Driving a Detroit Diesel xV92

[fulltiming]

Many of the members of this site have either Detroit Diesel 6V92's or 8V92's. These are 2-stroke engines and some of the conventional wisdom about driving a vehicle with a diesel engine does not fully apply to these 2-stroke engines.

I found an article on Tejas Coach Works (http://tejascoach.com/tejasoil.html#Drive) which describes driving techniques for the 2-stroke DD's. Although the article may get a little technical for some, please take the time to read it if you have a 2-stroke DD.

In particular, there are several great take away thoughts from this article:
1) Drive it like you stole it - drive the 2-stroke DD's up on the power curve. Note: Most of the 1980's and early 90's Newells had 2-stroke DD's and were geared to run 1700-1900 rpm at 65-70 mph. This is frequently the sweet spot for a these engines.
2) Never lug a 2-stroke!!!! Lugging is running the engine where it can not accelerate in the current gear given additional throttle. Note: If your foot is on the floor and you are not accelerating, you are lugging the engine. If your foot is not on the floor but pushing harder on the accelerator will not increase ground speed, you are lugging the engine, even if you are at 2100 rpms (redline). The DDEC equipped 2-strokes will try to compensate for lugging but it you are climbing a grade with your foot on the floor and your Newell is losing speed, you need to back off then, when it is safe, downshift. Remember that your engine will increase by 400+ rpms when the automatic transmission downshifts. You will see the coolant temperature start to rise rapidly and frequently the oil pressure starting to drop under these conditions and that can be a death sentence for a 2-stroke DD.
3) Excessive idling is BAD!! Try not to let the engine idle for more than 8 minutes on slow idle. Use the Fast Idle switch if you think you are going to need to idle longer than a couple of minutes. The article points out some really bad things that can result for excessive slow idling (such as run-away engines) that you likely have never considered.

Scrolling up and down the webpage, you will also find hints on starting in hot and cold weather, oil consumption and other interesting areas. Most of the 2-stroke DD Newell's have block heaters. When it is cold outside, use them. I typically turn mine on 4-8 hours before I am going to start the engine if the outside temperature is below 40-45 degrees.

[encantotom]

i had read this article before i bought my newell. i had concerns about a 2 stroke diesel at first, but between this article, me remembering that all the buses i had rode as a kid were 2 strokes and my buddy who had 2 stroke fuel tankers for years it made me understand that they are great engines, as long as you dont overheat them and underdrive them.

i love the sound of my 2 stroke engine much more than the sound of the newer 4 strokes. that doesnt mean i wouldnt love to have a series 60, but that aside, i love my 2 stroke.

since i had a cracked head, i have become more paranoid about heat and have put in a pyrometer and new temp sensors.

lastly, my mechanic also uses the saying, "drive it like you stole it" and said that after i had my new head put on and new cylinder and piston when i asked about a break in period.

thanks for posting it michael,

tom

[Richard and Rhonda]

I also heard the advice " slam your thumb in the door when climbing in, that puts you in the right frame of mind to drive a two stroke"

Michael, good post, it's counterintuitive to rev a diesel.

[encantotom]

if the best way to drive a 2 stroke is after you have injured yourself while working on it, then i have to say i am in good shape......and my engine can rest assured it will be too.

tom

[chockwald]

Wow....Michael, thanks for posting the article......the only thing I haven't been doing wrong is idling too long, but I have not been driving it aggressively enough. OK, Tom, I can hear you thinking...."now he'll drive faster than an old lady".....probably so, now that I know better....LOL!

[Wally Arntzen]

So Tom, it looks like Michael got you to lift it above 65. We broke you in a little on the trip to Austin by going 68, but now, who no's you may kick it up into the75 range.
Thanks Michael for the input, I used to drive mine 75 most of the time on the interstates but slowed it down to 68 to try and reduce fuel consumption.

Wally

[fulltiming]

Remember that the engine isn't the only thing that is involved in speeds above 65 mph. Tires, especially in hot weather, can be more of a deciding factor than the engine, especially since even at 65 mph you are getting the engine up into the range of the sweet spot. Every one should drive within the safe limits of their tires and their comfort level but, when you get a chance within the limits of the tires and road conditions, get a load on that engine.

