Can you trust the dials? (Square dash) - overheating/oil pressure

Outrun944 · Nov 30, 2010

Hey guys,

'85 LUX (not a 85.5) with a square dash ... I'm wondering how trustworthy the dials are.

1) Temperature
I'm mostly driving in evenings when its getting dark with lights on. I've noticed, after a while driving and say you get stuck idling in traffic - temperature always rises - but after being stuck for a long while in bad traffic or a 'spirited run' the needle is getting near towards the red. The main fan DOES come on and work fine, I had the fan checked over when I replaced a thermo fan switch. On my old 944 it used to come on at the 3/4 mark then temp would drop below the 1/2 mark eventually - now its nearly at the red zone when that happens. HERES THE KICKER - I had pulled over and switched off my lights - the needle nearly jumped down a whole quarter from past the 3/4 mark down to the 1/2 mark!
LOL - so what do I trust? Lights on or lights off? hehe! OR do I have fault electrics?

2) Oil Pressure
Strange fluctuations. It should be at 4 when driving, then drop to 2 when idling yea? That's pretty much the rule of thumb and standard. Sometimes on a run, the pressures at just about 3 when driving, and drops to about 1.5 idle. Seems intermittent.
Checked the oil levels and its topped up to just below the full mark as it should be.
Trust the dial? Or something else going on?

Cheers guys! Appreciate your advice and opinions ... still learning my way around this wonderful but sometimes strange car [

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zcacogp · Nov 30, 2010

The (apparent) drop in temperature when you turn the lights off indicate an instrument (or wiring) fault. That sounds like a bad earth in the dashboard cluster somewhere, which may affect the oil pressure gauge as well.

Oil pressure is affected by a lot of things. I wouldn't worry about any one particular reading, but watch for a trend over time (increasing or decreasing.) The recommendation in the manual for my S2 is that if the oil pressure is over 1/2 bar then things are OK.

Oli.

Outrun944 · Nov 30, 2010

ORIGINAL: zcacogp
The (apparent) drop in temperature when you turn the lights off indicate an instrument (or wiring) fault. That sounds like a bad earth in the dashboard cluster somewhere, which may affect the oil pressure gauge as well.
Oil pressure is affected by a lot of things. I wouldn't worry about any one particular reading, but watch for a trend over time (increasing or decreasing.) The recommendation in the manual for my S2 is that if the oil pressure is over 1/2 bar then things are OK.
Oli.

Hi Oli, thanks for the reply.

That's interesting, I've had quite a lot of wiring problems - bad wiring was the cause of the pop-up lights staying up (http://www.porscheclubgbforum.com/tm.asp?m=575283) in the end. Talking of earths, the earth that connects to the rear O/S boot strut isn't err earthing as far as I can make out too for the rear defrosters (connecting a wire to a metal part in the boot it works fine). Possibly not at all connected, as you say - it's in the dash cluster though.
Is the earth in the dashboard cluster easy to get to? I've not worked it out from the wiring diagram I have yet.

Oil pressure, yea ... reading up on some other topics it seems a lot can cause strange readings. I would say, that after a drive of 30mins + the oil pressure gauge every time has changed from the 2/4 on startup to 1.5/3 eventually and stays that way - until cold and starting again.

It hasn't dropped below 1 yet (then I would be worried) but you know ... anything 'unusual' with these cars gets my attention and makes me worried/concerned. I try not to ignore what the car is telling me!

zcacogp · Nov 30, 2010

Al,

Earths on older cars often go bad. The ones on my S2 seem OK, but I have spent many an hour tracking them down and improving them on old Golfs.

If you aren't too fussed about a concourse job then the easiest way to improve bad earths is to dig into the harness, find the earth wire (almost always brown, but check the wiring diagram), splice into it and make a new earth somewhere else. That's often easier than finding the original earth, discovering it is rusty and nasty, taking it apart and cleaning it up and re-making it. Improving a bad earth can also cure a load of other, apparently unrelated problems as well and can be very satisfying.

Your dashboard problems are a classic sign of a bad earth. Turn the headlights (and dash lights) on, and the bulbs come on. That current meets a resistance at the bad earth, and hence the voltage of the earth wire goes up (i.e. is no longer at 0, as it should be.) Instruments which use this earth as a reference therefore start to read incorrectly.

