I have a friend with a strange question he says his 2006 3.0 engine is running cold. He has replaced the thermostat 2 times with no resolve. I have not looked at the car yet and was wondering if others have experienced the same issue.

 

What is the coolant temperature when checked with a scanner? Don't rely on the instrument cluster gauge to display the correct temperature.

 

I just checked it today. The temp on the engine is 185 +/- a few but the ecm and gauge is fluctuating between 150 & 160. The thermostat and temperature sensor have been replaced with the same results. I had my obd plugged in and was showing the same function. He is now going to check the sensor leads to the ecm and have the ecm checked if necessary. It was strange to see this happening.

Gus
JagRepair.com - Jaguar Repair Information Resource

 

Some aftermarket thermostats are junk. This is for all makes, not just Jaguar. It’s got to the point I won’t install a new one without testing it first.

Keep in mind if the first replacement was indeed bad, your friend probably just went back to the same store and got another bad one from the same defective batch.

Did he save the two thermostats he replaced? I’d test those in a pot of water on the stove. See what the temperature really is when they open.

Now that I think about it, what are the symptoms your friend is seeing? Is the gauge not reaching the center position? Remember, the gauge is deliberately misleading, and is centered from approximately 180-230F. As NBCat has suggested, use a scanner for a more accurate indication. And is that indication even accurate? Use an infrared thermometer on the radiator inlet hose to compare.

 

Both thermostats were jaguar. The temperature on the head was at 185f with a lazer temp sensor and was consistent. We did bleed the system before starting today.

Gus
JagRepair.com - Jaguar Repair Information Resource

 

Where exactly are you taking this temperature reading? When I was having some temperature issues on my ‘02 V6, I was initially taking the reading at the thermostat housing.

I learned the hard way that airflow from the fan was skewing the reading. What is your ambient temperature? On a cold day, and with the engine not working very hard, little heat will be expelled from the radiator. With these conditions, the fan may be blowing a lot of relatively cool air.

I found I’d get a lot more accurate reading at the radiator inlet hose, away from the fan’s influence. Of course, the thermostat must be at least partially open, so you do have to consider that. But since you’re dealing with temperature colder than normal, the thermostat isn’t stuck closed.

 

At the left head front and back and left and right of the radiator.

Gus
JagRepair.com - Jaguar Repair Information Resource

 

I’d test them anyway, even if they came from Jaguar. In my sob story, I got a bad replacement thermostat from Motorcraft, part of FoMoCo’s official supply chain.

Then once I determined the temperature reading was also inaccurate (the old two faults at once trick), the first Jaguar replacement was also bad. Talk about a headscratcher!

Do you have resistance/temp specs for your temp sensor? Mine was the CHT version for the early V6, so I don’t think the specs I found will apply.

 

The sensor was changed and still showed the same results. The thermostat was changed 2 times with Jaguar parts with the same results. The temprature on the engine is in line with what it should be at 185f +/- a few.

Believe me I gave a lot if thought thinking in line with you but I think at this point with the irregular readings from what the infrared reading saying the engine says it is to what the car gauge says it is leads me to electrical.

Gus
JagRepair.com - Jaguar Repair Information Resource

 

If I understood this, the OBD shows the engine to be running cold but it is not actually cold.

Could be the ECT, if so. (Or it's not seeing properly moving coolant.)

 

For a quick check of the coolant temperature sensor, let the car sit overnight so the engine is at ambient. Pick a time when the weather is somewhat stable, with no rapid rise or drop in air temperature.

Turn on the ignition but don’t start the engine yet. Hook up your scanner and record the sensor temperature.

If the sensor is reasonably accurate, the coolant temperature should indicate within a few degrees of ambient air temperature. There are no guarantees the sensor will track accurately as the coolant heats up. But if way off when cold, then you know the indication system has a problem.

 

It wouldn't hurt to run a cooling system pressure test. In my over-inflated opinion, coolant flow gets wonky with a minor leak and pressure can't build up to normal. A pressure test will quickly rule out this possibility.

Have you determined whether this is an indication issue or the engine is actually running too cool? Maybe a combination of the two? How is the heater output with HI selected on the control panel?

 

Along with your suggestions I want to check the second temp probe that is designated for the oil and see what it is doing. I did not put it in the equation..

 

Good idea, though I think EOT is not supported in that era OBD so you'd need to measure sensor voltage accurately or use mode 22 (rest of command should be 123d hex).