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New 924S owner with speedometer, cooling system questions
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Thu Apr 26, 2018 7:40 am    Post subject: New 924S owner with speedometer, cooling system questions Reply with quote

Hi all.

Though I have been a member of other Porsche forums for something like 15-20 years now, it has always been for my '73 911T (the long hood forum).

In the last year, however, I have acquired an '88 924S, '86 928S, four (yes four) 944s (2 complete cars, 2 rolling donors, none running yet).

I've had the 924S for about 6-7 months now and am finally getting around to getting it sorted (so my son can drive it this summer).

It has two (2) issues requiring immediate attention:

1. The coolant temperature gauge runs very hot
2. The speedometer needle "bounces" a bunch above about 20mph (and the odometer doesn't work, though the trip meter does).

Regarding the cooling temp gauge reading hot/high, it appears to be functioning because when it was cold here in Austin, it would read at about 60-70% of max, when warm/hot here, it reads about 85-90% of max.

The seller (via BAT -- bring a trailer) told me that it was just a sensor ground issue, and I am taking him at his word (after all he gave me a very, very, very good -- dare I say screaming -- deal on a 928S with a bad 2nd gear synchro and non-working AC but otherwise sound car in a two-fer deal).

I am guessing that when it's cold, say below 30 degrees, the normal needle reading would be at 40% of max, not 60%, and 50-60% when the ambient temp is hot, so maybe it really is a calibration/ground issue?

How would one suggest I go about troubleshooting this to determine whether it really is a ground versus something else: bad sensor, thermostat, clogged radiator, etc.? I just got done sorting out all the electrical on an X1/9 I bought (it had priority as I was driving it targa-off during the cooler than usual winter/spring here in central Texas), so am pretty handy with a multimeter and wiring diagram right now (and the Fiat had lots of ground/resistance problems).

The issue with the speedo is more of an irritant. I am guessing that it is the speedo gauge itself and not the speed sensor because there is an issue not only with the speedometer needle not reading accurately/bouncing around -- sometimes it does it continuously, other times it settles down after driving it a while -- but also with the odometer, so my issue is with the whole speedo gauge in the instrument cluster.

Does everyone agree with this or could it be the speed sensor? (presumably, the speed sensor also drive the odometer and trip meter mechanisms as well?)

Can these be repaired or do I need a new cluster? Haven't taken it out yet, but Haynes says the cluster is a one-piece integrated unit.

If so, is the 944 cluster a plug-and-play as I have four of those and long-term will only need two? Or is there someone that fixes these clusters relatively cheaply?

Otherwise, I love the 924 -- always wanted one since I was a kid -- and look forward to driving it a bunch once I have these little irritants sorted out, especially since it has great R134 AC while the 911T doesn't and the 928 does but it doesn't work yet (too many projects).


Last edited by austinporsche on Thu Apr 26, 2018 3:00 pm; edited 1 time in total
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Thu Apr 26, 2018 1:33 pm    Post subject: Reply with quote

Welcome to the board.

What does the temp gauge indicate right before the radiator fans kick in?

The speedo is cable driven by the left front wheel grease cap. The speedo is a separate unit and can be removed from the cluster and be repaired or swapped out.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Thu Apr 26, 2018 2:59 pm    Post subject: Reply with quote

Thanks.

I have a Haynes 944 manual that indicated the speedo was sensor driven ,not mechanical, but I guess the 924S and 944 are not as alike as I thought.
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Eric P  



Joined: 21 Jun 2017
Posts: 169
Location: NY, USA

PostPosted: Fri Apr 27, 2018 1:57 am    Post subject: Reply with quote

It's my understanding that you shouldn't push the trip reset button while the car is moving as it will strip out the odometer gear. Replacement odometer gears are available on ebay if it bothers you enough to drop the coin on them.

The bouncing speedometer could just be dust/gunk in the mechanism. I've pulled a few mechanical speedometers apart (off from a motorcycle, but still the same concept). If you get gunk or corrosion on the little spinning magnet inside, it can make the speedometer bounce.

As far as the temp gauge goes, you really should flush the radiator and replace the coolant if it hasn't been done recently. When you do that, replace the thermal switch at the top left of the radiator. It may have the wrong switch in there. That's what tells the fan to turn on/off. Sometimes the switches stick open or closed too. They aren't expensive and it rules out that variable.

