Engine temperature

Recently on a trip to Dallas from Houston, I noticed the engine ran cooler when I turned the dash air on. Is this because the radiator fan increases RPM when the dash air compressor is engaged?

Fred

Yes, on most models. Prevost dash air engages the fan in high speed after a short time delay.

On cooler days with dash air on you should see the temperature fluctuate in response to the thermostats cycling.

I know this is an old thread but I just got our 1999 CC back from the Prevost shop in Fort Worth where they replaced the dash air compressor. We drove it for a couple of hours in the morning with the dash air on and engine temp was 195 or so. Out side temps were probably in the 80's. On the way back later that afternoon, the outside temp was 97 or 98 and in the hills engine temp was pretty close to the 220 tic mark ... call it 215. If we turned off the dash air, it would cool off by about 10 degrees or so pretty quickly. So in our case, it is running much warmer with the dash air on. Has anyone else experienced this?

By the way, Jason with Prevost Fort Worth did a fine job and took great care of us.

Your symptoms are pointing to a loose drive belt on the 90 degree gear drive. I'm surprised you didn't get a check engine light.

They seemed tight to me. I am going to check again now that it is cooler and double check the tension system air pressure. Also will check to see if the fan goes to high speed.
The dash temp gauge may also be reading higher then the DDEC. I need to see if there is a difference between the dash and gauge in the engine bay as well.

I take it that you did not expect it to be running in the 215 range?

I can't imagine the air conditioner preventing the fan not to engage the high speed fan clutch setting, especially when it's suppose to do so on it's own after the timer expires.

I certainly would not expect the engine temperature to rise because the the air conditioner clutch is engaged. If Prevost dash air raised the engine temperature with that little compressor can you imagine the impact on engine temperature with the huge 6 cylinder Bus Air compressor.

My thoughts exactly. The load would be inconsequential to a 500 hp engine.

When you've got OTR A/C the condenser is over in a bay on the other side of the bus. With Dash air only the condensers there by the radiator and the radiator catches all the hot air coming off the condenser.

Agreed... but do we think that the condenser temperature is enough to raise the engine temp 10 degrees or more? It doesn't seem like there could be that much thermal energy compared to what the engine is already delivering to the radiator.

I think it will. I chauffeured a barrel Rider who had a Liberty with over-the-road AC through Texas and Oklahoma a few Summers back it was a very hot summer. We were pulling a trailer with a horse in it and that poor bus was north of 210 ALL SUMMER LONG, had me real nervous all the time I hated it. I had that gauge burned into my brain I looked at it so much. If u would walk back there during short stops idling, heat was radiating off the engine room like it was a nuclear reactor. It never shut down or overheated not even once. That's where it ran.

My Prevo had over the road AC too. It was an 8v but it would run between 10 degrees+ hotter when I had the over-the-road AC going. 180 without 195 with ac on.

It's not really a good comparison to make with a non over the road AC bus but I think the same scenario applies even more so with yours cuz where the condenser is.

The over-the-road AC chassis pick up additional heat off the additional load of turning that gargantuan 6 cylinder AC compressor and on the non over-the-road AC coaches the extra heat gets picked up off the condenser.

I'm not sure what year coach you've got but the early 60 series coaches lacked a bunch of louvers above the engine bay doors that they inserted in latter years that cooled the engines down better.

I think also possibly once it gets North of 95 degrees or so all things change. If it were a more moderate air temperature the fact that the fan gets turned on high speed will get it cooler and it should, but, when it gets north of 95 outside all bets r off, the temperature goes up not down.

I never never never run in the heat of the day when its north of 95 and my current powerplant is a mechanical cat that never gets north of 190. Still won't do it, I'll go at night when it is and I have to get somewhere.

Mark I see you're from Arlington Texas. I'm currently doing some work on a Liberty in Lufkin and I'm going to be in Boyd with a CC the end of the week, that's just a little west of Fort Worth. Be there all weekend maybe longer.

Thanks Joe. We have family in town this weekend or I would drive out and say Hi! Good luck on the CC.

I've never seen or heard of the engine temperature increasing with Prevost's Dash Air on. In fact, most note lower temperatures given on most model years the fan clutch is engaged in the high speed setting with the air on.

Without the dash air off we will cycle up to 210 and then drop back down to 190 and then start all over again. With the dash air on (fan locked in) we rarely get above 205 unless we are pulling hills and most of the time are in the 185 to 195 range.

I still think once u get north of 95 outside things change.

