[Kenton]

Sammy, the real answer(s) will be offered by Bill Jensen of Prevost, but until he gets a chance to jump in here more information is needed. What you did not say were the conditions of driving, outside temp, hills?, speeds, and if this has just happened or have you noticed temps rising over a period of months.

Our engines have two devices that regulate temperatures, the engine thermostat and our DDEC controlled two speed fans. If your fan clutch is the cause there will be several clues. First, if it works intermittently as you describe, and you can pull a hard steep hill under full power and the temps stay 195 to 210 then you can likely rule out a plugged radiator. To go further, lock the fan blade to the clutch with the two 6MM bolts in the end of the fan drive shaft and go for a ride. With the fan locked (always engaged) your temps will cycle with the engine thermostat at between 190 and 195 indicated.

If that happens the culprit is likely the fan clutch or the connections might have some corrosion.

It’s Bill’s turn. He is the expert, but the trouble shooting is not that difficult. DO NOT RUN A HOT ENGINE.

If you need help learning how to lock the fan blad I think I can post some photos. Eveybody needs to know how to do that anyway.

[Archived]

The first time it ran a little hot, the temperature was probably in the mid 60’s, I was on a flat 4 lane road running about 50 and the fog was very thick. To say the least, there was a lot of moisture in the air. The time the DDEC unit showed 217, the outside temps and conditions were the same but I was on the interstate running about 65. I slowed down to pull over when the temp started going down immediately. Then the other few times I was out of the fog and the temperatures were probably mid 70’s. I did notice it started to raise a couple of times when pulling up hills but it would not get real hot at those times. Probably no more than 210. Thanks for your reply.

[Archived]

Sammy,

My coach is set so the low speed fan engages at 204 and the high speed at 208. If I use the gauge on the dash those numbers seem accurate. When I had a problem with my fan clutch I locked the fan blades and I watched the temps cycle with the engine thermostat from 190 to 195 so I could rule out any issues with the radiator, thremostat, water pump, etc.

Once you have ruled out other problems by locking the fan you can more easily focus on the problem.

[Archived]

Jon, If you could repost the pictures or article of how to lock in the fan that would be greatly appreciated. I have seen a picture/article before but can not find it at this time. Thanks for all your help.

[Archived]

Sammy,

I looked in my photo file and other files to see if I could find either an article or photos of how to lock the fan clutch. No joy. If I can get a break tomorrow I will take some photos and post them so it is clear how to lock the fan.

Hang in there.

[gary]

Sammy,

Below are the photos. You can tell I am not a professional photographer, but they should help you in knowing hopw to lock the radiator fan.

In the photo above you can see 4 zinc plated bolts. You may have two or four, but those are to be taken from the end of the shaft and used to lock the fan to the clutch housing.

That’s a lousy photo but if you look real close in the center you will see a tab with two holes in it. You may only have one hole in the tab on your fan. The tab is kind of ghost like in this photo but it is there. Rotate the fan and or pulley until the holes in the tab and the holes in the clutch housing line up, insert the screws and the fan is now locked. The tabs on the fan are 180 degrees apart.

With the fan locked you should see the engine temps cycle around 190 to 195. Drive up steep hills, do hard acceleration, pull a load. If the temps stay within that range it is unlikely the thermostat, radiator or water pump are bad and the probably cause is the fan clutch is not getting energized via DDEC, or the connections are bad or the clutch needs to be replaced or rebuilt.

You will want to unlock the fan and correct the problem because the cost of fuel at today’s prices can be $50 more per 1000 miles because the fan takes a lot of horsepower and the clutch disengages it every time it is not needed.

[Archived]

Thanks for your help. I will try this.

[Archived]

Thanks, Jon!

The advise you gave is correct and the method to lock the fan mechanically is correct.

We sometimes go to the rear junction box and find the two relays for the electrical functioning of the fan clutch. 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. If the temperture now stays regular and in line with what you were seeing then there is a problem in the control of the fan clutch.

If this does nothing to regulate the temperature ( and you know for sure that the fan clutch is locked in). then you would have to look at the radiator, both externally and internally.

When you have the tab off the relay and you simply turn on the ignition switch(don’t start the engine!), go to the rear and grab the fan blade. It should not turn as it should be locked in electrically. If it still turns but with resistance then I would look to the fan clutch as the problem.

Either way, Jon’s method of mechanically locking the fan with the bolts would enable you to get to the servie facility safely.

One caveat! This mechanical lock up is for use to get you to a place of repair. If you try to use it in place of the controls you will find that the tab(s) will break off and then you would possibly not have a functioning fan clutch at all.

If it just threatens to overheat , drive it to the service facility carefully watching the temperature. The normal safety shutdown on the engine for high coolant temperature will still shut off the engine to prevent damage.

[AL]

Thanks, I was remiss in not emphasizing the use of the tabs is a temporary thing to help isolate a problem. Unlike breaking tabs off a relay it can be undone with a wrench.

For owners who do experience higher temps and wish to assist the service folks when in need of attention to the problem you can be a huge help by doing temperature checks with the fan locked because you help zero in on the problem making the service both less expensive and time consuming.

[gary]

Never thought of the relays, excellent advise for getting to a service facitily.

Thanks Prevost…..

[Dale]

Thanks for all the advice. I will make an appointment with Prevost in Nashville and try to get it there. Not going to drive it anywhere else until I get it checked out and fixed.

[Archived]

Jon: Have you ever posted a how to on fan clutch replacement. I suppose it’s pretty straightforward; I see nothing in the maintenance manual.

I’ve been hearing a noise from that area while the engine is idling. This AM, I removed the drive beltand started spinning pulleys. Idler OK, fan OK, but I found the bad bearings when I spun the fan pulley. I’m assuming these are bearings internal to the fan clutch itself?

[AL]

Joel,

I did a write up on fan clutch replacement, and I’ll have to dig it up and post it if I haven’t already.

But here are the key points. First, take stuff off the weldment that holds the gear box so you can tip it all the way towards the engine. That maximixes the rooom while working on the fan.

With that structure tipped toward the engine the maximum possible, use a mirror to look at the nuts that hold the fan to the clutch. Remove them and just carefully lay the fan against the radiator. I think (have to find the procedure I wrote) you can remove a portion of the clutch that is behind the fan. I think it has some strong magnets so after you get the fasteners off be prepared to pry it free from the magnets with a pry or heavy screw driver.

Remove the pulley from the clutch, then disconnect the wires. The whole object is to strip as much from the clutch as possible because it is heavy and you are lifting with your arms outstretched. Remove the four nuts and bolts holding it to the welded structure and lift it out. Once you have it out it is easy to see how it all comes apart and goes back together. I wish I knew that when I did it because I removed it with the fan attached and my back paid the price.

Plan on a couple of hours. There is nothing above the clutch you can tie onto to use to pull it up or support the clutch so if you have back problems, bribe a neighbor you don’t like with beer and sacrifice his back.

[Scott]

I finished replacement on my clutch yesterday. I blew through the two hours of time allotted that Jon mentioned, just thinking about it. That sucker (replacement clutch) is heavy, very heavy. Holding the clutch with my arms extended was “toooough“. But I did finally get it installed, with much grunting. I have not tested it yet, but the replacement unit was different than the unit originally installed. The replacement unit was very heavy duty.

I stripped the Boston Superior gearbox out of the way, which gave me better access. While I had the gearbox out, I replaced the three oil seals on the shafts.

Hector

[Dale]

Hector,

If you took any pictures, please post.