[zcasa]

Michael, another outstanding post. Thank you very much. I do my best to find out what I should be doing. I downshift regularly on these hills that I travel. I try and keep the rpm's at 1,800 or so. Isn't always easy to keep it there, but I try and watch it. Also, the info on idling is excellent and the engine preheat is very good information. So, now I do not have any idea about a runaway engine? What is that all about?

[fulltiming]

Runaway engines can occur in diesel engines. A diesel engine does not use an electric ignition system. The high compression of the engine causes the fuel to combust without spark plugs. A runaway engine is the result of air and fuel being feed in excess amounts with no way to slow the engine. As long as the blower (not the turbocharger but the roots type blower) is continuing to blow air into the cylinders and diesel (or motor oil) is being feed uncontrolled to the cylinders the engine will run as fast as it can until either something breaks or the air flow is stopped or the supply of diesel or oil is stopped. If there is an oil leak into the air box (the part of the engine on the outside of the head where the air is forced in by the blower) the engine will start feeding on that oil and burning it in addition to any diesel that is being pumped in by the injectors. This could potentially cause a runaway engine. Many of the industrial use DD mechanical 2-strokes were equiped with an emergency shut off flapper that physically closed off the air intake so the engine would starve from lack of air. The likelihood of a runaway engine in a well maintained coach is very small but, as the article points out, excessive idling can cause the buildup of oil in the airbox. The combination of significant amounts of oil in the airbox with the normal flow of diesel could cause a runaway engine.

[77newell]

Any diesel can run away, not just two strokes, if provided with a souce of fuel beyond that need for normal operations. I used to work for a chemical company and was the project leader for a plant site fire water supply system driven by large diesel pumps when a fire situation would occur. Since the plant site utilized flammable liquids that could vaporize if released to the atmosphere we had air cut-offs installed on the engine intakes to prevent run-aways if an engine started ingesting these vapors. Though such a release never happened it was nice to know we wouldn't completely destroy our fire fighting capabilities if it did happen.

If we were to break a propane line and the vapor just happened to make its way to the engine intake on our coaches the engine could conceivably run away. Not likely but it is possible. Any burnable material that could enter the engine cylinders could cause a run-away. Due to the internals it is more likely on two-strokes but it isn't something I stay up late worrying about. I'm more worried about the cost of the fuel I intentionally burn in it.

Jon
1977 Newell 3500

[encantotom]

I am suprised that jim ellis isnt commenting here. he had a runnaway just a few weeks ago and it was a scarey ride according to him....so though not common, it does happen. he has a 8v92 in a 87.

tom

[ABnormal]

Michael to the rescue, once again. Now I have a question.

I live in a cold weather region and each winter I have gone out and purposely run the engine and generator for about 1/2 hour at least once a month. Guess I won't be doing that anymore. Now my question. Michael stated that "The likelihood of a runaway engine in a well maintained coach is very small but, as the article points out, excessive idling can cause the buildup of oil in the airbox.". If there has been a buildup of oil, does it go away with the next road trip or this something that must be cleaned out by a mechanic? I typically run at least 72 on all trips. I will have the coach into Newell next week and if need be, they could clean it up.

And Michael, I am still waiting on that book, "the Newell for Dummies". I will be first in line to buy one.

Thx,

Larry P. in KC

[fulltiming]

Thanks Larry. The issue about running the engine and generator monthly up is a very good one. My recommendation, based on information from most diesel engine manufacturers, is as follows:

