SalzundPfeffer

I'm struggling to understand how the fan could run at slow speed on an early car due to the fact the temp switch is a single element, if I'm reading the diagram correctly.



Once the ignition is turned on and the cooling fan relay is energized, the resistor used to run the fan at slow speed when the car, is off is by-passed.

The bouncing with the temp gauge only happens once the car gets warmed up and it only bounces between two tick marks. I presume a bad ground would cause the gauge to bounce all the time. Although as the temp changes, so does the voltage so I suppose its possible for the gauge to behave differently at higher temps. Can anyone confirm this?

originalmotorhead

My 84 just started doing this today, like an hour ago driving into work.

Up till then, the needle had been fixated at the 12 oclock position(middle tic mark), once warmed up, but today driving to work it was at the third tic mark over(97 on the chart).

And it too would rise a little, then drop, then flip back. but it was not consistantly doing that. Needle would only do that every so often.(inconsistant but definatly more so when the needle approached the upper area of the gauge.

I've got 20 miles of freeway commute and 4 miles of downtown traffic and even on the freeway it was on the 3rd tic. It's about 50 degrees and rainy this morning, conditions that should not warrant hot operation.

Really got me worried when it started climbing this morning.

I'm planning to pull the lower rad hose this weekend and inspect the thermostat.

Just hoping I can make it home ok with the car. WHen I got to work, I let it idle for a bit and temp stabilized at third tic but didn't seem to want to go lower.

Tom

originalmotorhead

Wanted to throw in 2 cents on something I have seen before.

Sometimes when the head gasket starts to go, you can get an abruptive temp fluctuation under power, however, if that is the case, you typically get some coolant loss from the resivor.

Tom

SalzundPfeffer

Thanks for your input. Please follow-up on your findings when you take a look at the thermostat. That is my leading theory at this point followed by a clog and bad grounds.

I have about the same commute as you. ~10 minutes of freeway and ~5 minutes stop and go. I am continuing to drive it now that we are below freezing during my commutes. I have not noticed any coolant loss at this point. Keeping my fingers crossed.

Just need to find time to tear into the 944...You see, my other car is a piece of **** too...I've been wrenching on on my '93 jeep the past few weekends, getting it ready for winter. But, I wouldn't have at any other way. I somehow find joy in maintaining a fleet of vehicles with an average age of 22 years old

smokin_944

On an early car, There is only one resistor and it is in play until the temp reaches the high temp point. Once it reaches that point, it is bypassed and both fans run at high speed. Read what Clark's says.

On early 944s equipped with air conditioning, there are two electric cooling fans. The driver's side cooling fan is supplied via a parallel circuit. One leg of the parallel circuit has a resistor which causes the fan to run in slow speed. The other leg of the parallel circuit consists of a contact in the cooling fan relay. The passenger's side fan is supplied via a contact in the cooling fan relay.

When the coolant temperature reaches a preset value (normally 92 °C or 198 °F), the temperature switch (normally referred to as the thermofan switch) closes and cause the driver's side fan to run. We'll refer to it as the primary fan. Since the resistor in series with the fan is still in the circuit at this point, the fan runs in slow speed. The fan will run as long the temperature remains above the setpoint, regardless of whether the ignition is turned on. This is a common problem area which will be discussed later.

When the ignition is on and the air conditioning is turned on, the air conditioning relay picks up. This causes the cooling fan relay to energize, closing two contacts. One contact causes the secondary cooling fan to run. The other is a contact that is in parallel with the "slow speed" resistor for the primary fan motor. This shorts out the resistor and causes the primary fan to run in fast speed. The second fan has no "slow speed" resistor so when it starts, it always runs in fast speed. Also, when the air conditioning is turned on (with the ignition on), the primary fan will run regardless of coolant temperature.

When the ignition is turned on, if a high temperature condition is sensed by the thermofan switch, a contact closes in the thermofan switch circuit which energizes the cooling fan relay and causes both fans to run in fast speed.

originalmotorhead

That's exactly what i see on my car.

