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Temperature gauge reading high


dave88sw
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Hi,

I've got an ongoing problem with my series 3 2.25 petrol.  The temperature gauge needle wants to sit just below the red section of the gauge, well above the "N".  It definitely isn't getting hot, i can comfortably hold the top hose while the needle is telling me it's about to boil over, i can drive for over 50 miles and it doesn't overheat and i've checked with a laser thermometer that the engine itself isn't getting hot.  It never loses any water, the fan belt is tight and it's had a recent coolant change.

In an attempt to cure this issue i have:

Changed the voltage stabiliser for a solid state modern replacement (fuel gauge works perfectly)

Checked the earth attached to the gauge unit

Added additional earths between bulkhead/engine and engine/chassis

Checked the cleanliness of all connection on the wire between the gauge and the sender unit

Changed the sender for multiple different brands (tried genuine, intermotor etc, all the same)

 

I've owned this car for 15 years, since i was 14 years old and unfortunately, this issue is preventing me from driving it, i can't stand looking at the gauge telling me it's overheating.  I've considered fitting an aftermarket gauge and sender, however, i really don't want to just work round the problem, i want to fix the original.

 

Any help would be massively appreciated, i'm at my wits end with it. 

Thanks

Dave

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The only thing you haven't changed is the gauge...

How quickly does the gauge go from cold to overheat? If you just leave the engine idling, does the gauge go to the red? If its a matter of minutes, then its more likely to be a duff gauge. With all that cast iron and water in the engine, there is no way the engine can produce enough heat from cold to make the gauge go to red in less than 15 to 20 minutes (or actually at all if everything is working as it should).

Does the gauge very slowly go to red, or rapidly? The latter would suggest an electrical fault.  What temperature does the IR thermometer show on the thermostat housing? Are you doubly sure you haven't got an airlock - do the heater hoses both get hot? From cold, leave the cap off the radiator, does the same thing happen? Does the radiator get evenly hot from top to bottom when the thermostat opens?

 

Edited by simonb
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Thanks for the replies,  I had guessed it was probably the gauge, but i guess i was quietly hoping it wasn't (they're over £100).  I'll report back if i actually manage to sort it out as it would appear others have had the same issue.

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1 minute ago, dave88sw said:

Thanks for the replies,  I had guessed it was probably the gauge, but i guess i was quietly hoping it wasn't (they're over £100).  I'll report back if i actually manage to sort it out as it would appear others have had the same issue.

The sender resistance readings are out there so you can test with a known resistor or two to see if it reads right if you've got any kicking around.

The little 3-way gauge sections come out individually so may be available cheaper on their own - in fact I've probably got one kicking round I could send you if you've got a way of identifying the correct part.

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I’ve just ordered a selection of resistors to experiment with if you want to hold fire on forking out on a gauge just yet?

 I can let you know if they make any difference or not. With mine, I’m still using the series gauge and sender but it now reads much higher than with the 2.25 which used to sit in the normal range.

With the V8 it sits just under the red line at normal temperature so I’d like to bring the needle down a bit but still allow it to rise if the engine gets hotter and the fan kicks in.

 I’m not even sure if V8s run hotter internally than a standard engine??

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@Bigj66 The V8 sender has a different resistance to the Series sender so you'll always have that problem - a single resistor won't properly fix it as it might be (say) 50 Ohms out at 0 degrees C but 10,000 Ohms out at 100 Deg C, so you can't really "fix" it, at best you can make it sit at the right reading for one particular temperature but it'll be steadily more wrong the further away it goes from that temperature.

It's a fairly easy fix with electronics :ph34r: but you need to know the curves of the two senders.

A modern V8 will run on an 88 or 92deg stat which is perfectly fine, running a cooler stat just makes everything less efficient it doesn't actually improve cooling.

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9 hours ago, FridgeFreezer said:

@Bigj66 The V8 sender has a different resistance to the Series sender so you'll always have that problem - a single resistor won't properly fix it as it might be (say) 50 Ohms out at 0 degrees C but 10,000 Ohms out at 100 Deg C, so you can't really "fix" it, at best you can make it sit at the right reading for one particular temperature but it'll be steadily more wrong the further away it goes from that temperature.

It's a fairly easy fix with electronics :ph34r: but you need to know the curves of the two senders.

A modern V8 will run on an 88 or 92deg stat which is perfectly fine, running a cooler stat just makes everything less efficient it doesn't actually improve cooling.

Mine has the series sender fitted John.👍

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15 hours ago, Bigj66 said:

Mine has the series sender fitted John.👍

In that case it may just be running hotter than the Series gauge expects for "normal" - maybe try the "tropical climates" sender if there is one, I know some models they changed sender and/or gauge to move the "normal" point.

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17 hours ago, FridgeFreezer said:

In that case it may just be running hotter than the Series gauge expects for "normal" - maybe try the "tropical climates" sender if there is one, I know some models they changed sender and/or gauge to move the "normal" point.

I’ve never even heard of those, will take a look 👍

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It is possible to adjust the gauges. There are two slots in the back. usually behind little cork discs - one for the high reading end and one for the low reading end. There's meant to be a special tool, but they can be adjusted with a screwdriver. Think carefully before adjusting though, this should be the last option, and only if you're certain that everything else is correct. And if you do go this way be careful - adjusting them they're only thin pieces of tin(?) so they bend very easily.

Dan

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11 hours ago, dra890 said:

It is possible to adjust the gauges. There are two slots in the back. usually behind little cork discs - one for the high reading end and one for the low reading end. There's meant to be a special tool, but they can be adjusted with a screwdriver. Think carefully before adjusting though, this should be the last option, and only if you're certain that everything else is correct. And if you do go this way be careful - adjusting them they're only thin pieces of tin(?) so they bend very easily.

Useful info, especially if someone's willing to post him a spare gauge to have a play with ;)

@Bigj66 I'm away next week but if you want to PM me your addy I'll dig through my box of bits and see what I can send you when I get back.

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I’ve just fitted a 10 ohm resistor in line with the sender feed and it’s brought the needle down to mid point on the gauge from the red. I’ll keep an eye on it and see how it works at different temperatures.

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Sorry for the slow reply, i get very little time to play with my series, i'm in the middle of a V8 conversion on my 110 😅.

Fridgefreezer, that's a very kind offer, i might take you up on it if i have no luck fiddling with the current gauge.

Does anyone know what the sender resistance readings should be? That seems like the logical next step.

I did find a previous thread on the same issue, one suggestion was using a 9V voltage regulator instead of the 10V solid state replacements available, what are peoples thoughts on that? 

 

Thanks

Dave

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