1) If practical, every month or so it is advisable to start your diesel engine and then drive your coach for 40 minutes to an hour. This will provide the greatest benefit to the entire coach. If you can not drive the coach to let the engine warm up to normal operating temperature, you are better off not starting the engine at all. Just running the engine at an fast idle does not put a load on it and will not allow it to warm up properly. Running the engine at low idle will result in more damage than benefit, including increasing the potential of oil buildup in the airbox. If you can take the coach for a run, you are benefiting the engine, the transmission, the air system, the brakes, the tires, etc. One of the reasons that over the road trucks get longer life out of their engines than RVs is that they don't sit without being started for months at a time. This advice applies to ANY diesel powered coach, not just Detroit 2-strokes. Now to the issue of cold weather starting specifically. If you keep you coach in a heated building, the issue is irrelevant since above 40-45 degrees the engine should start well with decent batteries and after allowing a couple of minutes to allow the air pressure to reach 120+ psi, you are ready to start driving the coach slowly at first to let it warm up. When the engine temperature reach normal, then you are ready to 'drive it like you stole it'. If the coach is kept outside in very cold weather and at least 15 amp electricity is available, turn on the block heater (nothing else including the battery charger unless you want to trip the breaker) 4-8 hours in advance to avoid additional engine wear at start up. But, you ask, what if the coach is stored outdoors in very cool temperature and no power is available to the site? I would wait for a warmer day to try to start the coach. A coach with a Primus or Aqua-Hot system is capable of warming up the main coach engine much faster than an electric block heater so you may have time to fire up the Aqua-Hot or Primus unit on diesel/propane and let it run with the engine preheat on for an hour or so to warm the engine before taking it for a winter spin. If there is ice on the roads, wait for a decent day.

2) Running the Generator. The generator most commonly used with the diesel powered Newells are powered by diesel engines also. Here there is an interesting difference. The small diesel engines that power most of our generators are equiped with glow plugs to help them fire up in colder weather. Generator manufacturers recommend that the generator be run for at least an hour a month under load. Accomplishing this is much easier than warming up the coach's main engine. First, you don't need to go anywhere, unless you are in a warm building where the exhaust fumes from the generator might be a health issue. Use your glow plugs to pre-heat the combustion area (typically 30-45 seconds, read your owners manual for specifics since many different diesel engines have been used in gensets over the years). Fire up the generator and as soon as the the generator is running smoothly, start loading the generator by turning on electrial devices one at a time. If you have an Aqua-Hot, you can fire up the Aqua-Hot on electricity and put a nice 240 volt load on your system. If you don't have Aqua-Hot you can turn on your electric heaters in the coach to put a load on the genset. If possible put a load of approximately 50% of the rated capacity of the genset on the generator during the time the generator is running. When it is time to put the generator back to sleep, turn the electric loads off one at a time to give the generator time to adapt to the reduced loads, then let it run for a couple of minutes with a very light load, then shut it down. Of course, if you are taking the coach for a nice drive, you can accomplish both at the same time.

3) Now to your second question regarding oil in the air box. If you do not have excessive idling, it is doubtful that you will have much oil in the air box. DD 2-strokes have air box drains with check valves in them. Under low pressure, such as generated at low idle, these valves open and allow oil to flow out of the heads, typcially into a drain canister. At higher pressures, typically above 800-900 rpms, these valves close. The air box drain canister should be emptied at least annually. There should be a petcock on the bottom of the canister. If there is almost a full canister of oilly mess in the canister it has either been a LONG time since it was drained or you have a potential problem that needs attention. For those who haven't seen this canister, it is located on the driver's side of the coach, along side the engine/transmission near back of the rear most tire. It looks like a black fuel filter with a petcock on the bottom and has a pair of small (~1/4") tubes on the top that run up to the sides of the cylinder heads. Draining this canister likely saved Tom from destroying his engine when he found it full of coolant indicating a major problem. If you don't feel comfortable draining this canister, most truck repair shops and certainly Newell will be happy to drain it for you. Remember that in cold weather, it will take a while for the thick oilly substance (it also has some diesel fuel residue in it) to drain out.

If you are regularly draining the air box drain canister and not finding excessive amounts of oil in the canister, you are unlikely to find much oil in the air boxes. If you want to be sure, there are small air box inspection ports on the sides of the cylinder heads that can be opened to view inside the air boxes (each cylinder head has an air box). These look like little rectangular boxes screwed onto the side of the cylinder head above the exhaust manifold. Remove these inspection ports when the engine is shut down.