Tom

SalzundPfeffer

Can anyone confirm on their early 944 that the driver's side fan operates at slow speed with the car on? I just don't see how it can without a dual element fan switch like the later cars.

Here is my reasoning.

The slow speed operation of the driver's side fan is governed by the resistor, which is in parallel with the cooling fan relay. When the car is off, it's a no-brainer; with no power to the cooling fan relay power has to flow through the resistor causing the driver's side fan to run at slow speed.

However, when the car is turned on (which is the same thing as saying the cooling fan relay is energized), if the thermofan switch trips, it closes both contacts in the relay allowing power to flow to both the driver's and passenger side fans. Since the resistor is in parallel with the contact in the relay, power will take the path of least resistance (shorting around the resistor).

There would have to be another component (a second element in the thermofan switch) in order for the driver's side fan to run slow while the car is running.

I know what Clark's says, but the second paragraph is not clear since he doesn't indicated if the car is on or off. The last paragraph tells us what happens during a high temperature condition when the car is on, so this leads me to believe the second paragraph refers to when the car is turned off.

Just my take. The only reason I'm beating a dead horse is that if the fan should be running at slow speed when the car is on, it could explain my temperature rise.

Thanks,
-bp

944Ross

BP, when I had an Early car, I had problems with my Temp gauge, not exactly like yours tho. The problem turned out to be in the Tach! If you look at the FSM section on the stupid Upshift light, its circuits use temp gauge output as an input (upshift light doesn't work until engine is warm), and a problem in the tach can cause problems with the temp gauge (and vice versa). Everything OK in your tach?

SalzundPfeffer

Tach seems fine as well as the shift light. If I get in there to clean grounds I will take a look at that too.

originalmotorhead

Not to hyjack the thread but I think we both have about the same issue here and can share the troubleshooting.

Last night I did a little tinkering right after my commute home from work.

1. unclipped the single wire from the temp sensor(one that runs the temp gauge in the dash). Hooked up a potentiometer and turned back and fourth and verified gauge follows with resistance varriance.

2. Cleaned the connector and the contact button on the temp sensor. There was some green on both. One thing I noticed(and somerthing I suspect is culprit for jumpy needle) is that the button on my temp sensor rotates/little loose. I'm thinking my temp sending unit is faulty or intermittant because the button on the end seems loose. No leaks from it though.

3. Dab of grease on the end of the temp sensor to prevent future corrosion and reinstalled the temp gauge lead wire.

4. With car warm/hot/up to temp (from my 24 mile commute home), I opened bleeder screw and woosh fluid comes out but no air really. Thus, I think the sys is not cavitating/air bound.

5. Revved the motor(almost excessivly) while watching the coolant resivor. No bubbles, no fluctuation in coolant level. This kinda lends me to believe the head gasket is fine or least does not have a major leak. Have seen before where head gasket failure from combustion to water jacket will cause lots of bubbles in coolant or fluid to rise rapidly in resivor.(didn't see that here)

6. Looked over all fuses. All were good. removed and reinstalled fuses for the fans.

7. Verified only the drivers side fan is working(it works on both low and high speeds<low when car is off, high when ac **** is on or sending unit wires jumpered or when car temp gets up there>). The pass side fan does not come on at all, regardless of what I do with the sending unit wires on the radiator or the ac controls. I did verify the fan is good by hooking it up directly to the battery.

8. On the commute home, I tried to drive the **** out of the car on the highway to see if that caused variance in temp needle. The car is an automatic, so I would just tromp it while on the freeway and hold it to the floor for a few seconds or so. There was no real variation in temp, if any. This is again making me think no head gasket issues. People have told me they have seen temps rise on the back streight at the race track when the head gasket is going.

