I've been having an intermittent problem with the temperature gauge in the car going cold when I take it on long drives. I had the mechanic replace the thermostat, flush the rad and replace the coolant and for a couple trips it was fine but now it's happening again.
Any suggestions are welcome as my mechanic is stumped. At 120 - 140km the gauge is normal but get it up to around 180 - 200km and the temperature drops like a rock and I start to get worried about damaging the engine.





Sorry about the last picture, 200km and 1 hand on the wheel.

 

Yep seen that problem here in the extreme heat of the desert climate of the Middle East. It’s what prompted me to R&R the coolant system on my 99 XK8.

With daytime temps at 45degC plus (110degF), I didn’t believe what my coolant temp gauge said on the dash. Too low! So either it was either low coolant levels, leaving the sensor in the cross over pipe in the air, or simply the sensor had gone bad. Recently replaced the temp gauge in my charbroil BBQ as it went bad.... coincidence... I think not!

So I elected to R&R the entire front engine coolant system including a coolant flush and a new cross over pipe with sensor. Haven’t seen the low gauge reading since.

Hope your problem is simpler to fix.... Hmmm.

 

Hi David, thanks for your reply. I can see it being a bigger surprise in the heat you're in. I'll tell the mechanic to order the parts and drop the car off on my next turn around and have him change the cross over pipe and sensor. Hopefully that will solve the problem. I love driving the car and don't mind spending the money but I sure hate worrying about it when something looks wrong.

 

Plug an OBDII data reader into the 16 pin port and look at he the ECM readings?

 

Thanks for the suggestion. I'll whip back to camp after lunch and plug in the OBDII reader and report my findings.

 

I plugged in the OBDII reader and it tells me "no fault codes". I checked the ECM and got some numbers that mean nothing to me but might be related. With the engine warm and gauge in the middle and idling I get coolant temperature at 132 C, down stream oxygen sensor bank 1 is .51v, down stream oxygen sensor bank 2 is .43v, heated oxygen sensor bank 2 is .11v, mass air flow sensor CPU is 1.32v. I got a few other numbers, fuel trims etc. Also checked the coolant level and it looks good. Hopefully this can help someone point me in the right direction.

 

You're seeing 132 degrees Celsius? Isnt that then 274.6 farenheit? Barring a typo that sounds way too high to be safe.
frankly I'd think youd be overheating and blowing hoses if this is true. If memory serves me Steve's RealGuage tops out at 245F. That's the top of the temp scale on the guage.
I hope this means you have a defective coolant temp sensor, cheap part ez to replace. But why your factory guage would not be pegged in the red, with your ac disabled (car does it automatically if above a temp way less than 275F) I cant figure.

Would you mind confirming that you get a 132 degree celcius reading?
John

 

I took the car for a little run and the coolant temperature is 135C. See picture. Could it be that something is wired backwards as the engine does feel hot? I get no fault codes with the OBDII scanner and when I went through the list of diagnostics none of the sensors tested bad.
The hoses look good and the car drives great even when the temperature gauge drops, no strange noises or odd smells and the gauge goes back to normal as soon as I slow down when going through a small town or stop to stretch my legs. Then it won't start to drop again until
I get it up to 140km or so. When I pull over and lift the hood the engine doesn't feel excessively hot, no big blast of super heated air and no bad smells, hissing noises or bulging hoses. By the time I drop the hood and get back into the car the gauge is back to normal. I'm starting to get a little nervous now as I'm 500+ km from home with the car.

 

I can't account for your in dash guage action, but sometimes the simplest answer works. I'd change the coolant temperature sensor.
I had an incident recently where the car started getting up to 240 degrees farenheit. There were noticable drivability issues.
No one else has commented, but I can't imagine that you'd be driving far at 270+ degrees. Especially with these engines so susceptible to overheating damage.

A quick trip to auto parts store, 10 minutes with a wrench and sensor changed.

I admit this goes into a loop when the dash displays a low temp, OBDII shows crazy high temp, but no overheating automatic actions take place.

