924 temp gauge problem
 

I have a 77 1/2 924 and the temp gauge flutters when at idle. It also seems to run about 1 notch hotter than normal on the gauge. I recently replaced the engine and it ran fine for 3 months and a couple weeks ago it started running a little hot. I've check/cleaned all the grounds and elect connections everywhere and burped the coolant but the problem is still there, any ideas?

Michael

Faulty radiator fan switch maybe?

I think it's bad too. If I disconnect the two wires and touch them, the fans should come on, right? Right now, after I shut off the engine, the fans don't stay on unless I turn back on the ignition. Would that make me run hotter and temp gauge flutter? thanks for the response.

If you jump the rad fan switch, a fan should run on low with ignition off, high with ignition on. Since yours don't run with ignition off, that indicates that your rad fan resistor (which supplies power at all times) is shot; this is common, since on the early cars it's located at the top of the radiator - a rectangular box-like ceramic thing. It's probably corroded to pieces, since water runs down the hood right onto it. Lousy design. Porsche fixed it for later years by relocating it to the inside firewall, behind the tach.

But I wouldn't worry TOO much about that, since the fans will apparently work with key on - that's by far the more important condition!! However neither answers whether or not your temp switch, in the rad, works. You need to get the switch hot and see if it turns on; either by seeing if the fans turn on when then engine is hot, or boil it in a pot of water and measure it with a multimeter. Or just replace it anyway.

The temp gauge itself should not flutter. Water temps do not move that quickly. You have a wiring problem. If your grounds are good (glad to hear you started there - you're paying attention!) then you likely have a bad wire to the sender (assuming the sender isn't bad).

Do you know where the sender is located? It's hard to see, but it's at the back of the head by the hoses that go to the heater core. If you remove the wire from it and touch it to ground, the temp gauge should peg as I recall. Most likely, it's the wire between the gauge and sender; these wires in the engine wiring harness often get cracked and corroded over the years, and may need to be replaced.

Hey Vaughan thanks for the suggestions, I replaced the ground for the temp gauge and flushed the rad and put in the orange stuff. The needle didn't jump around anymore and never got above halfway on the gauge. Sweet!!
Ok now another one... my windshield wipers like to make a ghost pass for one pass for some reason. Usually when I make a turn and the turn signal clicks back off. Sometimes they just go on for one pass for no reason. Any ideas? I know it is an electrical issue (again), but where to start?

Excellent!

The ghost wiper mode is usually caused by a bad grounding of the steering column; you can add a ground underneath, like just behind the lock mechanism, usually fixes it.

I noticed that the grounding harness behind the firewall still has one open male end that's not being used. I suppose I could connect one to it. Where on the steering column would I attach the other end?

There may be an open bolt by the lock - just go underneath, see what you see.

cool thanks, I'll try it tonight.

Well, I think I'm back to square 1 again. I went for a drive yesterday and the gauge started bouncing again and the temp went up again 1 notch away from the red. Is there another ground that I can add somewhere else or am I overlooking something? I plan on getting a thermometer today and checking the actual fluid temp. What should normal operating temp be and should I check it in the expansion tank or maybe inside the bleeder plug? This is getting very frustrating!!

1 notch away from red isn't horrendous; do the fans come on at that point, and what were the driving conditions? As I mentioned, when you're driving at speed (like on the freeway) and come to a stop (traffic jam like I hit every day on the way home or an exit ramp and down to city speeds), the temp will spike up that high before the fans come on - they usually come on at the 3/4 mark - and bring it back down.

When cruising at highway speed, the temp should be reading at the first (1/4) or second (1/2) mark depending on t-stat selection.

It's also possible that you may need to bleed it again... might have uncovered a spot of air in the system.

...and look on the bright side; while it may be frustrating to isolate the problem, it isn't really costing much of anything in parts, and aren't you glad you're not paying a Porsche tech through the nose to spend the same amount of time and not really fix the problem?

yea I sure am glad to not be paying a Porsche tech to do the same things I'm doing!! I did buy a thermometer and checked the temp. When on the highway, the gauge reads just under 3/4 and I pulled over to check the temp, it read about 175 degrees. I checked the rad expansion tank and also inside the bleeder plug. I also just bled the system again (just for fun) and it seems like I got all the air out. So why is the freggin thing still reading hot? The old engine would not get above halfway but this one can't seem to stay under. AAGGHHH!!!

