I just replaced the air cleaner on our U300 and thought I would pass on some information and tips.
Since the 6V-92TA is a two cycle diesel, It uses much more air than the other engines found in our Foretravels. Rather than intake valves, the Detroit has big intake ports in the side of the cylinder walls and all four valves in the cylinder head are exhaust valves. Since the Detroit fires each cylinder every time the piston comes up, fresh air is being constantly pushed through the engine by the large Roots supercharger. At full throttle, the turbocharger compresses the air before it gets to the supercharger so even more air goes through the engine. This is the reason the muffler has 5 inch tubing in and out. Also the reason the 2 cycles run a much lower exhaust temperature than 4 cycles. In my opinion, also the reason the U300s have a distinctive "Greyhound Bus Station" smell and remind some of us of bus trips in our past.
With the installation of the side radiator on the 350 hp U300 models, the air intake is in probably the worst possible place, right behind the rear tires where it picks up all the dust and dirt from the road. Since the 2 cycle Detroit is using huge amounts of air, the filter clogs up fairly rapidly and the tell-tale indicator in the engine compartment turns red.
Our tell-tail indicator turned red on our last trip and I ordered a new filter. After installation, we just finished a 460 mile trip and averaged 12.11 mpg at 60 mph top on the freeway. This was mostly at sea level with a decent and climb back to 2400 feet and down to the house. Not too bad. Tank was carefully measured to within an eighth of an inch before and after the trip with the coach dead level.
Buying a new filter:
The list price on a Wix 42610 varies from a low of $124 to $214 (each). Sears wanted $130. After about 30 minutes online, I found one for $37 but they were out of stock. Ebay came through again with a delivered price of $62.99 for the genuine Wix part.
Seller: blackhatauction ( 105448 )
Item title Price
Shipping price
Qty Item total
NOS Wix 42610 Air Filter Element PA-2501/EAF5024/CA-3517/AF-3057/42610 ( 390480298909 )
Paid on Jan-03-13 $62.99 Free 1 $62.99
USPS Parcel Post
Estimated delivery: Mon. Jan. 7 - Mon. Jan. 14
Subtotal $62.99
Total $62.99
Note: filter was shipped from AZ and arrived quickly.
In replacing the filter, use the new gasket in the box and carefully lift the outside end as you put the cover back on. The four black nuts should tighten fairly easily and indicate that the filter has sealed at both ends. The smaller of the two ends has a tiny hole to allow the differential pressure to go through the plastic line to the tell-tale indicator.
The old filter may be taken out and cleaned with a air blow gun but even after over 30 minutes of cleaning, the tale-tale still turned red on a test drive. Trying to clean a wet filter with a blow gun will tear the paper filter material and allow dirt straight into the engine.
Bottom line: The $63 is quickly paid for with increased fuel mileage and more power. On I-80 from Sacramento to the turnoff at Auburn, I passed a dozen big rigs on the upgrade and only shifted down into 3rd once. A big difference from coming home the previous trip.
Pierce
Pierce,
What was your average mpg before the the change? How often do you change it or do you always just wait for the tell-tail indicator to turn red? 12.11 mpg is fantastic! My mpg on the last trip(450 Miles) was around 7.5 on my U300. I'm in the process of doing the maintenance on mine and I will start with the air filter. Just got back the Blackstone lab oil analysis to get a baseline on the engine at 82000 miles. I was not a good report as far as metals and fuel in the oil, or possibly a leaky injector. I still need to test the coolant and the rest of the fluids. I will try and do as much as I can before I take it to Johnson Diesel Home Page (http://www.johnsondiesel.com/) to have it serviced. They are the 2 cycle Detroit experts around here.
Any advice would be greatly appreciated.
Jerry
Jerry,
Because of the terrain here, our mileage varies a lot. On the trip from Santa Barbara to Monterey along highway 1, we got only 5 mpg. From Grass Valley to Reno and back, we are around 7 mpg so it really depends on the elevation changes. I use more fuel on 45 miles of highway 49 up in the Sierras than I do driving to San Francisco. The 12 mpg was w/o toad.
I tried blowing the dirt out with air after the tell-tale goes red but with the price of diesel so high, I think it's less expensive to just install a new one plus the cloud of dust is huge when you try and clean it. With the intake so low, the bottom of the filter canister has leaves and even twigs in it.
I don't run any synthetic in the engine, trans or rear axle but think the following have a lot to do with mileage:
Maximum cold pressure as placarded on the sidewall with no adjustment for temperature. 110 psi in my case.
Keeping speed to around 60 mph. The drag really goes up as the speed increases.
Excessive toe-in can show up in decreased mileage.
Radiator fans stuck on high speed would drop it also.
Exhaust leak between the exhaust port on the cylinder head and the turbo will cut power and mileage. Other members have reported cracked exhaust manifolds.
New tires will drop the mileage from a little to a lot. Do a search on Google for forums that focus on "poor, low fuel mileage with new tires". Some members have reported up to a 25 percent loss. Don't know how long this effect lasts or what it does to large tires like ours.
Make sure the Allison is shifting into direct. Third to fourth shift should be at 48 mph with a light throttle application on flat ground. 2125 rpm will translate to 82 mph with the stock ratio for a 350 hp Detroit. Just work the ratio backwards to figure other speed/mph combinations in fourth direct.
We are only 36 feet long and don't full time so with partial tanks and not too much in the compartments, this has to help.
Search the archives for Bill Chaplin's Excel file. He documented their trip with distance, speed, etc. Nicely done. He recorded excellent mileage on several legs of the trip. His also has a '93 but is 40'.
With a Detroit 2 cycle, the injectors, short return lines are all under the valve covers and not visible from outside the engines. The return lines can leak diesel into the crankcase. Fuel pump might be another possibility but don't have a direct knowledge here. Detroit 2-cycles because of the intake port configuration, will use more oil than a 4 cycle. During a trip, the dip stick should indicate a little lower as the days go by. When checking the oil, smell the dipstick. A diesel smell will be present if any is in the crankcase.
A bad injector can drop mileage. Owners on boat forums complain about mechanics having to bring 8 injectors to service a 6 cylinder DDEC detroit as a couple new ones would be defective. The machine to rebuild them is VERY expensive and not necessarily 100%. They cost several times as much as the mechanical injectors the older engines used.
A trip to Yellowstone only saw 7 mpg w/toad (3000 lbs). Met another 40' U300 owner in the park who averaged 7.9 in five years of traveling with full sized PU toad. Only repair in five years was a cracked exhaust manifold a couple of weeks earlier.
Using a clean tape measure with the rig level and the tape vertical is a fool proof way to figure mileage during a trip. Tape has to be cleaned between dips as the diesel does not evaporate and needs soap and water to remove the shiny diesel. 6 gallons per inch on our tank.
Pierce