My recommendation: change the sensor, see what settles out.

 

Right on John, thanks. I'll drive into Smithers tomorrow or Monday with the company truck and grab a new sensor. Hopefully I can find one out here otherwise I'll have one shipped up before I drive the car. Now I have something to do tonight, locate coolant temperature sensor.

 

Just a thought. The thermostat can go in both ways...the right way and the wrong way. (And I don't recall which is which...even the drawings I've seen are confusing.) You might try flipping the thermostat.

 

I was thinking of something like that too but would it cause the temperature gauge to read cold instead of hot? I had the thermostat replaced about a month ago but the problem happened before and after intermittently..

 

John,

Thanks for your help. The car has been sitting turned off for 6 hours now and the coolant temperature reads 98C, outside air temperature 12C. This is only 37C different than when it was running with the temperature gauge in the middle. I'm thinking you're right and the sensor is shot
or the Icarsoft OBDII reader is. What temperature are these cars suppose to run at?

 

The standard temperature gauge gets a lot of flack for being a placebo, but when working correctly it does show if the engine is over or under the correct operating temperature. At 135C the gauge should be pegged at the top, so the problem is more than just a faulty sensor sending the wrong values, the gauge is displaying the wrong values also. This is a table showing what the gauge should be reading versus the engine temp. This is for my 2001 XKR, you would need to confirm the 97 works the same way:-

°C = °F

0-80 = 0-176 - Warm up

80 = 176 - Thermostat starts to open (80°C to 84°C)

83 = 181 - Start of Normal range on Factory Temperature Gauge

90 = 194 - Radiator cooling fans come on at Slow speed

92 = 198 - Normal

94 = 201 - Normal

96 = 205 - Thermostat fully open

98 = 208 - Radiator cooling fans come on at Fast speed

100 = 212 - Normal

102 = 216 - Normal

104 = 219 - Normal

106 = 223 - Normal

108 = 226 - Normal

110 = 230 - End of Normal range on Factory Temperature Gauge

110+ = 230+ - Overheat

127 = 260 - Maximum on factory temp gauge

 

The sensor is in the plastic outlet pipe that runs across the front of the engine. I would replace the pipe as it's not expensive and comes with a sensor installed. Being old plastic, you might break it if you try to just replace the sensor.

 

Thank you very much for your help guys. It's guys like you that keep guys like me on the road. I'll order a new cross over pipe and have it shipped up here. I have 2 weeks before my next turn around and hopefully I can drive the car back rather than bring it home on the back hoe trailer.

 

FWIW
the crossover pipe in the R version costs hundreds- dont have a heart attack:-). The non supercharged one costs the local repair shop $44 around here, I got mine for $75 and was happy. As I recall list price is a bit over $100. Thinking back, it may come with coolant temp sensor installed. Don't forget to ask.

John

 

Thanks John. Would you happen to know the part number? I've been looking at the parts list from the stickies but can't find it. I don't have the supercharged system.
I don't mind spending the money. When I bought the car I figured I'd be putting $500 - $1000 into it each year to keep it running right.

 

Sounds like it's overheating...

Here's an issue relating to replacement parts to check...On the reserve tank part of the cooling system at the top of the engine near the firewall, there are two hoses leaving the tank. On some model year cars, one of the hose tangs is blocked off. That's the hose that goes to the top of the radiator (I'm pretty sure...it's been a couple years). The open hose goes to the outlet pipe at the center top of the engine. Make sure that the open tang goes to that outlet pipe. Confusing the issue, the cooling system can be made to work with a tank that has two open tangs or one open tang. And on a '97, who knows which tank you have. When there are two open tangs, you may (or may not?) have to route your hoses in a certain way.

I would check to see if the hoses have been installed correctly.

 

Ya, I'm pretty mechanically retarded so I'll be taking it in to the mechanic when I get it back to town. I'm going to replace the pipe with the coolant sensor in it before I head back home and hopefully that solves the problem.