:)

That does seem like a high reading for the temp - I can't say I've ever cross-checked with a thermometer, though. So back to the possibility of either the gauge reading high, or the sender perhaps being incorrect?

I'll have to take another look at the wiring... wonder if maybe the gauge isn't getting a proper full battery voltage? Any chance you can pop the thing out, check that? Have you a multimeter?

yea I have one. I can disconnect the connection at the rear of the gauge with no problem. Do you know how much juice should be going to the gauge? I think I may just run a whole new ground directly from the sender to the gauge and not go thru the main wiring harness, maybe that'll work. If not, I have the old sender from the old engine that I know works fine, it just really sucks trying to get to it. Do you know what normal temp should be?

Michael
I've owned 3 -924"s. And each time something was wrong with the cooling system.
Things I learned.. Check the system pressure with a radiator pressure gauge. If any problems it could be a leaking, broken radiator or the hoses may have a very small leak, so small that it stops when you shut off the engine.

Also, it takes maybe a good half hour to bleed your system, properly. Its not bled until all bubbles are out (under hot engine conditions).. Have patience..

Make sure that your heater system is on (open for the fluids to go through) when you bleed the system. This is something that is missed, constantly.

If the thermostat is bad, your car will get very hot.

Anyway, over heating problems are not always electrical in nature.

Gordon

Sure, but his measurements, to me, don't seem to indicate temps that should read that high on the gauge. We did also talk offline and went through the whole bleeding procedure, which did (along with a flush) seem to help. Now it's just a question of the gauge function.

Sure, it would not be a bad idea at all to run a separate ground - even just for the purposes of testing.

OK, looking at the diagram, unless I've got the wrong one, the only ground for that gauge is through the sender - blue with yellow stripe wire. Power is a common feed from the 15 terminal of the ignition switch, shared with the rest of the gauges and warning lights. There really just isn't much to the circuit.

Given the changes made (since it last registered properly), about the only options here are either the problem's electrical, in which case yes, the sender is most suspect (as the only new component), or the engine really is running warm, in which case you either need to bleed it again, or maybe it's running too lean or improper advance? Check to make sure the vacuum advance line to the distributor is still clear - I've seen them melt shut and pop motors. First sign is the engine runs hot.

Again, when it got to the 3/4 mark, did the fans come on?

i think the fans have been coming on just over the halfway mark. So they see to operate ok. I'll try to bleed the system again and see if I can get any more bubbles out. Just to clarify my process.... Make sure heater valve is open, run car with rad cap off, fill expansion tank and keep filling until fluid comes out the bleeder plug. Am I forgetting something? That's how I've done it before, I guess I didn't have the patience that Gordon suggested and maybe didn't take enough time. Let me know any more thoughts, I really appreciate you guy's help here!!

Michael

Well, you do need to have it fully warmed-up...

Having the fans come on at the halfway mark, sound like you have the cooler fan switch (not a bad thing), but also gives some support to the idea that the temp gauge may actually be reading accurately. Back to bleeding and flushing.

Other stupid things to compare - does it only overheat at speed, and not while parked/idling? Some owners have reported about a cardboard flap in front/above of the radiator - designed to help duct air and make the radiator for efficient for this "bottom-breather" setup - that sometimes gets waterlogged, etc, and falls down in front of the rad, blocking it off. Take a peek, make sure you don't have one.

Do you have the plastic front grille?

Did you ever replace or pressure test the expansion tank cap, as discussed?

I plan on getting a new expansion cap today, I've had a feeling that it may be leaking pressure. It's pretty cheap so I'll try it out. I'll look for the cardboard flap by the radiator and see if I have one. I've never seen one before but that doesn't mean it may not be there. Is it something that is easily seen? Back to your overheating question, yes, it only everheats while at speed, seems to go down when at idle. Then the gauge starts to flutter until I tap on the gas for a second. I don't think I have a plastic grill other than the plastic frame that is on front of the radiator. I think it just for looks though. It's under the bumper. I'll try the new pressure cap and see how it goes. As far as me bleeding the system again, Gordon said it should take around 30 mins to do, any other tips you can tell me about to make this easier? I'll be headed home around 10 am today to get started, maybe you can call me if you get a minute. Thanks!!! 317.339-3039

Michael

Another thing to consider might be is it running off in mixture... we talked about vacuum leak possibilities, which could cause it to run lean... also conceivable that the mixture setting is just off. This would be more consistent with a car that runs hotter at speed than at idle - since then it's under load.