Seeing as you own a 928 and 944s, you've probably already thought about this, but when was the timing belt last done? The service interval is fairly short (~2 years or 30k miles). If it's been sitting since it was done last, just replacing the belt would be cheap insurance assuming the rollers and water pump feel good.
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1980 924 NA, US model
1987 924S, US model
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Fri Apr 27, 2018 6:27 am    Post subject: Reply with quote

Thanks for the reply.

Am going to tackle the speedo here in a week or two step-by-step.

1. Inspect hub end of cable
2. Inspect gauge end (somewhere I read that some 924 speedo cables go from the hub to an intermediate "counter" ss metal box under the dash that sets off an O2 service sensor light -- ever heard of that?)
3. Pop pone the speedo itself and renew it as needed

Regarding the temp gauge, here are some further observations:

Whenever the car is relatively cold and I turn on the pop-up lights, the needle pegs momentarily before returning to wherever it started

The cooling fan runs when the key is set to accessory but not when the key is turned all the way off; should the fan turn off when the car is turned off or should it continue running until the fan sensor tells it to turn off

The temperature gauge will peg at 100% in the red when stopped but then drop from 100% to about 80% once the car is moving, indicating to me at least that there is some heat exchange taking place; could this just be airflow around the motor or is the coolant system working (even if the sensor is not)

The coolant in the expansion tank, while hot, is not scaldingly so, and after driving the car for 20 minutes, the cap could be opened without coolant spewing all over the place.

I am guessing right now that the water pump is fine (no leaking of coolant, not a drop), and that if the thermostat was blocked/failed that there would still be some passive "backflow" from the engine to the radiator, which might be indicative of the slight cooling gain I get when the car is moving.

Any thoughts? I understand that the thermostat is somewhere behind the timing belt and is a real PITA to change -- is that right?
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Fri Apr 27, 2018 7:34 am    Post subject: Reply with quote

OK, did a little Haynes manual reading, and the thermostat is accessible from below (above?).

As the car has moved from Seattle to Texas, probably not a bad idea to put in a lower temp thermostat anyway.

Regarding the fan, it appears that it should run even if the key off if it is hot enough, so it looking like replacing the fan switch is on the plan as well.

I have been trying to locate the coolant temperature sensor but can't seem to find it; on most cars it is somewhere at the top of the engine.

Does the 924 have a fan temp switch and a temp sensor or does the fan temp switch serve both functions (sensing and switching). I got the impression that the fan switch was an on-off continuity thing and did not have variable resistance, which is what you would expect of a sensor.


Last edited by austinporsche on Fri Apr 27, 2018 10:53 pm; edited 1 time in total
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Harm  



Joined: 02 Apr 2009
Posts: 1308
Location: Holland

PostPosted: Fri Apr 27, 2018 8:51 pm    Post subject: Re: New 924S owner with speedometer, cooling system question Reply with quote

austinporsche wrote:
Hi all.

2. The speedometer needle "bounces" a bunch above about 20mph (and the odometer doesn't work, though the trip meter does).


Most of the time a bouncing Speedo needle tells you the speedo cable has a steep bend in it; Under the hood or behind the dashboard instruments cluster. Check if the previous owner placed the cable in an evenly curved line from the wheel hub onto the speedometer in the engine compartment. Smoothing the curve will help the lines "inner feather" to rotate evenly and won’t wind up and release stressfully, leading to the bouncing needle.
Easy fix, HTH
Kind regards,
Harm.
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Porsche 924 NA 1982 LY7A/A3A3 _ Greater driving pleasure never harmed anyone.
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Fri Apr 27, 2018 10:52 pm    Post subject: Reply with quote

Thanks, Harm.

I am diving into this car this weekend (finally -- owned for 6 months and haven't done much so far other thasn look under hood a couple of times) and will start with that on my bouncing needle checklist.
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Sat Apr 28, 2018 3:46 am    Post subject: Reply with quote

austinporsche wrote:

Does the 924 have a fan temp switch and a temp sensor or does the fan temp switch serve both functions (sensing and switching). I got the impression that the fan switch was an on-off continuity thing and did not have variable resistance, which is what you would expect of a sensor.


Yes it has both. The temp gauge sensor is located on the top of the block under the intake manifold.