9. Looked at oil filler cap(yellow cap) for any condensation. Not a drop, dry as can be. I had cleaned it completely a week ago while doing oil change. Oil level was also unchanged / at level. This makes me think no issues with head gasket issue.(least not from the coolant jacket to oil passageways)

10. Tightened/inspected/etc the grounds on the back of the motor, front by the headlights(cause easy to get to). I broke em loose, shot with pb blaster(great at eating corrosion off), and retightened.


Last night, after all this tinkering, I took it for a test drive(test drive was about 2 - 3 hrs after I parked it. Car was cool enough to pop the rad cap by then)

Needle did jump once, within first two minutes, then no more flicker. Car went from colt to hot within a few miles. Temp stuck at the middle tic mark pretty much the whole time. It did move little to the right here and there but not by much. Grantted, temp had dropped significantly and i had to run the heat. I think the cleaning of the contact helped the needle flicker, however, i still suspect the sending unit is on the fritz because the button on the end would rotate/was loose.




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Items that I did not get to do last night, but plan to do this weekend / over the holiday.
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A.
Figure out which relay is the fan relay and remove/inspect/reinstall or possibly replace(Need a part #). Maybe go so far as to jumper it for testing purposes.

B.
Drain cooling sys into clean container to inspect for any debris, oil, or discolored crap. (because I had just flushed the system a week ago)

C.
Yank lower rad hose and look at the thermostat. Check the temp markings on the t stat, possibly replace(if I can get a new one at autozone). I am tempted to remove the t stat completely, and refill system and drive to see what, if any, difference in behavior I have. No flames, I realize this is not preferred as it takes longer for car to warm up but if I don't have a new or known good t stat, I want to rule ot the t stat is issue.

D.
pull front timing belt cover and ensure there is proper tension on the timing belt and on the water pump. I had replaced the belts a week or two ago, so this is more or less a sanity check. Thought behind this is if there was a little insufficient tension, pump may be slipping and thus not consistant coolant motion from the pump. I am kinda doubting this because when I ran the crap out of the car on the highway, the temp was pretty well unchanged.


Bottom line, I need to get that second(pass side) fan to work automatically. I also am thinking the car is not getting as hot as the gauge says, that most of the problem is likely the sending unit. When I park the car, the rad hoses are not insaingly hot, resivor tank is not melting. The rapid warm up leads me to think the thermostat is stuck closed or it is not opening all the way.

Will post more when i test more. And if I decide to put the car off a cliff, I'll youtube it for ya'll !

Tom

smokin_944

This is where your problem lies. The early car DOES NOT HAVE A DUAL ELEMENT FAN SWITCH LIKE LATER CARS. (I am guessing you mean a thermal fan switch, the one that screws into the rad) All early cars that are wired stock operate the way Clark's describes. The driver's side fan runs at slow speed with the car running when the setting of the thermal fan switch is reached.

Tom, your problem with the second fan is relay related. The second fan should come on when/if the high temp condition occurs. Furthermore, if the gauge is accurate and you are at the second tic mark while cruising, the car is running at approximately 89*C which is OK in anyone's book.

originalmotorhead

I found a relay layout.....


http://www.network54.com/Forum/42613...fication+chart

Tom

SalzundPfeffer

I think this answers my question about early driver's side fan operation. When the single element switch is tripped the fan will operate at slow speed when the car is off and at high speed with the other fan when the car is on.

Tom: My second fan stopped working last summer and I spent an entire evening trying to figure out where the fault was. I checked the fuses first (visually everything looked good) but I still couldn't figure out why power was not getting to the fan. I revisited the fuses later and did a closer inspection on Fuse #5. While the filament section was OK I noticed a hair-line crack on the end of the fuse. This was breaking the circuit and not allowing power through. Replaced the fuse and I was good to go. Also check the operation of your fan relay too.

I bled my system too and didn't noticed much air.

Now that temps have really dropped here, my needle is settling in at the middle tick. If I had a head gasket leak I presume that the lion share of the heat coming into the water jacket would be unaffected by ambient temperature. So again, I don't think my gasket is going.

