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Discussion Starter #1
The coolant gauge reading is fluctuating intermittently on my '97. It seems to top out at ~87 then drop to ~55 then back up to ~87 degrees. It is most often at 87 degrees but I do notice it drop on most drives. It has been bled properly to the best of my knowledge (top of engine coolant pipe and bleed screw on top of radiator). Coolant tank cap is new.
What would do this? I'll be pulling the plenum shortly to clean it up. Should I change the gauge sensor while I'm at it?

Cheers :)
 

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Discussion Starter #3
Hi David. The thermostat was replaced last month when I did the water pump and belts. Correct one sourced from JAE.
 

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Was it doing this before you replaced the thermostat? What else was done before this started happening? BTW, the radiator must also be bled. Plug on the top left side.
David Teitelbaum
 

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Discussion Starter #5
I'm not sure if it was doing this prior - when I got the car I figured I may as well do the thermostat and WP when the belts/pulleys were done. I did bleed the rad on the top left side.
It's almost as if the signal to the temp gauge is coming in intermittently. Changing the switch and checking the wiring when I have the plenum off is a start I believe?
 

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Is it possible you impacted some wires? FYI I would replace temp sensor while 'you're in there' but it doesn't sound like that's the issue.

My car is substantially different from yours (87 Turbo Esprit) but I was replacing a Bosch CIS injector - absolutely no real connection involved to my water temp gauge.
But after replacing the injector, my water temp gauge was dead; then it zoomed all the way to max, then dead.

After a few days waiting for a new injector, I replaced new injector and now my water temp is 80C (where it should be) then zooms to minimum 50C; swings to max 140C; swing back to 80C.
It is 'alive' but highly inaccurate. The cooling system has been uneventful since 2017 since last rework of hoses/thermostat. And the car is driven about ~1700 miles/year.

I have NO IDEA what I did - I did remove/replace Otter switch wires, but that should not have causes this issue. My guess is the sensor coincidentally went haywire (there's nothing involved with a mechanical fuel injector that should even REMOTELY impact a water temperature gauge.

This reminds me of the broken 'voltmeter' - it started reading inaccurately for months. I used a digital voltage in the cigarette lighter socket to monitor it. Then after nearly 1 year, it magically started to work correctly - no change to the voltmeter. It's freakin' bizarre.
 

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Wingless Wonder
1988 Esprit Turbo
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shinrai perhaps you are low on ^^^. :oops:


But all kidding aside, if you just had cooling system service, you may need to top up coolant (even if properly bled). Is the overflow bottle half full (cold)? It is in the RR wheel well...and you MIGHT think there is coolant inside, but it is only scum inside the bottle fooling you...

Or, there is a wire pinched when the plenum was reinstalled...seems to be a common V8 issue.
 

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You say it has been bled properly "... to the best of my knowledge". Did you do it or did someone tell you so? For a quick diagnostic I would start with engine cold (meaning sitting over night) and check the coolant level in the overflow tank in the right rear wheel well. I have found reaching in and placing a small flashlight directly against the bottle makes the level quite visible. Start with the coolant at the indicated level. Drive the car until warmed up and recheck the coolant level in the overflow. My experience is that if it is above about half way from the cold level to the top of the bottle when hot then there is almost certainly still air in the system.
 

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2007 Lotus Exige S
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What temp thermostat did you use? Does the temp just go back down when driving? If you idle will it hold at about 87?
 

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Hook up an OBD2 scanner and see what the ECU is reading. I tent to trust the ECU temp sensor more than the temp sender for the gauge, they are not the same sensor.

That will tell you if you actually have a temp issue or not,
 
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