The thermostat is built into the water pump inlet. Use something like this to determine your coolant temp:

https://www.walmart.com/ip/Loadstone-Studio-Non-Contact-Infrared-Thermometer-58-716-50-380-Temperature-Gun-Precision-Laser-Technology-Kitchen-Home-Industrial-WMLS2417/837893989?athcpid=837893989&athpgid=athenaItemPage&athcgid=null&athznid=PWVAV&athieid=v0&athstid=CS002&athguid=466001f5-589a1f29-d2f09a4ebd2f124a&athena=true
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977


Last edited by Paul on Sun Apr 29, 2018 12:25 pm; edited 2 times in total
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Daniel12  



Joined: 19 Apr 2018
Posts: 10
Location: South Carolina

PostPosted: Sat Apr 28, 2018 6:22 pm    Post subject: Reply with quote

Sorry these pics are so big, I don't know how to resize them.

austinporsche wrote:
Thanks.

I have a Haynes 944 manual that indicated the speedo was sensor driven ,not mechanical, but I guess the 924S and 944 are not as alike as I thought.


The late (85.5+) 944s have the new dash and integrated instrument cluster. That speedometer is driven by a sensor on the transaxle. The early 944s and 924S share the cable drive speedo with the 924s.

The picture below shows the cable exiting the firewall and going down through a locator bracket before turning toward the left front wheel.





Make sure the end of the cable protrudes fully through the grease cap on the hub. The end of the cable is chamfered and if not fully through the cap, can spin-catch, spin-catch and cause needle bounce.





The thermo switch for the fans is in the radiator on the driver's side below the radiator hose. The wires to it are indicated by the blue arrow. The green arrow points to a ground location on the front frame rail. Might not be related to your problem but make sure it is clean and tight.





This pic shows the "Temperature Transmitter" (red circle) and the "Temperature Sensor" (blue circle) in the block under the intake. IIRC, one is for the computer and one runs the gauge but I don't recall which does what.





Last, here is the factory coolant bleeding directions. I'm not sure if it's cool to post this photo so if it violates policy, please delete it.


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1979 924 Alpine White (in pieces) owned since '82
1987 924S Red ITS #12
1995 993 Polar Silver
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Sun Apr 29, 2018 3:59 am    Post subject: Reply with quote

Thanks.

Regarding the temp sensors, according to what I could figure out, the two are:

Blue one is the DME temp sensor (per Clarks garage, it is supposed to read 3000ohm at 40degF and around 220ohm a 212degF, which this one does); it senses off the coolant.

The one behind it is the coolant temp sensor. It looks like yours in the picture is the same single blade type on my 924.

Can you confirm that your back sensor is in fact single blade/pole?

Is that the correct sensor?

If so, any idea where I can get one as all I can find are the 2 blade types (like the blue one).
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Sun Apr 29, 2018 4:33 am    Post subject: Reply with quote

And that intake hose between what I am guessing might be the MAF and the throttle body really gets in the way.

It has a metal tube sticking into that air intake hose that is all that is keeping it in the way once the two hose clamps are removed.

I noticed that yours is removed in the picture.

Does that tube just slide in-and-out of the MAF-to-throttle body hose or is it glued or vulcanized in there?

I would post a picture but can't figure out how . . .

When I click the Img button, all I get is:

[img][/img]
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Sun Apr 29, 2018 10:43 am    Post subject: Reply with quote

Temp gauge sensor has a single pole: 944 606 201 00 Temperature sensor

Download the parts catalog here:

https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/

See page 46
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Sun Apr 29, 2018 12:29 pm    Post subject: Reply with quote

Here's a great article:

https://newhillgarage.com/2018/02/04/porsche-944-coolant-system-explained/
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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austinporsche  



Joined: 26 Apr 2018
Posts: 13
Location: Austin, TX

PostPosted: Sun Apr 29, 2018 12:59 pm    Post subject: Reply with quote

So the temp gauge sensor is single pole and is only available directly from Porsche then?

Last time I ever bought anything from genuine Porsche were two rear torsion bar end caps/retainers for my 73 911 from the parts department at the Austin dealer -- it was maybe 2009 and they only cost about $12 each as I recall.

That said I am not shedding any tears for Roger Beasley Porsche: the guy must make a fortune as you can't pull up to a stoplight anywhere in Austin and not see some brand new 911 variant along with all the pickups.

I am guessing that prices have gone up a bit since the days of the $12 torsion bar end cap
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