I need to check for condensation in the oil reservoir and double check my grounds.

Since I will be parking the car once the snow starts flying I may just do a complete service on the cooling system. New thermostat, fan switch, temp sensor and take the rad to a shop for a flush. I hope there are a few more warmer days left to do this before it really gets cold.

originalmotorhead

I'm waiting for the parts place here local to call me back about a new (and lower temp) t-stat for my car. they are having it delivered over from the wharehouse or where ever. 944 106 129 05 is the part # and it's a 80celcius t-stat vs the 83c that early cars came with early cars. Apparently its reccomeneded to go to the cooler one(the cooler ones came in the s and s2 cars ??).

also, i found two part #'s for the sending unit for the temp gauge, not sure exactly which one is correct.
047 919 501 A
928 606 201 01
i suspect the 928 is the proper part but....

If I can get the t-stat later today, tomorrow i'll start on the project before i gorge myself with food. Will def check out that #5 fuse for cracks too! (or i will just replace it)

Tom

CorsePerVita

The only thing I can recommend is first off to ensure beyond a shadow of a doubt that you do NOT have a gasket leak. Do a compression test and/or leakdown to ensure all is well in the world. It doesn't sound like you do, but it's usually the elephant in the room that no one ever addresses because they hate doing them. Even if you don't, it's at least peace of mind.

If you bleed the system and it is bled correctly there shouldn't be any air instead of "not much air". Air in the system will/can cause sporadic operation and it will act funny.

The other thing I was going to suggest would be the type of thermostat you installed. If it is not an OEM stat and it is an aftermarket stat, many of the aftermarket stats (like the napa or auto zone stats) have a much SMALLER opening than the OEM stat. Reason I bring this up is I had issues with my car getting hot and it would run at the 3rd mark (1 mark before red zone). This was after I replaced the thermostat. It would sometimes go down to 1/2 on a VERY cold day but most the time it just hung out at the 3rd line. That is pretty hot.

I went back to an OEM stat at the normal temperature and it has hung out at the 1/2 mark all the time, every day, 7 days a week, 24/7 and goes above it on rare occassion and the fans kick in and then it's back to normal.

Once the thermoswitch kicks in your driver side fan should turn on and the temp would lower.

Have you tried turning the A/C on? It should technically kick the fans into full blast, once they do that, does it cool down any? Does it change it? If it does then it's fan operation. If not you have something else going on.

My issue with my main heating problems ended up being crapped out stat and a partially clogged radiator.

All the basics to check...

- Does the lower radiator hose feel hot once the temp goes up a little? If not the stat isn't opening, or not opening much. If it is hot then the stat is opening.

- Is the radiator cool in spots? If it is operating correctly after the thermostat opens you should be able to turn the car off and feel the radiator, it should be WARM to the touch. If it is evenly flowing it will be warm. If it is blocked or partially clogged it will be COLD to the touch in other areas. Mine was partially clogged on the bottom thanks to the PO using radiator stop-work. I mean stop leak.

- Water pumps usually sound pretty horrendous when they go out, so unless it sounds like wailing death I would check the basics first.

- Have you taken the thermostat OUT of the car and tested it? I usually will get a tester for steaks (they cost a few bucks and will read the temp perfectly for ya!) and heat up some water until it is the same degree that is required for my stat to open. Then put the stat in and watch it open. If it opens PART of the way you've got a sticking stat that isn't giving enough flow. If it refuses to open, heat the water up a bit more and check the temperature and try it again, if it absolutely refuses to open it's sticking closed, or it may open when it gets REALLY hot and that can cause issues too.

- Other thing is bubbles in the system. Once the system is bled it SHOULD NO LONGER HAVE BUBBLES IN IT. If you are able to bleed the system and bubbles keep appearing you may have something like a blown HG. Even little ones add up over time.

- If you do get the rad flushed then make sure you get it pressure tested while you are there for any pinhole leaks.