CyCloNe!

I guys I've had this issue ever since I bought the car and I'm wondering if its my low speed fans don't engage correctly or gauge is incorrect. I constantly run at the top white mark, never over heats, high speed fans will engage and work. I have a new water pump, thermostat within the past 1.5yrs and stayed the same before and after the install. The coolant system has been bled many times. No loss of coolant or mixing with oil. Any ideas? When do the low speed fans engage?

milodorr

Just to clarify the symptoms, and the concern about the low speed fans, is the gauge at the top white mark even on the highway?

CyCloNe!

I usually dont drive on the highway, mainly back roads at 35mph, so i cant remember for sure. I know driving it usually it stays the same and if i remember correctly i drove it to church with the wife and it stayed the same on the interstate. I know the wires near the gauge temp sensor are a little damaged and wondered if that could be messing with it

944meister

I would try fix the wires to make sure, because if not, it sounds like your radiator is not cooling efficiently. I had a similar problem with my old n/a, bled the coolant in that sucker more than I needed to and the fans worked right, but still got hot. I changed out the radiator and the overheating problem was solved. You may want to try flushing the radiator first before buying a new one if it ends up that way, its much cheaper.

Lizard944

Possible options: Timing belt too loose and not spinning water pump properly. Faulty thermostat. Yes even a brand new Genuine T-stat can be faulty and open too late. I had a new one that I stove-tested before installing. It wouldn't open till it reached over 200F (normal ~180F) I installed it anyway and, sure enough, it ran in the upper 2/3rd range. Other less likely: Timing a bit off or running too lean. Also, some obstruction (scale) in the radiator. That's about all I can think of right now. The highway test might be helpful since you will have adequate airflow without the need for the cooling fans to engage. If it is still hot at highway speed then there is some circulation problem going on.

milodorr

Seems like we need *at least* one more piece of data to diagnose this.

To answer your initial question about about when the fans turn on: As controlled by the switch mounted in the radiator, according to the workshop manual for an '86 USA 951, the low speed fans turn on at 92C and the high speed at 102C. The A/C temp switch is also able to turn on the high speed fans (hopefully we can remove that complication here by leaving the A/C off). If an aftermarket switch has been installed, you're on your own. The switching temps might be engraved on the switch somewhere, as they are on at least some of the stock switches.

The three white lines on the gauge (low, middle and high) correspond to 80C, 90C and 100C, respectively. Perhaps you can use that information together with hearing when the fans operate to help you determine if your gauge is lying to you (assuming the switch in the radiator is working as advertized, of course). I battled a similar issue on my '86 turbo, and eventually fixed it by just cleaning the spade terminal on the gauge sensor. The fact that you have some damage to the wire leading to the gauge sensor makes me even more suspicious that this is the problem, but again we need a bit more data.

Diagosing this problem would be quicker it you had some independent means of measuring temperatures at various places in the system. If you don't have or want to buy an infrared thermometer, maybe you could borrow one from somebody.

michael2e

Sorted similar problem recently. Figure out when the cooling fans come on - in your case sounds like very late towards the upper white line on the temp gauge ( which is 100C) or higher ( like mine did). There are different calibrations for coolant temp switches and the one I had was 92C/105C which means the fans dont kick on until the coolant temp hits 92 and then at full speed if it gets to 105. I replaced mine with an 85C/XX which allows the fans to come on sooner and keep the engine temps in the normal range between 80C (lower white line) and 100C. Living in Florida it was necessary otherwise the car would run the higher temps all the time under load or in traffic. On the highway there wasnt any problem with cooling with the better airflow across the radiator or with the A/C on ( which turns the fans on by default)

You also should figure out what thermostat you have in the water pump. They also come in different calibrations. I had a 85C tstat originally when I got the car( which was a northern car) which meant the coolant flow was not circulating through the radiator until about mid way between the white lines on the temp gauge. You can get an idea when the tstat opens if you grab hold of the large hose coming from the water pump to the radiator. As the engine heats up it will stay cool to the touch until abruptly getting hot which indicates the tstat just opened Check your temp gauge at that point to get a temp reading. This all assumes your gauge is working normally. I changed my tstat for an 80C and now my car temps runs right around the first white line nearly all the time. I would put in a 75C tstat if I were to do it again since it doesnt get cold enough here to worry about warming up the engine. Good luck
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CyCloNe!

The water pump and T-stat are the updated versions. The radiator fan switch, which screws into the radiator, is new I replaced it after the old one failed and the fans wouldn't shut off. Thanks for the info gentlemen, I will do a little more digging and present my findings.

CyCloNe!

Well drove the car today, low speed fans don't engage, high speed fans do once it gets right past high white mark. The wires that were damaged on a sensor are actually the knock sensor, not the temp sensor. Driving the car at around 45mph the gauge will drop to half way between the top 2 white marks but then sometimes it will still be close to the top white mark while driving. I also noticed that when I drive I night if I turn of my lights my gauge reads lower, if I turn them back on it jumps up about 10-15f degrees.

CyCloNe!

Well I did this test and it looks like the fan relay is bad, fans would engage when terminals were jumped which would mean there's power to the fuse box (relay) and the resistors are working. So I need a new fan relay for my low speeds to work.

1. In the Bosch world, a terminal designation of “30” means it is un-switched battery voltage. Check for voltage at positions 30 M1 and 30 M2. You should get 12v + at both positions. If no voltage, check the fuses first. If the fuses are good and you have no voltage, then you need to check the wiring from the battery, the connections to the fuse panel, and the fuse panel itself. This is a little more involved and I will not get into it here.

2. Check for continuity between ground and the temp switch positions "TS" and "TF" on the fuse panel. If you have continuity, the thermo switch is calling for fan operation. If the car is cold, the thermo switch is bad. Conversely, if the car is hot, and you do not get continuity, the thermo switch is bad. The thermo switch tends to fail safe (it calls for fan operation all the time). This will kill the battery, but save the engine. A good tradeoff in my opinion.

3. Fabricate a jumper wire with flat blade connectors on each end, and a 20a fuse in the middle.

4. Connect the jumper between M1 30 to M1, the drivers fan should run at high speed. If the fan does not run, check for voltage in the connector at the fan motor, if you have voltage but the fan does not run, replace the fan motor.

5. Check the passenger fan by connecting the jumper between M2 30 and M2, the passenger fan should run at high speed. If not, the same drill.

6. Next connect the jumper between M1 30 and V1, the drivers fan should run at low speed. If not the resistor or wiring is bad. Check for voltage at the radiator fan connector and then check the resistance across the resistor.

7. Next connect the jumper between M2 30 and V2, the passenger fan should run at low speed. If it does not run, check the wiring and resistor.

CyCloNe!

My next mission is to get a fan relay, replace both temp sensors (clean connectors) and maybe the thermostat and see if I can get the mark down. I tried repairing the relay but it appears there's some damage to the board in a few spots, I went ahead and re-soldered all the pins but when I tested it in the car there was no change, I know there was atleast damage on the a/c switch portion.

CyCloNe!

well I decided to do a little test, if I jumped the fans so both come on low speed would the car still sit on the high white mark? Well I did the test and it took longer but still went right at the mark maybe a tad lower. I turned on the heat full blast and the gauge went way lower between the mid and top white mark closer to the mid mark. So if cycling coolant using the heater on high made it cooler I guess I'm still looking at a thermostat or a restriction in the radiator?

I'm going to try a new gauge temp sensor and get a fan relay first to see if that helps and if not then I'll try a flush and new thermostat.