My 99 Caravan (3.3 L Flex fuel) starts knocking every time the radiator cooling fan kicks on. It does this whether A/C or headlights (i.e. other engine load) is on or not. I know it is related to the fan or fan circuit, since it stops knocking immediately when the fan shuts off and starts immediately when the fan turns on. If I yank the fuse to kill the fan, the knock stops immediately.

I'm going to change the relay (cheaper than the fan assembly) and see how it does.

Anyone have any other ideas?

 

Replace the fan assembly the relay will not cause it to knock

 

I may try to replace the fan assembly, but do you know why a fan assembly (or relay for that matter) would cause the engine to knock? A dealer service department told me that for some reason it sounds like the computer is changing the timing or something whenever the fan comes on, but he wasn't sure about that.

 

The cooling fans put quite a big electrical load on the engine. It sounds like it may be an overly advanced igniton timing at idle, a loose or separating crank pulley/damper, or a lean fuel mixture at idle. I doubt it is the fan assembly itself but rather what the load does to the engine. The headlights don't draw as much power. How many miles are on it and what type of driving do you do. Sometimes excessive carbon build up can cause detonation at idle. Have you looked at the plugs lately to see what kind of shape they are in and what color they are?

 

thanks for the tips. i decided to replace the fan assembly. bought one at Advance for $200.
since there are 2 fans, i tried disconnecting them one at a time to see if one side was causing the problem.
as I was looking at the fan, I saw a 5/8" combination wrench down inside the fan housing. I took it out and just for kicks reconnected that fan (which had been the one causing the knock). To my great surprise, the knock is gone! I ran it again today and could not get the knock to return.

I think the wrench was rubbing the fan just hard enough to draw too much current, but not hard enough to burn up the motor or blow the fuse. Crazy.

I'll keep the new fan assembly a few days to be sure it's working ok, but I think my problem was a wrench someone had dropped in and left.

Thanks again.

 

WOW--I hope that wrench was a Craftsman

 

sadly, it was not a craftsman...

 

Could it have possibly been the wrench hitting the fan blades and causing the knocking sound?
These fans are balanced pretty well from the factory and need to stay that way,so be sure the fan doesn't vibrate itself to destruction.

 

lmao.. good on ya.. glad you found it.. im betting however.. it wasnt the engine knocking.. rather it was either the fan hitting the wrench.. or the wrench hitting the frame or the block.