Oil temp gauge issue

[210bhp]

My 356 B has a gauge problem. It’s been like this from my purchase. The car runs well and there are no overheating issues.

I’m beginning to think I may have the wrong gauge, wrong wiring, faulty temp sensor, faulty connection, bad earth etc..


So the gauge in its ‘resting’ or ‘off’ position is like this




When I turn the ignition to the ‘on’ position this always happens,




Next position to ‘crank’ and throughout all running the gauge needle never moves and stays in the second position.


Where should I check first please?

Regards
Mike

[Lightweight_911]

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I seem to remember there were 2 different temp sensors which acted in different ways - one increased in resistance as the temp went up & the other decreased.

It could be that you have the wrong version fitted.

Also new 6v temp sensors weren't available for some time & used originals commanded high prices, so owners sourced/fitted alternative brands which often weren't compatible.

I would contact/speak to PRS ...

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[210bhp]

Thanks Andy. I was hoping Mike might reply here as it’s nice to get some expert information up on DDK for anyone else in the future.

It’s pretty obvious that the gauge and the sensor are not compatible but I wasn’t sure if it was the wrong gauge or wrong sensor (or possibly the wiring) but you would guess the sensor. Thanks.

Did the gauge on your car look like mine? I believe there are more than one type.

Regards
Mike

[Lightweight_911]

Did the gauge on your car look like mine? I believe there are more than one type.

Mine was a 'C' (& also 12v) but the gauge was almost identical - differing only by having 2 additional warning lights in the centre circle.

There were many versions of this combi gauge - some with numbers for the oil temp & some with just a graduated scale ...

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[neilbardsley]

So a bad/no connection is what causes the temperature to move to the right so I don't think the sensor is connected to the gauge. First check that is just hasn't come disconnected. At the back of the gauge and more likely the engine bay (happened to me). If that doesn't solve the problem. I would connect the gauge directly to earth. Under the dash. It should return to the starting position. Then check again at connection between the sensor and wire. That should help you find the short or disconnect.

Next is the question of why the starting position if top dead centre. Here I suspect your gauge is at fault. You can have it rebuilt but that should be matched to the sensor

Sent from my 22011119UY using Tapatalk

[210bhp]

Thanks for your input Neil. So, you suspect wiring or the gauge. Andy suspects the sensor. Looks like there’s no short cut, need to check everything.

Thanks again both

Regards
Mike

[210bhp]

Well, time flies.
Just a further update for anyone interested. There were obviously two or three different possible issues but I initially decided to point the finger at the gauge rather than the sensor. Andy was right, either of these for a 6 volt 356 is a pretty expensive so I did a lot of reading first and every reference suggested that the gauge was not correct for my car and hence possibly not compatible with the sensor. So the search started for a ‘correct’ gauge…..
You all know the difficulties with second hand parts, who to trust, working or not, condition, secure shipping, location in the world, correct dare stamp(!) price etc. hence the reason it took a while to find one.

So, I fitted the gauge after checking the wiring, earths etc. and it works! (Phew). Now I need some help from other 356 owners please. I think I might have got somewhere but I’d like to be sure. The new gauge as Andy pointed out has no numbers, just a sliding scale. After a few local runs and some idling the needle which starts fully to the left at ‘zero’ moves to the following position (sorry about the reflections on the photo) but does not move any further to the right.




So the question is, does this look like the usual position of the needle under normal running conditions with this type of gauge on your car?
I had expected it to be more ‘middle ish’ but maybe not. If this is not the normal position then maybe there are still problems to discover.

Thanks for any help.

Regards
Mike

[Nine One One]

There was this post on DDK which helps with the resistance of what the sensor should be.
viewtopic.php?t=60432


Neil will be taking his 356 engine apart (soon) can he lend you his sensor to test with your gauge?

Failing that take the sensor out, wire it up, remembering to put an earth on it, as it would be earthed via the engine block, and see what the gauge reads with the sensor immersed in boiling water. Ideal oil temperature is around 90 to 105 degrees so boiling water should move it a lot further along the gauge?

Rule of thumb on VW air-cooled engines used to be if after a run you could take the dipstick out and hold it between your fingers momentarily without getting burnt it was running fine. (The bottom bit that goes in the sump)

[Lightweight_911]

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Mike - position of the needle will obviously depend on what type of driving (& speed) you're doing - plus the ambient temperature conditions.

Here are a few comments about oil temps that may help:

Highest I have seen is 3/4 up the gauge, whatever that is, on the Nurburgring at the DDK Euro trip..it was very hot weather at the time. Usually it stays on the left side of the gauge, on UK motorways etc., which I have read is where it should stay most of the time.

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In normal driving for me the temp is between a 1/3 and 1/2 way. The hotter the day the higher it goes!

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[210bhp]

Thanks both of you for your thoughts.
The weather has been hot in Scotland recently (believe it or not!) and on my shortish runs in these conditions I expected the needle to climb higher. However, before I investigate further I’m intending to do a long ‘spirited’ run this week while the weather remains warm and see what happens.

At least I have a clock which seems to be working with the sensor (in line with those two quotes Andy) which the previous clock wasn’t.

Thanks for the replies and links. Appreciate it.

Regards
Mike

[roy mawbey]

Mike,
My original temp gauge from 1959 has in my driving only ever reached around 1/2 way along the scale when driven in the summer and on trips over about an hour long. On my trips out these days its sort of normal to be just over 1/4 along the scale.
Never ever seen it at 3/4 ! But I am a slow old bloke now !

Roy

[210bhp]

Thanks for that Roy. I appreciate it.

I was out yesterday for a longish run and the ambient temperature was low 20’s and the needle was no higher than in the picture above. However, I’m not yet convinced the reading is a true refection of temperature because if I pushed the engine a little harder the needle remained absolutely fixed in that position. I would expect a small variation in needle position as the engine works harder over several miles. It appears that the resistance looks to get to a max point and sticks. I’m maybe coming round to Ian/Andy/Neils position that the sender will have to come out for testing.

Meantime with more digging on t’internet i found this,

[VCG]

You could purchase a heat sensor gun and check the temp by directing it at various places ((I use the oil filter housing first) immediately after a run and whilst still ticking over.
This gives what I think is a great indication of actual temperature and approx what temp is indicated on the gauge. I had great fun, when I first got a sensor, looking at the temperatures in various areas of the engine, and found that they were always running around 60ish to 80ish degrees depending on the ambient temp.
The ambient temp will have quite an affect, our '60B normally runs between the 'normal temp and starting to get too warm' marks shown here. Last week, on a roasting hot day on a long fast run, it got to around the 'starting to get stressed' but I was not concerned, she was singing along.
V&S

[210bhp]

Thanks for that reply. Interesting method which you say is fairly accurate. If you point the gun at the metal oil filter housing I wonder if that directly matches the temp of the liquid oil inside.

Thanks for your experience with the needle position. From what you say it would appear that yours moves each side of the rough centre of the scale during normal running depending on ambient temp. This is what I expected before I connected up the replacement gauge so it confirms that I might not be quite there yet.

I notice from the history file that a new sender was purchased for my car from Rose Passion in 2020. I checked it was the correct 6v item (which it is) so it looks like someone has been grappling with this issue before.

Thanks for your help.

Regards
Mike

[Hugo 356]

The currently available new 6v senders have a diferent calibration to the originals. You need to have the guage re-calibrated to match the current sender or better still get a working old sender