| Author | Message | ||
| 8V-71 (205.188.116.135) Rating: N/A |
My old 8V-71 seems to have less power these days, runs a little colder (165-175) and spits a bunch of oil & fuel on the back of my bus, and I do mean a bunch! Seems to run well overall, uses very little, if any oil, but does drop a little oil on the ground. Fuel mileage is not great 4 to 5 (maybe less sometimes) and the power on steep grades is limited (the bus slows down to about 30mph or even less on 5% grades). Some white smoke on start up and a little but not all that much black smoke on heavy acceleration. The engine overall runs great and just completed a couple long 2000+ plus mile trips with no issues, yet I sense some problem is looming. Any ideas? | ||
| Jayajy (64.12.116.135) Rating: N/A |
Look for a cracked exhaust manifold, or loose manifold bolts/nuts. When was the last time you changed the fuel filters? Is the air filtration system partially clogged? Check the E-Stop flapper above the blower, and be sure it is wide open. Make your wife push harder/faster on long steep grades. That's about all I can come up with at this time. Perhaps more later. Cheers...JJ | ||
| John Rigby (24.174.238.253)
Rating: N/A |
My 671 had a loss of power. It was a bad fuel line sucking air and a wrong connection on the head to hose return line back to the tank. John Also like jj said fuel filters, air filters and the emergency stop not being set correctly. | ||
| jimmci9 (209.240.205.60) Rating: N/A |
sounds like a tune up, setting injectors, valves and governor is in order.... also check to see its getting the necessary no-load hi idle setting necessary for your application...somewhere around 2250 rpm... | ||
| BrianMCI96A3 (69.34.169.50) Rating: N/A |
If it is using no oil... it's not spewing oil, it's spewing unburned fuel. ...And since it is spewing a lot, I'd have to think clogged injectors. A bad spray pattern won't burn effectively, and the worse it is the worse the burn will be. The worse the burn the more fuel will pass out the tail pipe and onto your bus AND the less power you will have on hills. Brian | ||
| gillig-dan (192.89.97.1) Rating: N/A |
to JJ's message above... what effects would a loose exhaust manifold have. I am not burning all my fuel since the engine was put in last week (black smoke). I haven't had time to check much yet but, I know the shop that installed the engine did not bolt up my exhaust down pipe properly and it is leaking. Would a colder than normal engine (150 - 160 degF) cause black smoke? I haven't changed my thermostats after the engine rebuild. I think I should have more power also. Gillig-Dan '70 Gillig 636 Cat 1160/3208 | ||
| steve souza (Stevebnut) (24.60.226.230)
Rating: N/A |
my 6v71 seemed to gain lots of power from an air filter change even though the old one looked clean. I would try that first. They are kinda cheap at around forty sumthin bucks. Though yours soounds a bit more serious than just a filter. A good tune up may be in order. If your mechanicaly inclined get yourself a tune up kit and a detroit manual and tune away. It was not that difficult even for me and the results will surprise you. Steve | ||
| Stan (68.150.152.113) Rating: N/A |
Setting the rack on a DD inline is quite simple but a V engine is more art than science. It takes a lot of practice to get both banks to pull equal load. | ||
| Jayjay (64.12.116.135) Rating: N/A |
Loose exhaust mainifold bolts/cracked manifold causes the head to run cooler, especially important on a two stroke DD. It can also affect the mixture, due to a difference in fuel/air mixture flow/swirl charactistics, which can also be affected in part, by the cylinder back pressure. 150 deg. F is far too cool to efficiently burn the fuel charge (which may not be correct anyway-see above) One (or both) thermostats may be stuck open, since you should be at around 185 deg.F. Lay hands on an infrared remote read thermometer and check the temperature of the thermostat housing. This is also a good way to see if your temp guage is accurate. You say you don't have a digital, infrared thermometer? You better get one, 'cuz they're indispensible (and cheap nowadays) Tires, brakes, wheel bearings, thermostats, oil lines, genset area hotspots, clogged A/C condenser core/ partially blocked radiators, the pot roast for dinner...all are in need of checking for safety purposes. Good luck, and let us know what the final disposition is. Cheers...JJ | ||
| Gillig-Dan (63.111.68.130) Rating: N/A |
Thanks JJ, I don't know if you helped "8V-71" or not but you sure helped me. I'll replace my t'stats this weekend and fix my loose down-pipe. I just got the bus back last weekend after three months of having the engine and injector rebuilt. The engine suffered a meltdown, probably from cylinders that were running too lean. It seemed to me that I should get the engine running at the correct temperature before looking for other issues that could cause the lack of power and smokey exhaust. I suspected bad thermostats could be the cause but I couldn't find any information on the internet to back up my theory. If you are correct, that would make you and this site the ultimate authority on diesel engines! The IR thermometer sounds like a great idea. If it could be used to measure the temperature of the cylinder right at the exhaust manifold input, that would be a better way to see if a cylinder is firing than messing with the fuel lines, risking damage to them. Thanks for all the help so far, Gillig-Dan '70 Gillig 636 Cat 1160/3208 | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
8V-71, I noticed that you said "my old 8V-71" when you asked your question. I don't know why no one else mentioned it, but you can get most, if not all, of those symptoms from engine wear and broken rings in these 2 cycle engines. It seems to me that anybody who would tune up your engine would want to check on the wear in the engine before he proceded with the tune up itself. The low fuel mileage and poor power at the same time would sure have me wanting to check this out. We used to run two dump trucks the same size, one with a worn 8V-71T and one with a Cummins 335. The fuel consumption of the Detroit was just twice that of the Cummins and the Detroit had little more than half the hill climbing ability. If a rebuild is in order, any other problems should be dealt with at the same time. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher | ||
