86Shelby
02-03-2019, 08:35 PM
This one has me stumped. Vehicle is an '05 Grand Cherokee, 3.7L with the manual HVAC. The head gaskets and timing components were replaced along with the heads resurfaced about 1 year ago due one HG leaking after overheating.
When the outside air temp is 25*, and engine temp is a steady 203*, the vents will blow only 75* when the engine is at idle yet when the engine rpm is raised to 1500 rpm the outlet temp increased to 135-140*. The engine warms up quickly, temp on the scanner stays a constant 203-204* once warmed up and the system pressurizes quickly. The temp difference between the heater hoses is only 10* at idle with the heater on high.
First thought was the heater core. It was only 4 years old, but figured that was the most likely culprit given the symptoms. Replaced that along with the soft heater hoses & thermostat for good measure. I also cleaned the hard lines from the firewall to the core by snaking a piece of wire through them with a small piece of rag attached to the end. That resulted in no change. None whatsoever.
After that I redid the HVAC relearn/calibrate procedure. It did it's thing, with no codes, and still no change in heater performance.
Thinking it was a flow issue at this point, I replaced the water pump as a last ditch effort. Wouldn't you know, no change. In fact, the temps from the vents lowered a little bit, now I'm lucky to get 130* out of the vents going down the road. I wasn't a big fan of the new pump's impeller design, lots of sharp edges; where the OEM unit appears more aerodynamic if you will.
One thing I noticed while burping the system after the pump change is that the temp out of the vents was 125* at idle. This is while the coolant level was an inch or so low in the radiator and the cap removed. It was about 40* that afternoon. After it cooled down and I ran some errands, the vent temp was till low at idle.
Anyone have any idea on what might be going on or ideas to help diagnose this?
When the outside air temp is 25*, and engine temp is a steady 203*, the vents will blow only 75* when the engine is at idle yet when the engine rpm is raised to 1500 rpm the outlet temp increased to 135-140*. The engine warms up quickly, temp on the scanner stays a constant 203-204* once warmed up and the system pressurizes quickly. The temp difference between the heater hoses is only 10* at idle with the heater on high.
First thought was the heater core. It was only 4 years old, but figured that was the most likely culprit given the symptoms. Replaced that along with the soft heater hoses & thermostat for good measure. I also cleaned the hard lines from the firewall to the core by snaking a piece of wire through them with a small piece of rag attached to the end. That resulted in no change. None whatsoever.
After that I redid the HVAC relearn/calibrate procedure. It did it's thing, with no codes, and still no change in heater performance.
Thinking it was a flow issue at this point, I replaced the water pump as a last ditch effort. Wouldn't you know, no change. In fact, the temps from the vents lowered a little bit, now I'm lucky to get 130* out of the vents going down the road. I wasn't a big fan of the new pump's impeller design, lots of sharp edges; where the OEM unit appears more aerodynamic if you will.
One thing I noticed while burping the system after the pump change is that the temp out of the vents was 125* at idle. This is while the coolant level was an inch or so low in the radiator and the cap removed. It was about 40* that afternoon. After it cooled down and I ran some errands, the vent temp was till low at idle.
Anyone have any idea on what might be going on or ideas to help diagnose this?