Temp gauge issues: engine, electrical, thermostat or something else? - JeepForum.com
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post #1 of 3 Old 09-24-2021, 07:06 PM Thread Starter
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2005 WK 
Join Date: Sep 2021
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Temp gauge issues: engine, electrical, thermostat or something else?

I'm trying to verify what might be the problem, and if I can fix it myself, before possibly getting scammed by mechanics before paying them a minimum of $3000:

Less than 2 months ago I bought a 2005 Jeep Grand Cherokee V8 4.7L with 153,000 miles.

At this point in my life I do not have the option to "just buy another car." I either fix this car myself, open a credit card to pay an auto shop, or I don't have a car.

The start of the issues:
- Check engine light came on 1 week ago.
- While driving from Berkeley CA to Santa Cruz CA, the temperature gauge kept jumping very close to the "H" each time I touched the gas pedal, and the AC stopped blowing cold air for about 20 mins, then started working fine again. Outside temp was between 69-76 degrees.

Auto shop tests and results (unsure if I can trust all of this due to the details I've noticed, listed below):
- Found code P0301 and confirmed cylinder misfire.
- Checked compression, good at 145PSI.
- Moved spark plug and ignition coil to different cylinders and the misfire stayed on cylinder #1.
- Performed leak-down test and the cooling system started bubbling in the radiator during the test.
- Performed hydrocarbon test and the cooling system has 600+ hydrocarbons in the overflow tank, indicating an internal engine leak.

Today, as advised by another mechanic over the phone, I checked the oil and was supposed to check the radiator coolant because he said those are the telltales of the problem being the head gaskets:
- Oil dip stick was fine, translucent brown color in the marked “safe” margin level
- Could not find radiator coolant reservoir or anything coolant related to the radiator besides a big hose, only the main coolant reservoir, which is a little over full from getting topped off at the mechanic’s on Tuesday and is a yellow-green color

I also:
- Turned car on and sat there for 20 mins w/o the temp gauge going up much more than slightly above the fully cold edge
- Drove the loop around the neighborhood which goes downhill then uphill on the way back. When accelerating on the uphill it jumped from 1/4 to 1/2 mark. Returned, parked, kept it running, engine sound changed to sound a little different as it sat there idling in park and I watched the temp gauge go quickly from 1/2 to 3/4.
- Last night, once it was cold out, I drove it 1 mile out and 1 mile back, and the 1 mile back was almost all uphill, and the gauge did roll from the 1/2 mark to a little beyond the 3/4 mark.
- No different colored exhaust smoke since purchase
- No leaks on ground since purchase
- No visible leaks under the hood
- No odd sounds since purchase, minus what sounds like the AC belt in front of the passenger seat clicking for 10 seconds randomly when AC is on (only happened 3-4 times)

So maybe the issue is electrical or the thermostat and not the head gasket/engine?

Sgerritzen is offline  
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post #2 of 3 Old 09-24-2021, 08:25 PM
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2009 WK 
Join Date: Dec 2016
Location: Salem
Posts: 58
I can't imagine it is anything but the head gasket if you had bubbling in the coolant system on a leak down test. I had the 4.7l in my WJ and did the heads on it. Not too hard, especially the driver side. Getting them properly torqued is a little tricky since it uses a torque plus angle method.
Barra is offline  
post #3 of 3 Old 09-25-2021, 01:52 PM
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2005 WK 
Join Date: May 2014
Location: Stamford
Posts: 1,425
Do a leak down test on Cylinder #1 to see if it is just the head gasket or possibly the valves too. That will also give you and indication if anything broke inside of cylinder #1.

If it is just the gasket, great. There is a special torquing sequence you need to know and you will need new head bolts, a new and very good head gasket, probably the head resurfaced, and probably timing chain tensioners.
RCS1300 is offline  

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