Fan Troubles

[galaxie428]

My fan quit working some time ago on my M998 but I'm just now getting around to troubleshoot it. Previously, it started cycling on and off quickly one or two times, then would stay on to cool. But it would come on early, somewhere around 190-195 so it was running pretty much constantly once that temp was reached. Now it doesn't come on at all unless I unplug the time delay.

I've gone through the diagnostic flowchart down to this page. I'm assuming by "voltage", they mean 24v? If that is the case, it leads me to the transmission. However, it just sends me to the general section of troubleshooting the transmission.

For additional info, I'm in the process of swapping the 6.2 to a 6.5TD which is done and also the trans to a 4L80E which I'm waiting on. This was an issue before I started the swap though so I don't think it's related. I did not change my body harness as I'm going to use a stand alone controller for the trans and I'm using my original engine harness on the 6.5TD. So I do have the two plugs for the kickdown that are not connected to anything at the moment. Like I said before, this was an issue prior to the swap so I don't think it has anything to do with my issue now. But, I wanted to ask the experts.

Any thoughts on additional tests I can do or is there a likely component causing my issue?

 

[galaxie428]

Just a follow up on this since there were no responses, I think I'm going to try going through the diagnostics again this time with the computer out there in front of me so I don't miss anything. There has to be a step or something that I didn't test correctly.

 

[DREDnot]

First thing I would look at it the fan thermal switch by the thermostat. Unplug it and check for continuity cold. if its open (no continuity) when cold its bad. It shouldnt be open till the engine is near 230 degrees. That is what tells the fan control box to lock up the fan clutch. If it tests good then the next likely cause is the fan control box itself.

If you need to replace it, find an OEM switch. The cheaper ones are Chinese and have inconsistent opening temps and fail quickly. Always use OEM/NOS for controls and sensors.

 

[galaxie428]

Just to follow up, it did end up being the fan thermal switch. I switched it out and now my fan is coming on at 220. It does seem to shut off a little quickly at least according to my gauge. It's not even getting to 200 before it shuts off. I have a laser temp reader I'll try to check it with. Maybe the gauge isn't accurate.

I did find a really good video on youtube that helped me troubleshoot in addition to the TM.

 

[mgFray]

For comparison, mine kicks in right around 220, then off at about 205. 6.5L - V belt unit..