New to this forum, so I hope this aint old repetition.
Ive got a new VDO CHT gauge on my 78 campervan with a 2 litre CJ engine and the other day whilst driving up and down the motorways and hills of England with outside temperature around 50 degrees fahrenheit, the CHT temperature readings were as follows
GUAGE READINGS
410 deg slow driving at 50mph on flat motorway
425 deg driving at 60mph on flat motorway
450 driving up slowly in low gears up steep hills.
375 deg coasting at 50mph down hills.
375 deg sitting at idle during gentle city driving
The bloke that emmissions-tested the van (Called an MOT here in England) reckons that the engine's in good shape and theres nothing wrong with it, and temp guages make one paranoid. Hes been working aircooled for 30 years knows his stuff and is a sound bloke.
Despite his advice with these temperatures coming in excess of 400 degrees I decided to check the guage calibration. Basically, with the spark plug sensor sitting in the air temperature of 50 deg the gauge reads 150 deg F and when I drop the spark plug sensor into a boiling kettle it jumps up to 310 deg F. (isnt water supposed to boild at 212)
?So is it a fair assumption to say that every reading the guage is knocking out is actually 100 deg too high? Or is the sparkplug reader meant to read 100 higher to put a guess at the temperature inside the head?
?If the guage is 100 degrees out at 50F and at 212F, then is the guage going to be 100 deg out at 350F assuming the error behaves in a linear fashion not exponential?
?If the guage is 100 deg out then the following readings would be the actual temperatures, do these readings seem normal?
CORRECTED READINGS WOULD ACTUALLY BE...
310 deg slow driving at 50mph on flat motorway
325 deg driving at 60mph on flat motorway
350 driving up slowly in low gears up steep hills.
275 deg coasting at 50mph down hills.
275 deg sitting at idle during gentle city driving
? Can I stop shitting myself about cooking the engine and drive faster say taking the actual temp upto 400 which would be 500 on my guage?
? Can you adjust the calibration on these VDO guages, so I dont have to do any bloody conversions!
Any advice/ answers to these questions would be greatly appreciated.
THanks
Dave
cylinder head temp and dodgy VDO measurement.
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daviehunter
- Posts: 2
- Joined: Wed Apr 06, 2005 2:22 am
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dstar
- Posts: 3733
- Joined: Tue Feb 25, 2003 12:01 am
Your gauge is reading about 100 degrees F too high.
This can be caused by bad connections, or using the wrong
leads to the gauge. It has to be the correct type and gauge wire.
How is it wired to the gauge? Are the connections clean or are they
degraded?
Purchase the correct $17 lead.
The sender isn't calibrated to go as low as ambient temps, so any reading
below it's designed operating range would be highly errorneous!
I think it it's operating range is between 200-600F.
Cheerio!
Don
This can be caused by bad connections, or using the wrong
leads to the gauge. It has to be the correct type and gauge wire.
How is it wired to the gauge? Are the connections clean or are they
degraded?
Purchase the correct $17 lead.
The sender isn't calibrated to go as low as ambient temps, so any reading
below it's designed operating range would be highly errorneous!
I think it it's operating range is between 200-600F.
Cheerio!
Don
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daviehunter
- Posts: 2
- Joined: Wed Apr 06, 2005 2:22 am
For convenience I have it connected to 2 wires that are part of a wire kit called trailer wire (Thats wire of the same size as the the correct $17 lead cable it came with, but contained in a 7 wire cable) dont know about the quality of the wire and its connected with small screw connectors.
This may sound dodgy but what I would say, is that I was concerned the wires would show a difference when I fitted the trailer cable instead of the correct $17 lead cable, so for this reason I ran it at idle using the corect $17 lead, and I then ran it using the trailer cable, in both instances the idle temperature was 375 at the time, so what ever way its wired its producing the same idle temperatures as the correct $17 dollar lead it came with.).
This may sound dodgy but what I would say, is that I was concerned the wires would show a difference when I fitted the trailer cable instead of the correct $17 lead cable, so for this reason I ran it at idle using the corect $17 lead, and I then ran it using the trailer cable, in both instances the idle temperature was 375 at the time, so what ever way its wired its producing the same idle temperatures as the correct $17 dollar lead it came with.).
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500LbGorilla
Those meters are so sensitive to variations in environment and the senders can be a bit flaky too. When you test for boiling temp, it's best to get the water hot, and get it away from the heat source, and then dip the ring in the water, keeping the rest of the wire as close to ambient as you can. They create small voltages based on temp differential. When I say small voltages I mean really small. So small that all it takes is a little EMF to change the reading.
When you don't have any wire connected to the meter, does it drop all the way down?
It would be interesting to see what you got with a different sender, but that costs money, and unless you have a way to try another one, it's hard to say. It sounds to me like the sender itself might be the cause.
Mine works pretty well, I get about 200+ in water and it sits all the way down when everything is cooled off. My head temps run about 300 fully warm with my 2332.
When you don't have any wire connected to the meter, does it drop all the way down?
It would be interesting to see what you got with a different sender, but that costs money, and unless you have a way to try another one, it's hard to say. It sounds to me like the sender itself might be the cause.
Mine works pretty well, I get about 200+ in water and it sits all the way down when everything is cooled off. My head temps run about 300 fully warm with my 2332.
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500LbGorilla