Next time someone is out in 95°+ with a dash air only chassis we need to know how it does.

Joe, I've been there many times and still don't notice any increase in engine temperature. Of course, if I'm climbing a hill and trans temp rises, so does the engine temp.

Okay so I just went back to the current post that revived This Thread and he says I quote it was 97 or 98 and I was in the hills and it got to 215 I'm trying to assure him that there's nothing wrong with his bus those were within parameters for the conditions he was running in. can we agree on that?

We did a run from College Station to Houston (approximately 90 miles) yesterday. Outside temp was 102 with humidity to match (its hot but its a wet heat). I run 65 mph to 68 mph. The dash air was on the whole time. The engine coolant ranged from 184 to 189 (most of the time at 186). The engine oil temp ranged from 194 to 198 (most of the time 196). Finally the transmission temp ranged from 195 to 198 (most of the time 196). Even pulling a few small hills (southern Grimes County) there wasn't any change beyond the ranges mentioned. I did slow to 55 for a short stretch and that is when I got the low end of the range readings. I am not prepared to run the test in these temperatures without the dash air on for fear of divorce.

Based on that input I'd have to conclude that Fred's bus and the Liberty I drove for a summer, both coaches are running way too hot. Loc u need to pic up the pace just a tic.

Part II - I ran from Houston to the Hill Country (4 hours) starting at 3 am last Friday. Outside temp was 79 degrees to 77 degrees and humidity was Texas (always ridiculous) and I was running at 65 mph (slow down and see something Joe). Interestingly enough the AC compressor didn't run the whole time and I had temps significantly higher than my run in 102 degree heat the week before. The coolant temp would climb to 209 and then fall back to 185 provided I wasn't pulling one of the hills around Lake Travis (on a long climb it hit 211 but never over). Trans temp stayed in the 205 to 212 range. Oil temp got as high as 212 but then would drop down to 198. I came back Sunday afternoon in 101 to 103 degree heat with the AC on and the temps never got above 205 on the same road.

Thanks Loc. Seems like there is no Rhyme or Reason to some of your statistics. Repeating myself I drove a 60 series Prevo on a very very hot summer for two or three months and it ran at 210 constantly but it never shut down and it never overheated that's where it ran.

Thanks guys. I have been too busy to follow up on this any more. I am going to make sure the fan actually goes to high speed when I get a break. I dont recall it being as loud as some describe it when its on high. I was reading another post where someone added some small LED lights that indicated fan speed. That would be fun to have.

Loc, your results are very similar to those reported by others. I know my results on my last 99 and now on my 03 were very similar.

Thanks for the post.

I finally had a chance to look at this again. Before I started the diesel, I held the fan pulley still and could not rotate the fan. Then I started the diesel. As soon as the air built up to tension the drive belts, they chirped and the fan started to turn. It was blowing enough air that you had to hang on to the engine access doors when opening them. Then I turned on the AC compressor and the fan speed did not change. So it would appear that my fan clutched is locked in or perhaps replaced with one that is not two speed? I looked and did not see any wires going to the hub.

Also, I do not have transmission temp gauges etc. Does anyone have a recommendation for a meter that would plug into the DDEC to provide some real time information?

Are these fan clutches two speed? I've never had a definite answer to that question. My chassis has OTR A/C so no condenser in front of radiator. I've somewhat come to the conclusion that the "HIGH FAN" switch simply engages the fan clutch. Fan will spin otherwise ("HIGH FAN" off) but is simply freewheeling due to the fan drive spinning.

I have a relay socket in rear engine electrical cabinet marked "LOW FAN" but there was no relay there. When I had Carrier compressor shaft seal replaced by a charter bus mechanic I asked him about the empty relay space. He said he was pretty sure OTR A/C chassis didn't have a relay there. He put one in to check, nothing changed so left it for me as a spare.

If any of this is incorrect I'd like to know. Mine will get to 205-210 range without "HIGH FAN" switch turned on. That will bring it down into the 190's.

Mark,

Turn the ignition to off. Is the fan still locked? If so, there's something wrong with the clutch or it's manually locked. It doesn't locked locked as I can see the lock bolts.

If it wasn't locked in the last step, turn the ignition on but don't start the engine. Is it locked? If so, pull the low and high speed fan relays one at a time and see if the fan is still locked. If it's locked in either one, replace the relay or swap them to see if the one that locked it moves when you swap the relays. If a relay replacement does not unlock it you have a problem with the ground coming from the DDEC.

