dripping out from underneath it. I have since changed thermostats twice with the second time going back with genuine ac delco thermostats. Ever since that night I have been fighting this thing with it randomly pushing coolant out of the lower vent of the coolant recovery tank. ( I mean I could go 7-10 days without it doing anything wrong) I have replaced the coolant recovery tank, the thermostats, the lower radiator hose assembly, the line coming from the oil cooler up the back side of the engine on the drivers side that at one time looks like it went to the EGR Cooler which has been deleted, I have replaced the radiator, the water pump and the fan clutch also. The engine never runs over 210, not getting any coolant in the oil, I did the EverTough Combustion leak test and it didn't show any signs of a blown head gasket. Since it is deleted the line coming from the oil cooler now connects directly to the heater core, I pulled that line off and wasn't getting any coolant up to the heater core which I believe also supplies hot water to the top of the engine. When I pulled the line off at the oil cooler the water was hot so I thought maybe the rubber part of that line had collapsed, hence why I replaced the line. I will get the low coolant alarm in the dash of the truck, I usually let it cool down 2-3 hours and I will go out and slowly screw the cap loose and it releases pressure it bubbles up fairly well and once it is done the level is a little low so i will top it off. As of Thursday 1-22-26 it has pushed coolant out that recovery tank vent 3 times and now its back to not building any heat again as the temp gauge stays on 160 and there's no heat in the cab at all again. I have been dealing with this for a little over a year now and I'm still just not 100 percent convinced yet that its a head gasket.
LMM issue
- Thread starter Cyounger
- Start date
^^^ yep.
You can prove it to yourself by splicing in a coolant pressure gauge. GM has a spec for max operating pressure and how much it should drop overnight. I did this when I was hemming and hawing about it being a possible head gasket. It was. Super tiny failure.
You can prove it to yourself by splicing in a coolant pressure gauge. GM has a spec for max operating pressure and how much it should drop overnight. I did this when I was hemming and hawing about it being a possible head gasket. It was. Super tiny failure.
Sure sounds like it's time to do a head gasket job based on the parts you've replaced. Probably not the news you wanted to hear but all symptoms point towards it.