F355 Cooling Fan Issue

Yes, it looks strange but this appears to be just the way how the fan operates with the 88/82 C thermo-switch. In addition to my 348 experience with it, another member reported the same "behaviour" on his 348.

 

Properly operating LH fan. Car idling on a summer day. Posted this several years ago.

 

^^^^not able to view? shows private

 

OK, this makes good sense. I can rest well: my cooling fans are working properly. thank you. Amen. Now, onward to my cool (165') cruising temps...LOL

 

Now should be public

 

^^^^Thanks. I love the tell-tales. nice video.

 

With the location of the fan switch being on the radiator I believe that this is the cause for the rapid cycling. As the hotter coolant rushes by the switch, it triggers the switch to on. But then the running fan lowers the temp of the coolant that is rushing past the switch thus causing the switch to open, shutting the fan off. If the switch were located further away from the radiator on the inlet side, then the cycle time would increase. At least that is way I see it.

 

makes a lot of sense.

 

I could be wrong, but I don't think it works that way. The switch at the top of the radiator should be sensing the temp of the coolant entering the radiator from the engine, not leaving the radiator. If the coolant leaving the engine exceeds 190 the LH fan comes on, triggered by the thermo switch in the LH radiator. It switchs off when coolant leaving the engine is below 180. If the LH fan isn't sufficient to keep the coolant leaving the engine below 198*F the RH fan kicks in as signaled by the ECU based on the NTC sensor in the coolant manifold on the engine.

 

I know logic would have us believe that the switch on the top of the radiator would be constantly reading the temp coming from the engine. But my theory is that it does only until the fan kicks on. Then the cooler coolant is mixed in with the incoming coolant causing the short cycle. I guess my entire point lies with the exact placement of the switch is the culprit. If someone wanted to rig another switch into a different location and temporarily wire it to the existing plug, then it could be proven. (or disproved)

 

Some cars tend to do it before the car gets really hot as in driving. Idling when cooler or in the garage it tends to do that. This is where adding a the PWM (like modern cars) helps to soften the surge btw, when those fans kick on they draw the full 30 amps and if it happens with both its a huge draw. If it happens frequently the fuse box can develop heat issues and cause all sorts of problems. My lights no longer dim when the fans kick on, its a 348 cut pretty sure the355 has the same challenges there.

Just a reference, Miroljub get the credit for it, I just did it on mine too.
https://www.ferrarichat.com/forum/threads/implementing-cooling-fan-pwm-controller.608170/

 

The incoming coolant comes in on one side and the cooled coolant goes out the other. Just how to they mix? I would assume the top tank has a divider in it so that 1/2 the core is down flow(from the inlet) and the other half is up flow (to the outlet). Otherwise there would be very little flow through the core.

 

Not sure of the internal structure, but for what it's worth... the outboard pipe on top the left hand radiator is the cooled coolant. The switch seems to be on the outboard side (but just outboard of the centreline)

 

Image Unavailable, Please Login

I guess the sensed temperature would depend on the speed of the coolant flow through the core. If it was relatively slow, the coolant in the radiator would have time to cool and the fan would have the greatest effect on the coolant in the tank (and the temp sensor), but the engine itself might not get the cooling effect fast enough (at least at idle).

 

Yes, my error. They are monitoring the temp of the return water on the LH rad. Even more reason why gauge temp would not reflect fan cycling.

 

Yes, thanks Ian. If the switch were located in pipe "13" I think the fan would run until the coolant coming back from the engine reached 180, going along with what John mentioned in post 34. Just fabricating a tee to fit the switch into the branch would do the trick, and the wiring would probably be long enough to reach the new location. I'm sure cars in the hotter climates would benefit from this mod more so than cars here in New England.

 

John, if you neglect the small change in heat transfer coefficient with water temperature, the radiator with fans blowing has the ability to remove xx BUTs/sec/lbm from the coolant at a given air temperaure. For a given coolant flow rate that is equivalent to a specific temperature difference between inlet and outlet, regardless of coolant temperature, assuming the coolant is much hotter than the air. The point being that the same result can be accomplished by using a temp switch with lower set points. Other factors need to be consider, but that's the simple look at it. Also, looking at my 308 manual, it also places the fan switch on the outlet side of the radiator.

 

There is no need to complicate things by moving the thermo switch to sense the coolant coming from the engine to the radiator. If you want earlier switch-on of the fan(s) and running for longer between on and off, just replace the existing switch with one that has lower on-off points. There are plenty choices of switches having the same M22 thread. They need different connectors but that would not be a big problem.

For example, the Calorstat-Vernet TS1769 (Peugeot, Citroen, I think) is a dual switch 88-84 and 83-79, so you have one range for summer and one for winter. And this thermo switch uses the standard Bosch 3-pin connector which is easy to get:

Image Unavailable, Please Login

Or you can have slightly different temp ranges:

Image Unavailable, Please Login

 

If there is a need to complicate things, you could add a Pulse Width Modulated Fan Controller that would control the fan speed from a wide range of speeds. This would be the smoothest operation as you wouldn’t hear the rapid ON/OFF cycling of the fan, it would also reduce strain from the alternator from large amp spikes Essentially a technology that is installed in most cars today.
Image Unavailable, Please Login

 

Being that these cars are not know for overheating, what's the point? Another case of trying to fix something that ain't broke.

 

Its not the overheating though, its the heat in the fuse panel from constant 30 amp draw at frequent intervals and the accompanying electrical dip when they kick on. This is Miroljub's fuse panel he had to repair that is the LH fan relay. The PWM eliminates the annoying dip and the heat. Rare condition? Perhaps... But it will never happen on mine and my radio and lights no longer dip when they kick on and they both kick on at the same time in the 348. To each his own of course.

 

Yeah, I wasn't about to run out to my garage to start dismantling my car for sure. I was just pointing out that the answer to this thread lies in the poor design from the factory. They should have caught this before they started to mass produce these cars. I do like the PWM answer as it definitely would help the cars electrical system out, but I tend to be a purest so unless the problem becomes bad enough to potentially cause harm I will leave it as is.

 

I don't know that it's poor design. Yes, the fan cycles at idle but remember the system isn't designed for idle conditions. It has to have the capacity to cool under max load conditions at high RPM where the heat generation is a lot higher and where the RH fan will kick in as well. If I go out for a hard drive on a warm summer day, when I pull into t he driveway the LH fan is typically running and stays running for some time. Remember, the fan kicking on at 190 doesn't mean the coolant coming in never gets hotter. Newer system have variable speed fan and controlers but I don;t think anyone was doing that back in 96-99.

 

964's have this for the oil cooler fan and they came out in the late 1980's. Comes on low-speed (IIRC) around 190F and high speed around 210F.

I'm gonna be swapping my left side 355 fan for the Spal 30102050 model. Seems like a very easy way of dealing with the amp spike problem while also getting a much more reliable fan. I live in Los Angeles, there's no way to avoid getting constantly stuck in stop and go traffic here.

 

Looked this up....interesting, but seems complicated to install and calibrate. Set up right it's probably pretty great.

https://www.summitracing.com/parts/der-16795