Temperature Gauge Odd Behavoir
Help please. 463- 300GDL 1991. I remedied coolant issues successfully by replacing water pump, belt, tensioner, pulley gearing, radiator & thermostat some 10,000kms ago, and achieved a sweet running engine at 82-90 degrees, Now each time after warming up to operating temperature my gauge goes a little mad. It rises erratically sometimes to 120degrees (the engine is cool) holds and drops to the true 85 then ratches up, holds at 105 etc. After 10 mins of this theatre, with no prompting it falls back to around 85 and stays like this until I say stop for fuel, when hot, and the same charade repeats itself. Wiring or sensors or other? Any advice, thanks Tombo
I remedied coolant issues successfully by replacing water pump, belt, tensioner, pulley gearing, radiator & thermostat some 10,000kms ago, and achieved a sweet running engine at 82-90 degrees, Now each time after warming up to operating temperature my gauge goes a little mad. Tombo
Hello tombo,
From your description, it seems that since your work as described above, you have not done any work on the engine recently, for this problem to have manifested.
If, this were the case, I would ask of you to check on a cold engine, firstly, if your coolant level is correct. If so, then I would suspect the thermostat to be developing a fault, in which case you will need to replace the unit.
Start your engine and let it warm up. Taking care of your fingers’ amongst moving parts, carefully, sense by hand the temperatures around the cooling hoses, are these warming up, as they should do?
Feel the heater matrix hoses, are these warming up as the block temperature (turn the heater temperature up, inside the cab for heating to follow through those hoses). Check the top radiator hose, is this warming up? This should get warm only when the thermostat opens after meeting its first temperature rise. This heat should then transfer to the radiator headers, these should start getting warm too relatively. Feel the pressure build up in the hoses by squeezing it, there will be some pressurising but not rock hard! This is indicative of a head gasket going, where you want to start looking for oil contamination in the radiator (CHECK ON COLD ENGINE ONLY). You could be suffering coolant loss also.
When the engine and radiator are warmed up. Switch off the engine and feel the radiator core, you should have consistent heat radiating across the whole surface area of the radiator face. Any cold spots would indicate core blockage. In which case, this fault will have to be addressed; replacement core is a cheaper option.
If the hoses do feel excessively pressurised and the warm hoses do not get ‘red hot’, then it is temperature sender unit a fault.. This will be the sender unit with a single feed to it and a blue top. Try disconnecting one lead at a time on the sender and check the temperature gauge reading, if the right one has been disconnected, then the gauge will not register at all.
Good Luck.
Regards,
Yha,
If thats the case, seems your sender unit is faulty. Water loss, as you have described, is fine.
Regards,
Dare I interject and suggest the dear old "G" Wagen seems prone to temperature guage "foibles"
My 1984 was & is erratic as well
But hey I just ignore it
And keep an eye for melting/bubbling paintwork on the bonnet
A much better system
Thank you marcus,
Your suggestion is very welcome.
Regards,
Hi Rakesh, new temp sender fitted and guess what, defective, no temp registered at all so had to reverse the operation. Old sender has longer brass element and black plastic- says 120oCmax; new stubbier and red shows 100oC. Merc rechecked and claim correct replacement. any comments? thanks Tombo
Gents
Again i had the same problem on my 290. After a lenghty period at the dealer and changing the sender and no improvement on the problem they suggested i change the instrument cluster. Now i have initially noted to them that a possible cause could be loose earthing wires which they confirmed to have checked. To make a long story short i received the vehicle back from them and the next day, checking the vitals preparing for a long trip i noted that the earth braid from the engine to the chassis (RHS) was dirty and definely not touched in a long time. I felt it - voila! - it was loose on the chassis. I tightened it and also found the battery earth to be loose - after this no more erratic temperature readings
I hope your solutions is as easy as this
Regards
Freek
Freek
Typical dealer response
Thanks
M
Freek
Typical dealer response
Thanks
M
Well Lucky him! At least they did not suggest he changes the frame, or the bodywork, or both :shock:
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Hi Rakesh, thank you so much for your fullsome reply. I have checked the engine warm up from cold and all seems quite perfect. No coolant loss (only 1 cupful in 5000kms), no pressured hoses and a gradually warming rad. The temp gauge needle once it starts moves quite rapidly and erratically up and down, not through heat. I will test sender as you propose and report. Thanks again. regards Tombo