| Author |
Message |
Mike Tornesello (66.82.9.23)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 11, 2003 - 8:29 pm: | |
I have an 8v92 in a 1988 Prevost.We drove from San Francisco to Denver arriving yesterday. After the last leg of the trip which was over Vail Pass, through the Eisenhower Tunnel and over Floyd hill going 35 mph at times we pulled into an Rv park and I checked the engine compartment after I shut down. The fan had been blowing black stuff all over the compartment. Engine oil is slightly below the add mark with engine warm. No warning lights or buzzers. No change in performance except some power loss possibly due to altitude. After the engine cooled I started it and found a significant exhaust leak in the main pipe right before the muffler next to the fan. Can it be possible that this is the source of all this black stuff? The Toad was muddy and black, somewhat from wet roads but it was oily and thick. You couldn't see out of any of the windows. Any guesses on this would be really appreciated. Thank you all.Mike |
RJ Long (24.127.74.29)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 11, 2003 - 8:45 pm: | |
Mike -
Did you notice a bunch of black smoke out the exhaust while climbing up to and thru the Ike Tunnel over Vail Pass? That smoke, combined with the slush off the roads, is probably what's all over your toad.
Be sure to check the oil level first thing in the morning, as it usually takes a Detroit at least 20 minutes to fully drain back into the oil pan after shut down.
Power loss is understandable at 10,000 ft!!
HTH,
RJ
PD4106-2784
Fresno CA |
Mike T (66.82.9.23)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 11, 2003 - 8:58 pm: | |
RJ, Thanks. I usually see black smoke but it was raining the whole time and I didn't see so much. Do you think that exhaust lead could make that much of a mess inside the compartment? Is all of that oil blowing by the rings because of high demand and low rpm? Mike |
Johnny (67.241.224.216)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 11, 2003 - 11:11 pm: | |
Oil everywhere? You mean that isn't normal operation for a Detroit?!
(sorry, but that was too good to pass up) |
Max (210.190.70.242)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 4:02 am: | |
Hey Mike,
What do you mean "High demand and low rpm"???
You should be pulling hills in low gear with the engine screaming at 2100 rpm, if your not your lugging and destroying your Detroit, its a 2 stroke and all the power is in the high rpm area not low down like the 4 strokes, but then again anyone with a 4 stroke would be pulling a hill in low gear turning high rpms because its easy on the engine. |
Peter (Sdibaja) (200.38.22.85)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 10:06 am: | |
Mike: I see no problem from here.
I see this in my bus whenever I climb long and hard or get over 4 or 5 thousand feet.
Many are confused about the "black and blue" of exhaust smoke…
To my understanding Blue exhaust is oil being burnt and blown out the tail pipe; Black exhaust is unburned fuel, actually soot, and it can be a bit oily.
High altitude makes for thin air and the air-fuel mix gets real rich. Climbing those hills and being at high altitude you were pumping more fuel into the combustion chamber than the engine could burn. Lots of soot came out the hole in your header and got smeared around the engine box and also covered your dingy. This unburned fuel does also get in your crankcase and dilute your oil, not good but not horrible. That is sure death for a gas engine but Diesel is a lubricant, but not a good one. Some diesel engines (boats in my experience) seem to “make oil”, the product of this situation or an injector pump leak…
Next time when you climb hills pull your foot back on the throttle till the black stops and you will find no loss in power. It will be kinder on your dingy, your engine oil, your fuel bill, and the environment. Please note that my dingy is heavily covered in black soot, but I do change my oil rather often.
For what it is worth, Peter |
Scott Whitney (66.82.9.27)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 1:19 pm: | |
Hi Mike,
While I don't have any solid info for you I can sympathize with the experience. I was driving out of SLC in the dark one very cold night and stopped for fuel. I was appalled at how much smoke was coming out my stack and stinking up the place. I had noticed no loss of power and all guages had been reading normal. It was dark so I didn't even see the smoke until I stopped. The funny thing was that none of the truckers even seemed to bat an eyelid about the amount of smoke I was creating in the fuel island (I shut it down ASAP of course.) Apparently this smoke is normal at high alt. for a non turbo engine. (8V71 naturally aspirated)
But I would have thought that a turboed engine would not suffer this rich burn phenomena. But maybe CO is that much higher and even the turbo can't pump enough air in there to lean it out if you are pulling hard on hills?
I do like driving in the daytime for one big reason of monitoring my exhaust color. Pulling hills, I try to give it just enough fuel to climb, but not enough to smoke. I don't mind driving the flats at night cause I can pretty well judge by my speed how rich I am burning. I wish there was a gauge to measure exhaust opacity - maybe an infared camera rigged on the stack would work...
Scott |
Max (210.190.70.242)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 2:08 pm: | |
Scott,
I think an oxygen sensor drilled into your exaust pipe and hooked up to a guage should tell you your air/fuel mixture, no need for a camera. |
Red (141.78.3.230)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 2:53 pm: | |
If you were pulling a hill in high gear at low rpm and now you got a hole in your exaust pipe and oil everywhere you probably melted a piston from excessive heat, a pyrometer would have warned you of problems. Thats an expensive mistake with a late model prevost conversion, ouch!
Im suprised that coach salesmen dont teach people how to drive a diesel before handing them the keys. A diesel is not a short stroke gasoline engine they operate very differently.
You cant drive up a hill in high gear at low rpm because the exaust gas tempreature goes above 1300 degrees at which is the melting point of aluminum pistons. This is probably why you developed a leak in the exaust pipe, it melted. |
Mrbus (205.188.209.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 3:16 pm: | |
Everyone is talking about pulling the hill in high gear, I doubt if the Prevost has a manual transmission, so the Allison would not have stayed in high gear. True enough the gauge you are wishing for has been here for many years, it is the Pyrometer. It simply reads exhaust gas temperatures, by a probe installed into the exhaust and transmits it to a gauge on the dash. Very simple, incredably accurate, and the best engine saver available. At high altitude, even with a turbo, if you keep your foot flat on the floor, you are pouring more fuel into the engine than it can possibly burn, ergo the black smoke.
