Charge Air Cooler

[Jon Wehrenberg]

I don't have data for the bus engine, but for the plane engine a 35 degree increase in air temperature equates to a 5% loss of power, but a reduction in fuel flow.

The point here is that on very cold days the bus will produce more power, and there will be an increase in fuel flow adversely affecting mileage. If the charge air is overheated power will be down, but to maintain a given speed compared to cold temperatures fuel flow should be less, increasing mileage.

That is on a plane with mechanical power adjustments. I don't know if the DDEC on the bus adjusts fuel flow to compensate for charge air temperature. The black smoke may be an indication that fuel flow is a function of the throttle position only, although I was under the impression there was some compensation for turbo boost.

I'll be interested in hearing Jack's opinion on the fix and its impact, also what has changed on Roger's coach causing the black smoke. If there is no temperature compensation in the fuel flow then Roger's issue may just be that the warm temps are not providing sufficient charge air density to burn all the fuel under throttle inputs. So far we have had a relatively cool summer.

[jack14r]

Jon,I think that fuel flow is a function of air flow prior to the turbo or throttle position,I am basing this on a situation I had the other day,when I left the DD service center a clamp just after the turbo came off and the hose came off and of course there was no boost and black smoke poured out.I think that a leak in the air charge cooler does not get seen by the DDEC and therefore the mixture gets richer and some black smoke comes out the tailpipe.Roger asked about fuel mileage and mine was 5.3 a year ago and has drifted down to 4.6,I believe that the air charge cooler was cracked when I took delivery of this coach.The performance was never equal to my 05 coach.I am looking forward to seeing how much the performance changes after the repair and I will report back.

[jack14r]

Covington Detroit Diesel installed the new air charge cooler today and the differences are immediate,boost on the gauge maybe 1-2 inches higher,mid-range power much better.I hope fuel mileage increases.

[jack14r]

After traveling 1400 miles I got between 5.5 and 5.9 MPG,I was also towing a full size 4 door truck.This coach has never gotten over 5.3 MPG with the truck behind it,so the air charge cooler must have been cracked since I took delivery a year ago.There are no codes that have shown up and the engine has much more response,I am considering buying a Silverleaf electronic display so I can see the boost in a digital display.

[Pete]

What has your experience been with shock replacement? I have an occasional "bounce" that can be felt in my seat back. It is not constant, nor prolonged when it does occur..it can occur on smooth road, then goes away. I thought I would have the shocks replaced and called Prevost to order a new set and was told they only replace them when they show evidence of leakage. I don't know if they have ever been replaced, and can't get under the coach to look at them. I was wanting your opinion as to shocks getting "weak" and needing to be replaced even though they show no sign of leakage. I have a tendency to believe that they can get weak with age. My coach has about 113k miles.
Andre seems to agree, how about more opinions?

[stevet903]

I have an 89 with 117K on it that I replaced all of the original shocks on, and the difference in the ride was not subtle. It was much more controlled, less lean around corners and less of a smash going over big bumps. Only one appeared to be leaking, but a comparison to the new ones showed that each of the old ones that came off had differing degrees of resistance (some had almost none!!), even without leaking. They are fairly easy to replace yourself and if I recall, one of the cheaper things you can get from Prevost (about $50 each). Soak the nuts in your favorite penetrating oil for a couple days before hand and you should be all set. Now for the bad news.... If you haven't yet, your radius rod bushings are probably old enough to be dry rotted and in need of replacement. Ditto for the airbags. Putting the bushings in the rods is easy. Getting the rods off the bus to put the bushings in is not, and potentially dangerous since there are heavy pieces (rear end, front axle) that need to be supported while the bus is in the air. I think the bushings are about $5 a piece, but you will probably need 30 or 40 hours time to do them all front and rear. To do shocks, air bags, and bushings will probably knock a good hole in $7500 at Prevost.

[hhoppe]

My sugestion would be to ask truck operators around your area or a larger town for a name of the best truck alignment shop. Thay will have a pit, can change all worn front end parts, they will adjust the tension in your steering box, install the new shocks, and do the chasis alignment. If done correctly you will feel like you are driving a new bus. No more corner leans, porpusing or loose steering wander. Prevost offers two choices of shocks, regular and heavy duty. Choose the H.D. ones. Their prices are reasonable and you will get the correct ones to fit your bus. The ones they sent me were "Monroes". DSIUY

[jelmore]

My sugestion would be to ask truck operators around your area or a larger town for a name of the best truck alignment shop. Thay will have a pit, can change all worn front end parts, they will adjust the tension in your steering box, install the new shocks, and do the chasis alignment. If done correctly you will feel like you are driving a new bus. No more corner leans, porpusing or loose steering wander. Prevost offers two choices of shocks, regular and heavy duty. Choose the H.D. ones. Their prices are reasonable and you will get the correct ones to fit your bus. The ones they sent me were "Monroes". DSIUY

Harry, I'm going to visit a big truck shop Monday or Tuesday. I don't like the wear in my right steer. I had an alignment a year ago and that corrected everything. The bus drives and tracks just great since then. Will this truck shop know what shocks to install if needed, or do they need to be ordered from Prevost? What does DSIUY mean?