Bus Engine Shutdown

[Jon Wehrenberg]

Tom et al,

The sensors cover DDEC coaches with the exception of EGR coaches. I have not found a diagram of sensor locations on 8V92 coaches, but if I do I will add that to the article.

Adding to Brian's previous post, there are three circuit breakers which handle DDEC functions in the rear electrical box. The numbers may vary, but on my coach they are 19,20 and 21. If those breakers trip the engine will not run either. Assuming the CB is not bad, however, merely resttting the tripped breaker gets you running again.

To all the new owners..............we are not trying to scare you and these sensor, relay or circuit breaker failures are not common, but they do happen. Nobody here needs to be an expert on this stuff, but only needs to be aware there are some component failures that can shut your engine down. There is no preventive maintenance that I know of, nor is there any way to predict if or when a part will fail. In every case however the diagnosis of what failed is fairly simple and a call to the Prevost or Detroit 24 hour help lines will often allow you to pinpoint the problem.

If you use your coach in the pursuit of business you may wish to study this topic a little and carry some spares.

[Jeff Bayley]

In order to prevent posting a new thread I just did a search for "coolant" and found this existing thead.

My sensors (ordered complete set at Jon's article suggestion) finally arrived today and installed what I belive was the faulty one but will road test tommorow. Now, while we were waiting, my wife keep saying, "What about the water........it could be low water.........we should add water". So I added a gallon of water to the overflow tank. It was half way at the site glass as the time of adding it. The conversation about "the water" continued. No amount of explaining would close the hole about how the ebb and flow of the water when hot and cold and that that overlow tank didn't need to be topped off. Finally, I couldn't take it anymore so to end the "We need more water there" conversation, I let her watch me dump yet another gallon of water in. This brought the level all the way to top and overflowed. I figured a half gallon or gallon would blow out through the overflow hose and I got to end the insanity. BUT, the cap went on and off sort of hard and I just got done reading Jon's coolant change article and it got me to thinking that if the cap fails to open and allow the water to purge, something else may give way and blow a gasket in the system. So I think I should siphon a gallon out tommorow before shoving off. I think the first gallon was ok to add to get it above the site glass but not the 2nd.

Can someone confirm if I'm correct to leave some empty space in that tank ?

[JIM CHALOUPKA]

I'll confirm that!

JIM

[Jeff Bayley]

I thought about it and don't think the cap needs to purge after all and in fact does not ever purge. I was thinking about the spring loaded cap and got myself mixed up but that spring is just helping keep the cap on tight, not opening and closing to allow the overflow to purge I'm pretty sure. I think when the overflow get's full, the water simply finds it way out through the top hose. Jeez, now if that's the case the system woudn't be sealed up and create preassure. Ok, back to needing clarification whether to let some water out and give the overflow some breathing room.

[Jon Wehrenberg]

The header tank, or surge tank has two caps on my bus. The lower cap is for filling and the upper one is not accessible for filling.

Both caps have a spring designed to hold about 14 PSI system pressure. If the system did not have pressure the coolant would boil prematurely. The pressure raises the boiling point which is a good thing because our coolant can get as hot as 205 to 210 degrees during normal ooperations.

Once the pressure exceeds the system pressure limits as determined by the cap, the bottom seal on the radiator cap lifts and excess water is purged out through the hose.

When you filled and overflowed the tank, there was still a small amount of air above the liquid level. I suspect however that when your 22 or 24 gallons of coolant is heated, it will expand and push the excess out the vent line on the lower filler neck.

[Jeff Bayley]

Thanks Jon. I almost understand the whole thing but don't quite get how the system builds up preasue when the vent line is below the fill cap. Yet I know it does because you get the "Wooosh" of air coming out when you remove the cap in two stages. I guess I just need to look at it again and I think it's a good idea to siphon a little out and leave the overflow tank half full instead of all the way full.

Also, I'm about to order more spare parts (I want to be like you.......prepared). I'm going to do the flush on the coach coolant per your article and I also noticed a posting somehwere in the last day of browsing for a relay.

Prevost Part 561991 is $11.19 (this relay is suppsed to be slightly different than the others and the writer says a good idea to keep an bus). Ok, the post was by BrianE and is on page 2 of this thread.

The Detroit coolant filter is a "Nalcool" filter part number 550630 and is $22.43 and Prevost Parts has it. While I'm at it, does Jon or anyone else recommend any other spare parts to order so I can get it all in on one order ? Already have belts of course but nothing else besides all of the sensors I just got.

[Jon Wehrenberg]

If you are ordering spare parts make sure they will work in your coach. Prevost has used several generations of relays for example. I don't know what relay you refer to, but my current coach does not use the same relays as my previous coach.

[Darrell McCarley]

Jeff...........Just to add to Jon's comment. You should have a fill cap on the front side and a 14 lb cap on top to release antifreeze to a plastic overflow or a small hose to the ground when your pressure gets above 14lbs. I fill my tank all the way to the top and let the pressure take care of the amount of antifreeze needed in the tank. The 14lb pressure cap on top will release pressure before you blow a gasket or hose.......Just some added thoughts.......Darrell

[merle&louise]

If you are ordering spare parts make sure they will work in your coach. Prevost has used several generations of relays for example. I don't know what relay you refer to, but my current coach does not use the same relays as my previous coach.

Today the DD parts guy asked me what my serial # was in order to get the correct sensors for my production year engine. I gave him the part numbers Jon posted and he will double check them against the ones for my engine.

UPDATE: All of the part numbers matched up with my serial #. Thanks Jon!

[Denny]

When I was at Williams Detroit Diesel ordering the above mentioned parts, the service mgr. also said that there is a sensor on the Allison Transmission that will stop the bus. I apologize that I don't have the part name or number because I told him I would take it. His recommending this was good enough for me since he knew that I was trying to be prepared in the event of certain failures. I will try and get a part number and better description if any interest is shown.