Go replace all those old vacuum hoses, but also take a peek at the plugs - that should show pretty easily if it's running lean. Look at the #3 and 4 - those always run hottest/leanest.

Well I reset the timing and it's good now, it seems to be a bit more peppy. I have the vacumn hoses ordered and will replace them when they come in. When I'm looking at the #3 and #4 plugs to see if they're running lean, what signs am I looking for? I took off that cardboard piece from in front of the rad and it does seem to stay right around 1/2 on the gauge if I stay in town. As soon as I get on the highway it starts rising slowly between 3/4 and hot. Then when I get back on city roads, it goes back to around the half mark, which is still too high. You said something about the mixture maybe being off, how do I check it or correct it?

The easiest way for you to check the mixture, assuming you don't have access to a tailpipe sniffer, is to read the plugs. Maybe someone can provide links to pics (or find 'em on Google), but basically the plugs should be caramel colored. If they're dark to black, you are running rich; if tending to white, you're lean.

To adjust, you need a long-T-handled 3mm allen wrench, fits in the hole in the top of the air flow meter between the fuel distributor and rubber boot. Unscrew to lean, screw in (clockwise) to richen. Move by very small amounts - 5 deg, really. When tuning the racecar, we'll typically dial it in in increments of 2 degrees.

There is another way to baseline, but let's see what your plugs look like first.

Ok I'll try it this weekend. But how do I tell when I have the right mixture, will I hear a difference in the engine? And if the mixture is off, are they typically off by much, because turning the screw 5 deg isn't a whole lot. I just don't want to make it worse. I have also ordered a new temp sensor just to be safe, the one on it now came with the rebuilt engine. Oh, by the way, I replaced the entire ground wire from the sensor and the gauge still bounces at idle :(

Correct, it is a very sensitive adjustment - that's why it would be helpful to know what your plugs look like, since you have no prior experience setting the mixture.

Michael,
From reading the many posts you have gotten, I can see that everyone has an opinion (and thats ok) However, you may get confused so please try an area, one at a time (your choice) such as tuning or system pressure or... But remain in one area and rule out all tests in that area before going to another. When you get finished, please let us know of the solution.
Gordon

Not sure what the latest on this is... it may be appropriate to try swapping out the t-stat... was that new with the new engine, or no? Some have run into problems with replacements...

Didn't get much done this weekend, too many Labatts on the lake. I did put a new t-stat in last week. I went with a 82 deg one. Probably won't get to play again til Wed, Buffett comes here tomorrow! I'm hoping the new vac lines and temp sender comes in today, will keep you posted. How will I tell if I have the mixture correct? Should I clean/replace the plugs and check them in a few days after driving or is there a way to check right after I adjust the mixture? Thanks for all the help guys!

That's cool - it's important to take a break every now and then!

You'll need to drive the car a bit, get the plugs up to temp, before you can see the results of mixture adjustment. Other than that, it takes practice - I do it by ear, often, just the way the car revs up.

That's cool - it's important to take a break every now and then!

You'll need to drive the car a bit, get the plugs up to temp, before you can see the results of mixture adjustment. Other than that, it takes practice - I do it by ear, often, just the way the car revs up.

Well I switched out the temp sensor and the temp now doesn't go above 1/2, even after driving for a hour on the highway. It's the one from my old engine but I still plan on replacing it with a brand new one when it comes in. At least now I'm seeing some results!! My new vac lines came in and I'll replace them tomorrow along with the ceramic balaster thing on top of the radiator, then my fan will work after I shut off the engine. Thanks for all the help but I gotta go get my 5 gal of margaritas mixed up, Buffett is today!! I'll check back in when I get the rest of the stuff switched out.

<groan> Well, somebody must've gotten the sensor out of synch with the gauge...

Good to hear - I don't blame you for taking a break after fighting through all that!

Hey Vaughn and Gordon-
Thanks for all the help, I just replaced the temp sender this morning with a brand new one and the temp hasn't even gotten above 1/4 on the gauge! And it doesn't bounce anymore either!! It seems to be running very good but I'm still going to replace all the vacumn lines today and see how that affects everything. Thanks again for all your help, you guys got me back on the road again, confidently! Well, until something else breaks....