[Wally Arntzen]

Michael, you are right on with the cold weather information.
I have slept in my coach in 20 below zero temperture at a Green Bay football game and my generator started with no problem using the glow plug.
There is no doubt that my coach engine will not start in temperatures below 40. With the generator running and the engine heater on mine will start very easy after about 2 hours.
My coach is probably one of the most used in extremly cold temperaturs and it is not a problem if you think about what you are doing.
In september of each year the guy who works on my coach in minnesota puts a quart of alcohol in all my air tanks because I did have a brake line freeze up in santa fe about 5 years ago.
Most of the time when sleeping at night in a Wallmart or rest area I leave my generator all night long, to keep heat in my lower water compartment bay.
Wally

[chockwald]

Michael, and Wally.....wonderful information. I'll be checking my airbox drain cannister.

[jdaniel]

I saw the 2100 rpm redline mentioned here. I many times travel at 75 mph which is close to 2000. Is that a problem?

[encantotom]

2000 rpm is not a problem. that said, 75mph is at the limit of what the tires are rated at. if you tow a car, some have limits on towing below that as well. my 2008 honda crv limits to 65mph.

though it is always good to get places fast, i must admit, i enjoy driving at 65-68mph more than 75mph and i have done both for long periods of time.

thanks for posting!

tom

[chockwald]

Michael and Tom, I cannot figure out where my airbox drain cannister is. I have looked on the driver side of the 6V and cannot locate anything resembling a cannister. I found what looks like a vacume resevoir, but no cannister. Do I have to get under the coach to find this cannister? I can see the large oil filter down below, and I can locate the two fuel filters, but no cannister.

[encantotom]

it is only visable from underneath on mine. not from the top. there is a steel canister about 6" in diameter and maybe 10" high and on mine is on the drivers side about a couple of feet towards the front of the bus in front of the engine. it has a drain petcock on the bottom. it has two lines going into it and one comes from each side of the engine.

to drain mine, i would have to get underneath the bus or have long arms to reach underneath....

tom

[fulltiming]

Describe the vacuum reservoir you found. If it is a black canister looking like a fuel filter, that might be it.

[chockwald]

OK, found the air box drain canister....was located on the right side just in front of the rear wheels. Got a 2 gallon bucket, and was hoping I wouldn't need all of it, however, the canister looks like it holds 1 gallon if full. I got 1 quart....I thought it was more when I was talking to Tom on the phone, but I was holding the bucket up to the pet cock valve so the wind wouldn't blow the oil on me...was going on how heavy it felt...so much for my estimtation skills. Not too bad for 14 months, and who knows how long before I bought the coach it had been drained. Anyway, no coolant, or any other foreign fluids....just thick, black, old oil.

Here's a picture of my canister....

[Brian Long]

Great Information and photo. Did you have to raise the coach or use ramps to get under the coach? I want to do this procedure as I have been following the threads and want to make sure I do not have water in the cannister.
Brian
87 37' Newell Classic

[chockwald]

Just left it at ride height, and blocked the rear so it wouldn't fall on me, and crawled under....plenty of room. I have to say that without encouragement from Tom, Richard and Michael, who seem to be fearless when it comes to taking care of this important maintenance stuff I would be reluctant to try it myself. When Tom found coolant in his canister it put the fear in me to take care of this simple procedure. This is how you avoid major engine failure...take care of the small stuff, be proactive, find the problems when they are small, and affordable. I know it cost Tom several thousand dollars to fix his problem, but had he not done the routine checking it would have cost $10-15,000 when he suffered catestrophic engine failure, maybe on the trip he took to Texas recently.

[zcasa]

Just had my service done yesterday, for oil, filters etc. and they drained the air/water seperation tank. It had a self drainer on it, but it had corroded and no longer functioned, so we had to, for now, put a new pitcock drain valve on it. I didn't know that they made self draining ones. I think I'll find out if they are available in the marketplace, because it seems like that would be a good idea to have any water draining out immediately. The other easy choice that I have seen is that a cable can be installed which, when pulled from the side of the Coach, will drain the tank without having to get under the Coach. One of our guys at the mini-rally, Pete, had such a system on his 95 Coach and it sure seemed convenient. I found a freightliner shop that said you can buy the setup for $24 each, plus labor if necessary.