Billy, how did you determine putting a relay in the low speed slot had no affect on the clutch. I can't imagine what bus air has to do with the fan clutch as bus air doesn't need the radiator fan to turn.

Gil, bus was in shop on high idle when relay was put in. Fan was moving somewhat - freewheeling - that never changed. Nor has it changed since. Only way to bring engine temp down in the 190's is to turn on the "HIGH FAN" switch. Same as before additional relay was added.

I only mentioned mine has bus air so there wouldn't be any confusion regarding fan clutch engagement / dash air / radiator mounted condensers, which this one doesn't have. There was discussion earlier about the dash air system causing fan clutch operation - just wanted to be clear this one doesn't have any of that.

The wire lead is forward of the hub going thru a hole in a bracket forward of the hub. There r additionally 2 eyelets they run the wires through that r in a location that r impossible to loosen without pulling the whole carrage.

So often, removing the old one gets done buy cutting the wiring and pulling them out of the eyelets.

Ive seen countless leads on the replacement ziptied up to those eyelets because of this and worse yet just lying in there. Be sure its secure the leads r over length and can lay on the oil cooler if not sufficiantly fastened.

Joe,

The difference in my temps was due to the fan not being locked up. When locked up, the temps were very predictable even in high outside temps and the bus runs cooler than when the fan is not locked up. When not locked up, temps got up to the 210 level then the fan kicked in and brought them back down.

I checked the fan and it was locked up with the key off and both the 12V and 24V engine bay switches in the off position. I will double check this again this weekend to make sure. As I understand it, the fan has electo magnets and they will not lock up without power is that right? Assuming that is is locked up without power, is that an automatic replacement of the clutch or can we drive it and just not have two speeds?

Assuming that it is locked then that would be high speed so that would not be the reason for running a higher temp with the dash air one right? Unless the belts were slipping or something like that.

Mark, even though I could see the locking bolts weren't used, you should make sure the clutch does not have locking bolts installed. I've never heard of a failure mode where the clutch locks. And yes, it takes power to lock the clutch. Although it should not be powered with the key off, try pulling the main fan relay. I think it's R99 on your coach. Look at the relay decal on the door to make sure.

I agree with Gill. That hub with the red bolts clearly fastened is a 3rd gen hub. Tough to see what holes they r in, stored holes or locked holes. U could also remove all those red bolts and see if it frees up. If it does then confirm it kicks in like it should, could be its been locked in with good reason.

Another thing to check is make sure you have I believe it is 50 psi going to the belt tensioner bags. I see in the picture the your tensioner is very loose which is fine. But just makes me wonder if you have a major air leak not allowing the 50 psi to go to the bag allowing the belt to slip. My bus will go all winter and my belt bags are still have tension on them. Just a thought

Open your back engine bay doors and stick your head in there and look up at the back inside wall of bus and you will see a red handle there and beside that you will see what looks like a tire valve you would use to inflate a tire. Put a good digital air gauge on that and make sure you have 50 psi there.

Thanks, checking the air pressure is on the list. The picture you are referring to was with the leveling control in the dump position which I think releases air form the tensioning system too. After reading Joe Campers post on some of the front suspension boots being under stress in the down position I have started leaving it full of air.

Pulled relay 99 with key off and clutch still locked. Tensioning bellows did loose air. So two problems arghh. Appt with Fort Worth Prevost for a new clutch :-(

next time when I have more flexibility in my schedule I will try this on my own

lets hope this solves the AC temp issue as well

If the clutch stays locked, replacing it will not help over heating. Could you see 4 bolts, the size of the red ones, installed near the edge of the clutch near the fan. You see the bolts or open threaded bolt holes.

Open holes. Without taking it apart I don’t know why it’s locked up but it is not the red bolts. Assuming the fans been running in high speed it probably won’t fix the potential overheating problem but I’m not comfortable with the locked up hub and I have two 6 hour trips coming up

Here's a picture that shows 2 holes without the locking bolts. If they had bolts in them the fan would be locked.
Attachment 15762

That is the way mine look. Open holes no bolts

Very odd for it to be stuck locked. Also odd to experiance inflated running temps with it locked in those 2 things dont add up. Did u pull the relay? Did u check the wire lead to be sure is not unfastened lying on something hot and its been melted and shorted?

Reach in deep, over the top, forward of the bracket and feel the wire around toward the engine till u reach where it plugs in at the engine loom. Make sure thats happy.

Call P.A.S.S. see what they say and be sure to mention the inflated running temps too, if u do.