Fan slows down and speeds up like something slipping

[Tuesdak]

I am not sure what is going on when I have the fan speed audibility change with steady engine RPM and high ECT. I figure it's the belt to slipping or the fan clutch can't hold. I have not seen any solutions to some other posts about this. 3000 RPM towing a 6% grade with steady 227 ECT. I get different fan speeds and a weird faint noise when the fan slows down. Kinda a metallic bell and maybe screech noise. The time the fan slows down and then speeds back up is almost like the AC compressor running and then kicking out like it would at this RPM. The tensioner and Gates Greenback belt are fairly new with less than 3yr/30K on them. The idler pulley is also new with low miles. The fan clutch itself is unknown aftermarket or OEM, but, PO said was replaced at one time.

The high ECT itself may be from Evans waterless coolant as it has less efficiency than water. Like straight water cools better than high mixes of antifreeze. I also added a water cooled BB turbo heat load to the cooling system. Smarty tune on 3 and limiting EGT to under 1300 aiming for 1250 max.

Do I need a different belt or what?

 

[AH64ID]

Check for DTC's. If the ECM isn't seeing the fan speed it expects it can write a code that won't set the CEL.

 

[Ozymandias]

The Fan has a variable Speed. It isn't bound tonthe Engine RPM like the old ones.

 

[AH64ID]

The Fan has a variable Speed. It isn't bound tonthe Engine RPM like the old ones.

Correct, but at an ECT of 227° it shouldn't be variable and certainly not variable enough to hear. At an ECT of 227° the ECM should be commanding it to 100% of what it's programmed for.

 

[CJ8Rockcrawler]

I had something similar happen on our last road trip. I ended up replacing my fairly new serpentine belt that was glazed with the old one that I had in my boonie box and the problem went away. Check the simple things first. Just because the belt is new, doesn't mean it isn't the problem.

 

[Matt_L]

It could be your fan clutch. If your speed sensor is failing it can produce results like this....

Mine was doing the same thing, then wouldn't engage at all. All with no codes. When the mechanic hooked up the diagnostic tool, the speed sensor in the clutch was failed - it was indicating something like 9000 rpm fan speed at engine idle. Changed out clutch and all has been well ever since.

 

[BILTIT]

I had something similar happen on our last road trip. I ended up replacing my fairly new serpentine belt that was glazed with the old one that I had in my boonie box and the problem went away. Check the simple things first. Just because the belt is new, doesn't mean it isn't the problem.

I second this. I was only getting 13.0-13.5v charging and slow cranking problems, had alt. checked and was good. Swapped in my spare (old) belt and everything is back to normal.


Belts can cause issues.