As Peter stated above, just lift your foot until the temperature drops back to around 950 to 1000 degrees F,on the pyrometer or watch the smoke in the daylight. and you will suffer no loss of power, and save many $ in engine wear and wasted fuel.
If you did not experience any rough running of the engine, I doubt that you melted a piston (could have though) clean the engine compartment, fix the exhaust leak,& learn to drive your engine to get the peak performance. A pyrometer is a great tool for doing just that. In the early days of highly fueled diesel engines, the old cummins 335 was famous for melting, the pyrometer became the instrument to operate by. Aircraft engines, both piston and turbine are operated according to exhaust gas temps., maybe there is a lesson here.
Gus Haag |
John Rigby (24.174.234.92)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 6:42 pm: | |
Gus
Good info,where would you mount the sending unit./piping? manefold? where would you go to purchase a gauge and sending unit?
Thanks
John Rigby |
MRbus (152.163.188.227)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 12, 2003 - 7:52 pm: | |
John,
Several places to mount a pyrometer sending unit, all depending on engine make and model. The standard method of mounting for all applications is to drill the correct size hole in the pipe, install the threaded connector by brazing it into the pipe, the sending unit screws into this fitting. There are two electrical wire connections on the probe, and they are usually protected by a couple of feet of heat resistance wire wrap, just to protect the wire. The pyrometer requires no outside electrical source, simply run the two wires to the dash and attach them to the correct fittings on the back of the gauge. I have found that # 12 wire works best for the long runs needed in a bus.The connections are polarity sensetive, so if it does not read when you start the engine, just reverse the wires.
The best place to install the probe, depends on the enging make and model. For any of the turbo engines,(8V-92T, 6V-92T or 8V-71T) mount the probe in the elbow pipe on the exhaust side of the turbo(toward the muffler). For non turbo, (8V-71,6V-71 or 671) mount the probe in the first pipe after the manifold connection. Technically the V configuerations without a turbo should have a probe mounted on both side exhaust pipes, but this only increases the cost. If using the single probe on a V engine, place the probe on the exhaust pipe on the curb side of the bus. (right side looking from the rear.There is a reason for mounting on this side, but takes a lot more explaining, just use that side and you will be safe. Always mount the probe as close as possible to the turbo, or the exhaust manifold for the best readings.
The most popular manufacture of Pyrometers is "ISSPRO", you can find them at most any heavy truck supply, or the parts department of most truck dealers. If you are a scrounger, try heavy truck salvage yards. Good Luck Gus Haag |
Mike T (66.82.9.13)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 13, 2003 - 1:05 am: | |
Thanks for all of the interest and input. I was watching the pyrometers and they were normal. I was probably too heavy on the pedal some but I was backing off most of the time. It is an Allison which seems to know exactly what to do all of the time. So hopefully I'm not in big trouble. I should have an answer tomorrow when I have it looked at by a trustworthy shop I know here. At least now, thanks to you all, I have some clues to go in there with. I'll let you know. BTW Gus was right. I just meant the high demand of a large dingy and a big hill - not high gear. I think I didn't realize how much of that greasy unburnt fuel is put out until I saw it all messing up the place that my engine lives. I went skiing today and forgot about the whole thing for a while which was good. The parking people told me I can park up there at the mountain with the tour busses! Right next to the hill! I am so stoked! We may not be pulling the toad over the pass. |
FAST FRED (209.26.115.220)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 13, 2003 - 5:51 am: | |
It is possable that some brain stuck a big set of injectors in the engine . This would explain the goo everywhere.
You might read the tag on the side of the injectors & look in Da Book to see if there is a mis match.
FAST FRED |
Mike M (152.163.188.227)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 13, 2003 - 6:47 pm: | |
If you have a Hydraulic fan, it could have blown the seal. Or one of the hoses feeding it.
Makes a big mess with the fan blowing oil all over the place. |
Mike T (66.82.9.14)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, January 14, 2003 - 1:03 am: | |
I have a belt driven fan and miter box fluid is good. I went to the shop today and the pro's say everything looks normal. Case in point for detroit, Johnny. Looks like I am lucky. The exhaust leak was blowing unburnt fuel all around and I am guilty of a heavy foot. They are going to work on it and an air leak tomorrow but they did look at it today. It's running great so I feel relieved. Someone at the RV park today told me he runs his oil at the add mark when checked cold if he's about to do a lot of hill climbing. He says less smoke and cooler running is the result. That sounds scary to me. Any comments? |
jmaxwell (66.42.92.23)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, January 14, 2003 - 3:14 am: | |
I think the add mark translates to 1 gal. low at cold. Running at temp. it would be about 2 qts. lower on the stick. Not enough oil and I suppose that is why they put the "add" mark where they did. I have had a couple of experienced DD mechanics tell me that it should be about 1/8" above the add mark at normal temp, idle, at a minimum. I would think that too low would increase engine temp. and possibly cause injector malfunction, especially on hydraulic injectors. |
Mike T (66.82.9.25)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 16, 2003 - 4:34 pm: | |
Well, it's official. I'm OK. The muffler mounting brackets had broken (apparantly some time ago). The rubber mounts had dried out and let the muffler fall down onto the frame below it and that caused a connection at the first clamp to separate. I had an exhaust leak for a long time that I didn't notice until it was blowing the unburnt fuel. What a mess. I think I'll keep my oil level where we all know it belongs and motor on. Thanks everyone. Mike |