[Ed]

I made an appointment with Prevost in Nashville. They removed the radiator, had it cleaned by an outside vendor and put in new antifreeze. They also replace the thermostats. They told me my fan clutch was working properly. They test drove it and monitored it with their computer. I drove it back home to Tuscaloosa (250 miles), then a few weeks later drove it to Orange Beach, another 250 miles. No problems at all, as a matter of fact it ran cooler than it ever has, never got over 195 and the outside temperatures were in the low 90’s. Then leaving Orange Beach yesterday, maybe 10 miles down the road, the temperature guage started climbing and kept getting hotter and hotter maybe around 210. I was on the Foley Beach Express which is a four lane, with 55 MPH speed limit and very flat. I immediatley pulled over to check it out. I checked the engine guage and it was showing about the same. The fan was not running even though I had the dash air wide open. The outside tempature was about 78 degrees and overcast and I was headed into a rain storm a few miles away. I let it cool down a little while and then locked in the fan with the bolts. Drove the rest of the way home and never got over 195 degrees. Could this possibly be a relay issue? I know it could still be the fan clutch but I am hoping that I do not have to add that to the pile of $$$ already paid on this issue. Just frustrating that it seems to only happen when it is cooler and a lot of mositure in the air. I was within about 25 miles of where it happened last time. Advice???

[Dale]

Sammy,

Give Prevost parts a call and get a bag of 10 relays. They are universal and will replace any or all of the black cube relays on your coach. They are dirt cheap from Prevost and for the $5 or so apiece you can replace the fan clutch relays (2 of them, listed on the door panel decal) and see if the clutch has malfuncted (a very technical term) or if the relays are getting lazy.

You did not say if it was heading past 210. If it was then it could be the clutch. I think the first speed on the fan engages at 204 on your vintage coach and 208 for the second speed. I doubt if our gauges are so accurate or easy to read so from my perspective 208, 210 looks the same on the gauge.

[Archived]

I will call them tomorrow and get the relays.

You are correct about an accurate reading. My gauge goes from 195 to 220 with no marks in between, you just have to guess where the temp is at. I just know it was getting too hot for me and while I had a good place to pull over, I took advantage of it.

As always, thanks for your help.

[Archived]

Which relay do you break the tab off of, or do break the tab off of both? Thanks

[Charles]

Sammy,

When you turn on the dash air, there is a timed delay of maybe a couple minutes and then the engine fan comes on at high speed when the A/C compressor comes on line. The engine fan stays on high as long as the dash A/C is on. That would at least confirm your fan clutch is working properly. Like Jon said, relays are cheap and I replaced mine just as a PM item.

[Archived]

Charles,

Go back to the first group of posts on this thread and you will see Prevosts answer there. It’s blade number 85.

[Don]

Thanks Tom. I will certainly change out the relay and then test again the fan with the AC.

[Archived]

“You have relay R78 for low speed and R79 for high speed. If you pull the relay and look at the spades coming out of the relay you will see that they are all marked (30, 87, 87a, 86, 85). Breakoff the 85 tab from the relay andre-install it in the coach. This will cause the fan to be locked electrically. It will stay in high speed now no matter what the engine ECM tells it to do.”
Do I brake the 85 tab off of both R78 and R79 to lock it in high speed or just one of them?
DKO

[Ronald]

If you just do the high speed, it will lock in high speed.

[Archived]

Ok, still having issues after Prevost took the radiator out and got it cleaned, installed new thermostats and antifreeze. They said my clutch fan was working properly. I replaced both relays in #78 and #79. I left out last week and got about 20 miles down the road and the temps went sky high. I had the dash air running and when I pulled out of the driveway the fan was running. The DECC unit got up to 225 and the lights came on before I could get it pulled off the side of the road. I let it cool a little bit, then replaced the new relay with one that I had broken off the #85 tab. Cranked it up and drove a about 2-3 miles down the road and it started going up again. I pulled over immediately and locked the fan with the bolts. The temps went down immediately once I locked in the fan with the bolts and it never got over 195 on the gauge for the other 300 miles that day. So I am assuming the only thing left is to replace the fan clutch. Just was not sure why breaking the tab off of the relay did not lock the fan. Any suggestions or comments?

[Archived]

IT’S THE FAN CLUTCH, TAKE IT BACK TO NASHVILLE, SEPT. 1ST IS COMING UP QUICK DARRELL

[Archived]

Since this thread was from back in 2012, I can’t imagine that Sammy and Brenda haven’t repaired the problem. Still, I write this for those experiencing this same issue

From what I’ve read here, this is not a clutch problem. This is an electrical issue. When having a clutch problem and one replaces the clutch then still has the same clutch problem, it’s probably not the clutch.

They mentioned that they broke off that tab in the relay. (Probably not a good idea unless one has a spare relay to replace it with once the problem is resolved) That didn’t solve the problem either.

It’s likely that the problem will be found in a one foot stretch of wire located directly below the back of the turbo charger. This cable has a hi-temp insulated sleeve over the wires that feed the fan clutch. (Obviously it’s not hi-temp enough). The wires inside this sleeve will likely be melted together and will be making and breaking connection. This is why they had intermittant failures that Prevost didn’t experience while troubleshooting.

If you find this to be the case, run a new insulated cable on a path outside the area of that turbo. Often times this will permanently resolve the issue.

At ProFanDrive.com, we remanufacture the clutches found on these coaches. If you suspect a fan clutch issue, check out our website and call me (Bryan). I’d be happy to advise you at no charge.

I’d be interested in learning about any fan or compressor clutch related issue you may have resolved (or not yet) and will in turn, blog the solution out for others .

[Archived]

Sammy,

Here’s a previous thread on how to get the fan into high speed with the relay tab broken off:

Fan Relay

[Davy]

We did get it fixed a few months after the post. Prevost flushed and cleaned out the radiator and I wound up replacing the fan clutch which seemed to fix the problem. Maybe the wire was replaced too but it was not mentioned to me. I ran it for a little over a year before I traded up to a newer coach and had no further issues during that time. I did have extra relays as I always carry a few with me.

Thanks for your input.

[Archived]

In case anyone experiences what appears to be an overheating issue it is fairly easy to help diagnose the problem before bringing the coach in for service.

If you see temps rising and you know it is not because you are pulling a steep hill in 120 degree temps the obvious first thing to do is verify you have sufficient coolant. Don’t open the cap on a hot engine without taking precautions however.

If you have ample coolant, lock the fan. This thread covers how to do that.

With the fan locked your coach thermostat should be the engine temperature controller. With the fan locked your engine coolant temps should range around 190 to 195 degrees. You will see the temps cycling up and down within that range showing the thermostat is opening and closing as it is designed to do.

When climbing steep hills you can expect the temperatures to rise, however with the fan locked the temps might exceed the normal range of the thermostat, but should reach some relatively low temperature and stabilize. As you lift off the throttle, or the hill begins to flatten you should see an immediate drop in temps. But if your temps continue to climb start to suspect an occluded radiator or perhaps water pump issues.

If your temps start to approach 210 back out of it and let them cool down. Do not continue to push it. Heat is one of the quickest way to destroy and engine.

The fan clutch can fail. It can fail totally or it can only lock up in the low or high position. If you suspect the fan clutch is the issue locking it using the relays allows you to run long distances. If you use the tabs to lock it, they are designed for short term use and can break. Running with the fan locked to avoid replacing the clutch saves money in the short term, but it takes a lot of horsepower to drive the fan so eventually you will end up spending more in fuel than you save on a repair.