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Land Rover Repair/1998 Discovery running hot

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Question
John,

My '98 Discovery is running hot, or so it seems, with no other symptoms. At first, it was heating up only at stoplights, etc. So I replaced the fan clutch as I knew my electric fans are running and it would settle back down once I got moving. I did notice something tonight, though - the temp gauge on the dash goes straight to about 1/3 of the white area as soon as the truck is turned on, even after sitting for some amount of time. Then, when started, quickly rises to about 2/3 of the white area, sometimes as high as the top white line, and just hangs there. Have you ever known of a coolant temp sensor to fail in a way that changes it's displayed range?

I can shut off the engine when the gauge is showing high, or top of white range, and slowly remove the coolant reservoir cap without any bubbling over or hissing, or anything of that sort. In my experience of over heating cars, that goes against what I have seen before and almost makes it seem like it is not in fact overheating.

If I were to go so far as aiming a digital thermometer at it, would you have a suggestion as to where to point it and what temp to expect? Any other thoughts or suggestions?

Thanks,
Michael

Answer
I recently had the experience of getting four new temp sensors in a row for an older Rover.  All did what you say - read partway up when cold and all the way hot at normal temp.  Shoot the top of the motor where the sender is located (near the thermostat)   If you read 180-195 the temp is normal.    If you read 220 it's really over hot.  

I ended up solving the problem with the truck here by getting a new genuine sender and putting 50 ohms in series with the sender.

No idea why this has happened

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John Elder Robison

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I own J E Robison Service in Springfield, MA. We are Bosch Car Service for Land Rover, BMW, Mercedes, and other European lines. I can answer most questions about Land Rover service or repair. I'm known as a car enthusiast, machine aficianado, photographer, writer, and speaker. I've been around Land Rovers and British cars most of my life. Visit me at my car business, www.robisonservice.com or my author website, www.johnrobison.com. Check out my autism and writing blog at jerobison.blogspot.com or my photos on www.pbase.com/robisonphoto John Elder Robison

Experience

I have been a Land Rover service manager since Land Rover returned to North America in 1987. My company is a four-star Bosch Car Service facility, known nationwide for Land Rover service, overhaul, customization, and restoration. In addition to Land Rover our company services BMW, Jaguar, Mercedes-Benz, Rolls_Royce, and Bentley motorcars. We have factory-plus-level service capability for all makes. Visit my company online at www.robisonservice.com > service > land rover Also visit my blog at robisonservice.blogspot.com

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ASA IATN NPPA PPA

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In the Land Rover world, my writing can be found in various print magazines and online at robisonservice.blogspot,com. In the wider publishing world, my work is published by 20 publishers in over 50 countries. Mt books Look Me in the Eye, Be Different and Raising Cubby have made US and international bestseller lists.

Education/Credentials
I am ASE certified, Bosch Trained, and trained by Omnitec/T4 and Autologic on their Land Rover test systems.

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