-
It’s Not the Fan Clutch
I had just started my day’s travel a couple days ago and noticed my engine temperature was climbing to 207 degrees. Although 207 degrees isn’t too hot, it’s hotter than the bus has ever run. There was nothing about the terrain or outside temperature that should have had the bus running hotter than normal. Knowing there was a pull off less than a 1/4 mile up the road I pulled off. The temperature was holding steady at 207. When I opened the engine bay doors the fan was barely turning.
We were in the Yukon Territory. For those not familiar with the Yukon, there’s not much here. It’s remote enough that the last 2 campgrounds produced their own power. Kudos to Prevost for including the ability to lock the fan clutch. In a matter of minutes I had the 4 bolts moved to lock the clutch. On we went to Haines Alaska, about 150 miles up the road.
I used the trubleshooting method that deenergizes relay #79 (broke off tab #85). Doing this the fan clutch did lock. So, it wasn’t the clutch. Unless the relay contacts just didn’t make a good connection, I’m not sure what to look at next. I did go down to the local NAPA store and they going to try to order new relays. If they are successful, they will be here next week. I assume the sensor the engine uses to engage the fan clutch is the same one that is giving me my display temperature. If true, the sensor must be good. I know it can’t be a fuse or circuit breaker because the fan clutch is engaged when the control voltage is removed from the relay.
If the relay doesn’t fix the problem, what’s the next thing to look at or should I feel confident it’s the relay? We have a little time yet. We’re parked until we can get on the ferry on the 20th.
Thanks,
Gil
-
18 Replies
-
What you did was over ride the DDEC command to engage the clutch.
If your temps went down after you locked the clutch you ruled out the engine thermostats or a plugged radiator. I am assuming coolant level was not an issue.
So right now you still don’t know if it was the clutch or a clutch relay or some other reason why DDEC isn’t turning the fan on.
-
Jon,
Coolant level is good. I believe I also ruled out the clutch. I installed the modified relay (tab #85 removed) and turned the ignition switch on without starting the engine. When doing this the fan clutch did engage. I know this because it wouldn’t move.
Given the command to turn on the fan clutch is to turn off the power to the relay, I’m hopeful it’s just poor contacts on the 14 year old relay. FWIW, the clutch was replaced before I bought the bus. I’m guessing that was 20K miles ago.
Gil
-
Gil, hope it is just a contact, do not know what the life of these fan clutch’s are, mine went out at 69000 miles, since you only have 20000 on your clutch would not think that to be the problem. At least your are mobile! Gary
-
Just swap the relay with one you are not using at the moment and see what happens.
I keep a bag of relays in my spares. Prevost had the best prices by far and their relays are equipped with a resistor making them ideal for the coach.
-
When on the road and chasis parts are needed, the best practical source is “PREVOST”.
Just sayin. JIM
-
Gil,
If the relay is the same, you have one that turns on the brake lights everytime you use the jake brake. I forget the number, I always remove them, but that might work out as a spare for now. It’s also in the rear run box.
-
The replacement relays are due in Tuesday or Wednesday. I’ll see if they work.
-
Jon what is the resistor for on the relays?
-
Greg,
I think they suppress voltage spikes. It is a long time since I was told the reason why so that might be the wrong answer.
-
It also could be a kick back diode. Here’s a long description of a relay and it’s function, more than most anyone needs to know.
http://www.bcae1.com/relays.htm
Ken
-
Excellent post and a link I have bookmarked.
-
Thank you, Ken, that’s a great link. I never would have looked for it on my own. I made it down to the part about diodes before I reached overload for now, but am looking forward to being able to use that new knowledge to speak more intelligently about some things on PC now!
-
Great link, thank you…
Jon – Let’s put this in the Article section?
-
Absolutely, and can we make sure Ken gets credit? That one is a winner.
-
Thanks for that link… great reading….I have a whole new respect for relays now !! They do a lot more work than I ever imagined.
Diane
Log in to reply.