We have a 2006 X-Type 3.0 liter that is giving false overheating alarms. The check engine light comes on, and within 5 or 10 minutes, the gauge is pegged and the red light turns on. We pull over, stop the car for a few seconds, restart the car and everything is normal. Rinse and repeat until we get where we are headed. I replaced on of what I believe are two coolant sensors, but wasn't able to find a second. The suggestion has been bade to me that the thermostat housing contains the second sensor, and replacing the housing and thermostat will correct my problem.
Any feedback as to whether this sounds reasonable?


One more thing: Occasionally, after the check engine light comes on and shortly before the coolant gauge pegs, the car will briefly shake-it feels like running over the wake-up grooves on the side of the road. It's been suggested to me that this is related to the computer thinking the car is overheating.

Any feedback would be most welcome. Thanks!

 

It's unlikely to be overheating as it couldn't cool back down again in seconds. Nevertheless, a thermostat change might be worth a try. Non OEM thermostats in UK have a particularly bad reputation!!

The only sensor for the coolant temperature and gauge is the one right at the top of the engine, between the two cam boxes. It has a Blue/Yellow wire and a Black/Green one. Is that the one you changed?

If the ECM thinks the engine is overheating, it will limit engine speed. Your vibration could be the limiter cutting in, depending on engine speed at the time.

 

The sensor I replaced is the same you describe. I'll go ahead and replace the thermostat. Many thanks astromorg, for the feedback!

 

scotott: Just spitballing..... Is there sufficient coolant in the reservoir?

If the coolant drops below the bottom of the reservoir, steam forms at hot spots in the engine and collects around the temperature sensor - a high point in the coolant loop. Steam is hotter than liquid coolant, so the temperature gauge quickly spikes in the instrument panel and to the ECU. When the steam bulb collapses, the temperature reading quickly drops back to normal.

As astromorg notes, the entire engine can't quickly heat up and cool down. But a pocket of steam forming and collapsing around the temperature sensor can create that appearance.

It wouldn't surprise me that the high temperature reading could cause the ECU to go into limp mode, limiting engine RPM, perhaps causing the shaking sensation. When the steam bubble collapses, the temperature reading returns to normal, the limp mode ends, and the shaking stops.

Again, just spit balling. If someone has a better theory, please share it.

There is a second temperature sensor, but for oil, not coolant. Steam pockets won't form and collapse around the oil temperature sensor. It's to the left of the oil filter, on the output (high pressure) side of the oil pump.

 

The coolant level was on the top of the list for me to check. All is fine there. Interesting information regarding the steam build up. Strange things can have considerable impact on a vehicle's operation.

Many thanks for the input, dwclapp!

 

scottott: Again, just spitballing again (& the mouth is getting dry).....

If the coolant is weak, i.e., heavy on water & light on antifreeze, it will form steam more easily. Water boils at a lower temperature than antifreeze, so dilute coolant is more prone to forming steam bubbles in the engine. Just a thought.

Also, is the coolant system holding pressure? With the engine warmed to normal temperature and turned off, wear safety glasses, cover the coolant bottle with a thick towel and wear a thick leather glove. Very slowly and carefully loosen the top of the coolant reservoir just a 1/4 turn or so. You should hear a significant hiss of pressurized steam releasing from the coolant system - like opening a new 2 liter soda bottle. If you don't hear the hiss of steam being released, it's possible your coolant system is not holding pressure, e.g., the reservoir cap might not be forming a tight seal. If the coolant system is not holding pressure, steam pockets could form more easily inside the engine. Again, be very careful if you attempt this. Steam can burn you quicker than you can pull your hand away and jump backwards.