Fault temp gauge?

I've been trying to diagnose my V8 overheating, off and on (mostly off) for the better part of a year now. It's been left alone during a couple busy months at work, but now things are settling down and the evenings are also getting a bit lighter, so I've got more time to tinker.

To summarize: for the first few months I had the bus, the gauge read cool (1/3 from bottom). Then as I was completing a long trip, I noticed the gauge creeping up. Now, the gauge gradually goes into the red within 5-10 minutes from cold start, idling or running along. I replaced *a lot* of stuff (see my older posts), but the only thing that's change the behavior was, for a period of a month or so after I replaced the water pump, the gauge read normally (slightly hotter than straight up). Then it went back to acting up.

I'm coming around to the notion that my engine might not be overheating after all. Among many other things, I replaced the sender (to no effect) and it wasn't until recently that I considered it might be the gauge itself.

So I pose this question to you all: what's the easiest/cheapest way to put in a known-to-be-working water temp gauge? (even temporarily)

And is there anything between the sender and the gauge (wiring? resistor?) that might be causing the problem? That is, if I just buy a new one, what else between the sender and gauge (besides the engine! :doh might give me trouble? I just read about cleaning the earthing strap connections, which I've yet to do.

Suggestions appreciated!

It is just a straight wire between the gauge and the sensor on the block.
Obviously you checked the terminal was clean when you changed the sensor.
Next thing would be to check the wiring behind the gauge making sure the earth is firmly attached.

Now Land Rover temp gauges are ****e they dont really tell you what temp it is so best job is to replace it that way you will know exactly how hot or cold the engine is.
I fitted a Tim gauge with matched sensor a few months ago, a lot better and it only cost about £35.

I am not sure what size the thread is on a V8 but on a 300TDi it is 1/8 npt which the Tim gauge sensor was, but it did come with adapter so i presume one would fit a V8.

Iv gone through this with my 200tdi , took a lot of new parts and even more frustration to find out it was the gauge !
I fitted a mechanical temp gauge And it works with no electrics to go wrong

lr guages in good condition you only need to know where it normall runs all guages should be treated as compariters,you can check temp with proper thermometer and you can fit temp strips ,we use them to check temp on recon engines we build ,just get std guage for year and engine,

I have one of them fancy IR temp guns, but I don't know (a) where to take meaningful readings or (b) what's a normal surface temp for the varios relevant locations. I assume I'd have the same problem with the temp strips.

From memory, the (surface of the) top rad hose was about 85C and the bottom was 75C.

Where else should I measure and what do you reckon a normal temp range should be?

but they do prove you havent overheated ,your gun is about right ,you test in various locations and compare as youve done 85 top hose is about right whats your thermostat 88? considering nothing is completely accurate,since your engine is pressurised you can go over 100 but under normal running what you have isa right ,if worried just check heater still blows hot on run,first sign of overheating engine,is heater blowing cooler or cold

Yep, now that you mention it, the thermostat is an 88C model, which makes the top rad hose reading seem spot on.

jamesmartin said:

if worried just check heater still blows hot on run,first sign of overheating engine,is heater blowing cooler or cold

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Wow. If I understood that correctly, you're saying the heater will blow colder (or colder) when the engine is overheating. I sure wouldn't have expected that. Care to elaborate on why that is?

The heater is definitely putting out nice, toasty air.

EDIT: Just put in an order for a VDO temp gauge, sender, and tach so I should have some measurements to back up my suspicion by this weekend.

this is the thing i fitted TIM 52MM MECHANICAL CAR ENGINE WATER TEMPERATURE GAUGE | eBay UK but got it from local motor factors for £18 . i just liked the idea that it dose not rely on 20yr old wireing

when coolant overheats it expands and is lost through cap,the first thing thats lost is water through heater pipes as they come out of top of head no water no heat transfer. youd be amazed at the amount of people who want head gasket doing and fix heater as its not been blowing hot for weeks

hi james

can you explain this better for me . i have no heat in my landy , garage near me says head gasket ? i cant quite understand the last part of the sentence.

thank you

rokertreeservices said:

hi james

can you explain this better for me . i have no heat in my landy , garage near me says head gasket ? i cant quite understand the last part of the sentence.

thank you

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jamesmartin said:

when coolant overheats it expands and is lost through cap,the first thing thats lost is water through heater pipes as they come out of top of head no water no heat transfer. youd be amazed at the amount of people who want head gasket doing and fix heater as its not been blowing hot for weeks

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basically my head gasket need doing?

No heat is the symptom, head gasket is the fault.

Don't just guess its the head gasket in your case, could be something as simple as heater matrix full of mud!

kavefish said:

Yep, now that you mention it, the thermostat is an 88C model, which makes the top rad hose reading seem spot on.



Wow. If I understood that correctly, you're saying the heater will blow colder (or colder) when the engine is overheating. I sure wouldn't have expected that. Care to elaborate on why that is?

The heater is definitely putting out nice, toasty air.

EDIT: Just put in an order for a VDO temp gauge, sender, and tach so I should have some measurements to back up my suspicion by this weekend.

Click to expand...

The heater doesn't put out cold air because of the overheating - the overheating often makes the engine lose water - and no water in the heater makes the heater stop working.