355 Cooling Fans

Not sure. The right hand fan is controlled by coolant (water) temperature, not specifically oil temperature. If the oil thermostat was toast, the coolant temperature (on the gauge) would be rising, too.

 

I went on a drive this evening throuhg the canyons. On my way to the starting point on the highway the oil temp was perfect. The fan fuse didn't blow and all was good. In the canyons driving reasonably hard, the oil temp got pretty close to the last black line. In fact on the way back even not driving super hard, the oil temp stayed at the notch above middle. I went to dinner and then drove home and on the highway the temp was perfectly fine. The fan fuse is also still fine.

Any thoughts on this??

 

Not sure which rads people mean when they say left and right (depends how you face the car) but I'm pretty certain the fan with the a/c in front is controlled by coolant temp and the fan with the oil rad is triggered by oil temp...
Regardless, fans only make a difference when stationary. When moving, its the airflow into and over the cr which cools more than the fans. If temps are rising when driving, I'd be looking elsewhere than fans.

Just my 2c...

 

The Left Fan is controlled by relay Q (relay S on the 2.7). The coil of relay Q is controlled by:
1) >15 bar refrigerant gas pressure switch on the AC receiver dryer OR
2) Thermoswitch on the LH Radiator

The Right Fan is controlled by relay R (relay T on the 2.7). The coil of relay R is controlled by:
1) The Motronic ECU which is triggered by the NTC coolant temperature sensor on the right half of the coolant manifold (in the engine "V") after the coolant leaves the engine and prior to the coolant reaching the oil cooler. The oil temperature sender does not input into the ECU or into the Left or RH fan circuits.

The coolant circulating in the engine leaves the engine and goes through the oil cooler then to both radiators via the thermostat.

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When the engine is hot, the coolant is circulating through both radiators.

How can you really define what is controlling what fans? If the engine is hot, the coolant and the oil is hot. The thermoswitch on the RH radiator and the NTC temperature sensor on the engine coolant manifold are both triggered by coolant temperature (i.e. overall engine temperature). The only thing which can override this is the refrigerant gas pressure switch on the receiver/dryer.

 

well, every day is a school day.
That's why this site is so great, there's some really amazing knowledge in the crowd.
Thanks for that!

 

If I don't care about how long it takes for the oil to warm up, can I run the car with the oil thermostat removed?

 

Dunno. Problem is it may never get to temp, which causes issues with viscosity / lubrication plus you never burn off anything out of the oil as it doest reach evap point so it becomes acidic which isn't ideal either. I also don't know whether oil temp alters timing of fuelling, although the schematic above would imply the ecu doesn't use oil temp so should be independent.

It's easy to check, just undo the big 36mm nut, copper crush and spring and then pull the stat out. if you can't then remove the whole assembly from the side of the tank (4 x 10mm nuts) and stuff a rag in the lower hole 9oil level should be below there anyway). then remove the stat and see if it slides easily in the housing and also if it extends its rod in boiling water.

should extend about 30mm around 93 degrees (I think)

 

I believe this is the part I need? 235648 - that should be the thermostat for the oil tank?

 

I removed the whole unit and it definitely moves. around 200F. Could it be the sending unit?

 

Are your fans still working? The trigger for the right fan is the sensor in the engine V (at 203degF/95degC). The trigger for the other fan on the LH radiator may depend on what thermoswitch you have fitted. I think the standard is 190degF +/-3degF (88C +/-2C)... with the aircon switched off.

You still haven't said what engine management system you have: 2.7 or 5.2? Maybe you could add this to your profile.

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Ahh sorry - I'm a 5.2 car - '97gts.

Both fans do come on - LH one cycles with the water temp correctly and water temp has been fine. RH one seems to come on around 100-150F and seems to stay on and not really cycle. Under normal driving around town and on the highway, oil temp sits at middle and creeps up to the next notch up on the gauge. When I did a canyon run the other night, it was basically at the last notch before red.

 

Strange. There seems to be two issues here. Your RH fan is on before it should be and running too long (possibly a sensor issue), but it doesn't seem to be cooling the oil.

Blocked heat exchanger? Oil thermostat? Partially blocked RH radiator?

Heat exchanger (Item 51) and coolant temp sensor (item 40) shown here:

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Since your left hand fan is behaving normally, the water thermostat seems to be operating normally (as hot water is reaching the radiators to activate the fan thermoswitch on the LH radiator). Thermoswitch not shown in diagram above.

I suppose there could be an oil pump issue, too. Insufficient flow to cool down the oil. Have you changed your oil filter recently?

I'm worried that if you do fit a serviceable coolant temp sensor (Item 40) that the RH fan will turn on less and your oil will get even hotter.

Experts?

 

I did check the oil thermostat today - I pulled the housing and boiled it in water - right at about 200F it opened nicely and closed nicely as well.

I just got the car back from my annual - so oil is fresh as is the filter. We also just replaced the RH fan as he thought the old one wasn't pulling enough.

Oil pressure seems good.

 

My mechanic also gave me a temp gun so I'm going to take it back to the canyons and see how it behaves then check temps at the tank fittings to see if the guage is accurate.

 

I thought I'd carry out an experiment with my NTC Coolant Temperature Sensor circuit to see what resistances triggered the RH fan on my car. I pulled the plug on my temp sensor and put a decade box (variable resistance) across the plug pins. I turned on the ignition and varied the resistance. Unfortunately, I couldn't get any resistance to trigger the fan

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I used a range of values between 330 ohm and 10 ohms

Is there more logic involved in the 5.2 fan control circuit? Does the engine need to be running for the fan to work? Or is there a timer circuit? I can't start my car at the moment. When you get the car warm enough to trigger the fan, if you shut off the engine and immediately turn the ignition back on but not start the engine, does the fan run? I can't remember.

Maybe my fan has just broken.

 

I confirmed today that you can simulate coolant temperature with a resistor, but only with the engine running. My fan worked normally. I was working in a confined garage and couldn't spend a lot of time playing, but the trigger point was about 190ohms.

 

There is probably some delay programmed in the ECU to avoid the fan coming on for a short lasting rise of the coolant temperature and/or to avoid too frequent fan switching on and off. If you keep the selected resistance, say at about 210 ohm (95C if the CTS is Bosch 0 280 130 026), the fan may be switched on after a couple of minutes. Table for Bosch 0 280 130 026:

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