| Peter Cohen
Rating: N/A |
Can anyone tell me what the normal operating oil pressure for a naturally aspirated V8-92 Detroit should be. On cold start up I have 55 to 60 lbs at idling. When warm I have around 15 lbs at idle ( 650 )revs. At 1200RPM I have around 30lbs and from then onwards up to around 1800 RPM I get 42lbs. Is this safe working pressure.? Would really appreciate an email reply. | ||
| Ron Walker (Prevost82)
Rating: N/A |
Hi Peter ...that's about what they put out for oil pressure.. I've seen themas low as 8 lbs at a idle..Detroit's weren't known for great oil pressure. Ron | ||
| H3 (Ace)
Rating: N/A |
Peter your oil pressure sounds about like mine. I will admit when I purchased the coach, it had 15w-40 and being in hot Florida the oil pressure was scary at times but since changing over to straight 40w the oil pressure is stable just about as you described! I don't think you have anything to worry about! Ace | ||
| Bob Oakman (Bobsbus)
Rating: N/A |
My 8V-71 was recently rebuilt. It has real low oil pressure on idol too. It worries me sometimes. I never let it idol long. Even if it's a long red light, I'll kick the RPMs up a bit to help the oil pressure out... a habit I picked up with my first car, a 1952 Desoto. It had NO oil pressure when idling.  When I start my 8V I get a substantial amount of white smoke. It smells like pure, unburned fuel. It only lasts a few seconds. Is that bad? The rest of the time there is no visible smoke at all. | ||
| FAST FRED Rating: N/A |
As an engine ages (about 100,000 miles)the ability to have really great compression cold ,( with the cylinders out of normal hot shape )begins to fade. A few secomnds is no hassle, many great running engines won't stop cold smoking till 120F or even 140F is reached. Yet will still have 100,000 to 150,000 good miles left in them. In a campsite , if you dont want to stink up the area , just leave the block heater on all night, air up with a 120v comprerssor, and drive pout one min after engine start. FAST FRED | ||
| Abajaba Rating: N/A |
Bob, The white smoke that you say smells like unburned diesel is exactly that. It isn't smoke at all but vaporized diesel that didn't burn in the cylinder because it didn't get hot enought to light off. | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
Bob, some of that unburned fuel winds up in the crankcase, so you want to minimize it, if you can. You said that your engine has been recently rebuilt, but you did not say that it was a turbocharged model. Unless it is below 40 degrees, I wouldn't think that you should see much white smoke IF it is fully broken in. We bebuilt a low compression 6N71 a few years back and were surprised that it was hard to start and wanted to white smoke quite a bit. And it misfired at higher RPM occaisionally. I did some checking and was asked if the engine had spent at least four hours running wide open throttle wight after it was rebuilt. I had to admit that it didn't get that type of break-in. I was also told that if it wasn't broken in, that rings would never seat. After that, I ran it at governed speed for a while with no load. That got rid of the misfiring. Then, I ran it at full load for about four hours. That made a heck of a difference, but I still didn't feel that it was fully broken in. So I went back to the rebuilders to see what they thought, and they said that the four hours might be only the beginning of the break in for some of the harder rings. The low compression(18:1) probably accounted for the rest of the difference. The longer that Detroit ran, the better it got, so I finally quit worrying about it. Did you ever run yours hard and have you run it hard enough? If it won't come out of it, then I would be concerned, too. We have found that even one hour with a 1500 watt engine heater will help a lot, so we ordinarily would not leave one run all night. But they do make lower powered ones, so you might want to make sure about the power. I hope some of this helps. Tom Caffrey PD4106-2576 Suncatcher | ||
| Bob Oakman (Bobsbus)
Rating: N/A |
Thanks for the replies guys! I'm a little cloudy today after the CMAs and after-party festivities. Great night, but long and a wee bit drunken... In my younger days I overhauled a few engines, none diesel. I am surprised how few traits gas & diesel engines have in common.... besides pistons, crank and the like, of course. It does smoke a lot less at start-up on warmer days. It really puffed on those below-zero days when we were in MN. It is turbocharged. I have about 40,000 on the rebuild now. It was broke in making the trip from AZ to Portland, where I took ownership. The guy that drove it up was a retired bus driver. I am hoping that he knew how to treat a fresh rebuilt Detroit. It does run perfect. The only unsettling symptom is the smoke at startup. As far as rpms, she does have a happy place. I don't have a tachometer, but always listen and feel the engine when traveling. There is a certain rpm, around 64 mph, just past the point where the turbo quits whistling, when it smoothes out and gets quiet and more powerful. At 70 it starts to sound labored again. I always try to find that "sweet spot" when driving any distance. Ya' know, when I raised the roof it sat for over a month without ever being turned over. When the time came to back it out of the garage to get the new caps on, I swear it started before it even made a full revolution. I was so pleased. | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
Bob, it just sounds like a cold engine that was designed with low compression for the turbo. They're gonna smoke when you start them below zero. If I start a cold engine, I try to keep the RPM as low as possible without stalling the engine. There is plenty of oil pressure and this seems to build chamber heat quickly with a minimum of banging(knocking) from delay of ignition. This minimizes the smoke before it is firing on all cylinders. That hard fuel knock when cold is hard on things. Adding heat is the best thing you can do to get results. Good luck. Tom Caffrey PD4106-2576 Suncatcher |