Oil pressure - I know exactly what you mean, but I recall some wise advice from a more experienced chap when I fitted an oil pressure gauge to my old Mk1 Golf; "Oil pressure gauges are fitted by owners who worry about their cars too much, and then they have another thing to worry about." (I didn't take his advice and did fit such a gauge, and then spent a lot of time worrying about what it said ... ) [

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Oli.

Outrun944 · Dec 1, 2010

ORIGINAL: zcacogp
find the earth wire (almost always brown, but check the wiring diagram), splice into it and make a new earth somewhere else.

Cheers Oli! The defroster earth should be easy enough to do - the wire is sticking out the inside side panel of course! Ok just running it to an exposed metal part? Or a nut/bolt that comes through from the chassis?

Your dashboard problems are a classic sign of a bad earth. Turn the headlights (and dash lights) on, and the bulbs come on. That current meets a resistance at the bad earth, and hence the voltage of the earth wire goes up (i.e. is no longer at 0, as it should be.) Instruments which use this earth as a reference therefore start to read incorrectly.

Yep, that makes total sense.
If anyone can be of assistance in tracking where this earth wire is and going to that would be most appreciated

Oil pressure - I know exactly what you mean, but I recall some wise advice from a more experienced chap when I fitted an oil pressure gauge to my old Mk1 Golf; "Oil pressure gauges are fitted by owners who worry about their cars too much, and then they have another thing to worry about." (I didn't take his advice and did fit such a gauge, and then spent a lot of time worrying about what it said ... ) []

LOL! That's so true [

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This is the only car I've ever owner that's had an oil pressure gauge like this, so you know ... oil 'pressure' had never entered my mind ever before - just checked the levels were good. I guess that's all I need to do on the 944 ... but if we've got good levels and the pressure starts consistently going below 1 then we perhaps might know there's some other bad issues occurring. Perhaps then ... a good indicator of issues cropping up you wouldn't have noticed otherwise who knows

Cheers
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zcacogp · Dec 1, 2010

Al,

An earth is an earth - so anything that has good connection to bodywork. Bad earths in the dashboard I always solved by drilling a small hole in the steering column bracket and putting a self-tapping screw into it, then connecting the spliced wire to the self-tap screw. Any connection would work, but I'd avoid making connections to doors and bootlids as they may not be that well earthed themselves.

Oil pressure; yes, cause of much un-necessary concern. It's always worth keeping an eye on the gauge, but not too close an eye. If it drops suddenly, worry. Otherwise, don't. A number of things will affect the pressure; temperature (as it warms up the oil thins and pressure drops), oil type and driving type. If the pressure drops noticably over a period of time (several months or more) under similar conditions (i.e. same oil, same temperature, same driving style for the same period of time) then it may be worth looking into, but this is pretty unlikely to happen.

All the best with the car.

Oli.

ETA: Tracing earths; only way I think is to get access to the dashboard loom and untape it until you find the earth - which should be brown, but you need to check the wiring diagram. The wiring diagram will also tell you where it is earthed, should you need to know. Splicing a new earth connection into it will mean you don't need to be worrying about the old one tho'.

peanut · Dec 1, 2010

ORIGINAL: Outrun944

LOL - so what do I trust? Lights on or lights off? hehe! OR do I have fault electrics?

I would suggest that you clean and check all your main earthing points as it sounds like they may be at fault for intermittant problems like these.

The most important ones are GPl which is just under your hatch lock behind the carpet.
GPll and GPlll both of which should be on the passenger side under the bonnet just in front of the battery.
Also the earth strap from the back of the engine to bulkhead and lastly the earth point down in the pass headlamp well. ( IMPORTANT) make sure that you pull the relay or fuse (or both ) to the headlamp motors because if you accidently trigger them whilst your hand is down there ..........[&o]

oops looks like Oli has got there before me . Thats the trouble with this infernally miniscule text size on modern LCD screen settings grrrr

sdelasal · Dec 1, 2010

Nick - that's a useful summary- thanks.

PKR944 · Dec 14, 2010

Hi,
Not too sure how things are going with the temp gauge on your car now. I have an 83 944 and same thing the thermo fan was turning on at approx 3/4 on the gauge and then on sunday I had some trouble and found the fan was not starting up. I had someone check out the car and he found that the connection behind the fuse in the fuse panel was not connected properly and there was not enough power running to the fan and causing the issues. The fan is now starting up approx mid way between 1/2 and 3/4 now.

You might just want to keep this in mind.

Paul