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
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.
Gil and Durlene
2003 H-3 Hoffman Conversion
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.
Gil and Durlene
2003 H-3 Hoffman Conversion
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.
Gil and Durlene
2003 H-3 Hoffman Conversion
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.
Last edited by Joe Camper; 08-05-2019 at 05:53 PM.
1990 Peterbuilt 377
3406 B Caterpillar
13 Speed Roadranger
No Norgrens
1 day on paper no machines
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.
Last edited by Joe Camper; 08-05-2019 at 11:02 PM.
1990 Peterbuilt 377
3406 B Caterpillar
13 Speed Roadranger
No Norgrens
1 day on paper no machines