Sorry for the LARGE pic lol!

Ok I watched a youtube video just now...I was metering it correctly.

not sure what your asking Steve. Based on your measurements you failed the second test. Voltmeter should be on and set to DCV 20. Measure the Blue yellow wire to ground and should be no more than 3 volts.

Thank you for the instructions. I WAS asking where to set my ohm meter at for the second test. I'll check that and post it.

Sean

I just tested it again and made sure my Voltmeter was on DCV 20. The reading came back at 4.97

Could this be the reason it's overheating?

Steve, no. It's a sensor. It's telling you the car is overheating. But as you've indicated, you are immediately pulling over and reading temps via your IR thermometer and confirming normal operating temperature. I'm not sure you're overheating anymore. You fixed the thermostat. You indicated that temps are normal. You're assuming that the ECT is correctly telling you that you're overheating.

The code is telling you there is an issue with the sensor or wiring leading to it. Since you're over 3 volts, it's indicating you have a short. Check the wire all the way back the the ECU and make sure you don't have any chaffing or bare wire on the blue/ yellow wire. In other words, fix the short.

You might have a defective sensor. I would replace it if your wiring is OK.


Then, if it's me, I would clear all codes. I would by an ELM327. They plug into the OBD II port. Then you download the app to your phone. The app will give you a constant readout of the coolant temperature.
It's doesn't have to be that brand. In fact, given that the OBD II port is right above your right knee, you may want a shorter one. But ELM 327 is a common one with good reviews and you will be able to see real time temps.
here are some:
https://www.amazon.com/s/ref=nb_sb_n...eywords=ELM327


I'd still fix the ECT, I would have your friend clear all codes , install the ELM device and start over.

Hi Stevet. Any updates on this. It would be helpful for others if you could close it out. We can continue to help if you need it as well.

Let us know.

Closed and fixed!!
 

Sean

Thank you and sorry for the delay in closing this out!

Everything is working fine and I really appreciate all the help that everyone provided to me. It's nice to have such a cool support team when needed.

Steve

What was the fix?

Change the head gasket. It was blown and letting exhaust gases in the water channel.

a beautiful piece of junk
 

Well SLBURNS538,I have experienced everything you have and have flushed or tested everything with same outcome,overheating !

2007 xj8 base model 4.2 liter nightmare.75000 miles.bought with 40,000 miles 2 yrs ago.been garage kept by first owner and me.

been on 2 trips.only driven on weekends for the last year.its been well maintained and babied.

very light white smoke out both tail pipes.block tested it.took 10 minutes for test fluid to turn from blue to green.possible contamination from steam milling around in overflow jug contaminating test fluid.pressure tested system to 120 kpa,gauge never dropped.no water in oil.
took water pump off.plastic impeller looked like new.no sludge anywhere.all cooling channels looked like new.flushed all cooling jackets with water pump off.
nothing out of radiator but clean water.looks like its flowing good through it.no leaks anywhere.runs great,idles smooth.put ear up against both tail pipes not even a hint of a miss fire.
I think rad cap should have let pressure off but didn't.coolant boiling inside resavoir ,made as part of the system.
if it does have blown head gasket how can both head gaskets blow at the same time ? light steam out of both tail pipes.

Coolant sniff test again, compression test. The fluid filled test kits don't always tell you. But if it turned green, I would test again. Old test fluid reacts slow too. I had a truck put me thru the ringer with a bad head gasket. HC test did not show HC during tests. This ended up to be as it only really pressurized the coolant system with a loaded engine. It would idle all day and run perfect around town at 35 mph. Coolant pressure test was holding pressure, but cylinder pressure took it thru the roof. Remember that cylinder pressure is way more than 20 psi in the coolant system. Try a cylinder compression or/and leak down test. Are you sure it's not airlocked?