Just got back from a trip to Antonito CO which included a long run through west Texas and then climbing Raton Pass. Tempt gauge showed 225 at one point running flat but slowly climbing towards Dumas TX in 100 F and towing pickup. Next morning it started running hot up Raton Pass. Sometimes it runs fine around 185 to 200 then starts climbing up to 210 or 215 for no apparent reason (same speed, conditions. On the way home ran hot up the pass, but then settled down to 195/200 and below for rest of trip. No alarms went off and I climbed at a reasonable speed manually shifting down to keep water pump speed up a bit, no lugging.
Last summer changed out thermostat with Cummins 195 degree thermostat, flushed radiator as per Wolfe and switched over to Cummins Fleetguard OAT coolant. Fresh oil change, new fuel filters right before trip to Colorado. I'm wondering if my fans are going into low speed instead of high sometimes and then back up to high. How does one test the fan operation is my first question? I've checked radiator for obstructions, dirt, and there was no loss of coolant except for changing out the coolant filter before the trip. I use a blank coolant filter.
If I can't figure this out, would it best to start at MOT or FOT to make sure fans are working properly? I've got a small film of oil on both fan motors and below hydraulic pump, but no change in fluid level in the reservoir tank over 12,000 miles since filter change in 2017. My home is sold and we have to be out of it by end of month. In November we hope to be full time on the road when wife retires. This has got to be resolved by November.
You'll need to locate the device that controls your fan speed. Search the Forum for pertinent threads that may help point you in the right direction. Once you have found the speed controller, you can fiddle with it.
If it is one of those wax capsule controller valves, I'm not sure how you would make it change speeds to see if both modes are working. I'm not familiar with those devices.
If it is a electric solenoid valve, turning the power to it on and off should cause it to change speeds.
If you can't tell what the fans are doing by sound alone, you could pick up a non contact tachometer to check the actual RPMs. I bought one at Harbor Freight several years ago. Probably sell them at Lowes or HD also. Example below:
https://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html
Mine has the wax capsule fan controller, no electrical connection.
Factory fan control on ours turned the fan on high as soon as the motor warmed up. Replaced with the same controller as source engineering in Oregon sells. 50hp loss on high if not needed. Full speed at 185 vs 199. Better mpg. Better power
Bob, was/is yours the wax controller or the Saider one like mine as I seem to remember if it is turned off it jumps to high speed. I think you said disconnecting it will activate high
John h
Piloted wax capsule. Variable speed. Low to 170. Ramp up to full speed at 185.
Replacement industry wide used is low to 185. Ramp up to full speed at 199 degrees
When it was running hot were you on the top half of your fuel tank,that could make a difference also,my advice would be to check the fan speeds like the above says,that may not be the problem.have you ever had the fuel pump return valve spring replaced or
reworked,many of us has had done or done it ourselves.
195 thermostat? Shouldn't it be a 180?
Here is my valve
On top half of fuel tank.
I would think that a 180 thermostat would be a better choice but that would not address the overheating problem. You encounter the heating even going over Raton Pass. I looked up the elevation and it's just over 7,800 feet. If the ambient was high, the density altitude (the altitude your engine, radiator fan, radiator thinks it's at) could easily have been 10,000 feet. Your radiator fan, intercooler, radiator are much less efficient at this altitude and especially with a mechanical engine, the injection pump does not do a good job reducing the amount of fuel injected so your EGTs soar. Bottom line is your cooling system can't do the job heading up a grade at high altitude, especially in summer weather.
So, you need to downshift to keep the RPM up toward the top of the normal limits rather than trying to pull a grade in a lower gear and if it still is hot, slow more and if necessary downshift another gear. The coolant circulates best at high RPM and the EGTs will be less. Remember, the damage from excessive EGTs is cumulative so may catch up with the engine even years later.
Probably nothing wrong with your cooling system but you got caught out with a combination of high altitude, high temperature and a cooling system that can't keep up. This has killed hundreds of pilots, counting on a normal length takeoff run and don't have the power or wing to overcome the conditions. Plus, many are overloaded.
Our Detroit is the same. Grades that I can charge up in three seasons, cause a drastic slowdown and gear dropping in summer.
Pierce
I put in the one listed in cummins, thermostat 3913028. (Found old thermostat: 180 degree). Yes, high altitude with mechanical engine is more of a challenge for sure. Generator was a little slow to start the first time at the campground when my two-year-old granddaughter turned it on.
The temps posted seem very normal. My dash gauge is almost 10 degrees higher than the engines computer shows on TPMS
Have been helping another RVer with his overheat issue.
You can eliminate the fan motor hydraulic controller as an issue with these two steps.
Take the lines off the wax valve and cap both lines and see if the fan runs wide open.
Then put a union on the 2 lines and see if the fan runs at low speed.
If the above works, would suspect the wax valve is the issue.
Towing a pickup, high altitude thin air, high ambient, high density altitude as Pierce says all play a part. Driving technique is critical, these conditions will reveal any system weakness when running full output. Keeping revs up is important, but there's always the option to drop another gear, lose a few mph, take some load off powerplant/cooling.
We pulled a horse trailer filled with household goods to Ohio with our RAV4 several years ago. My 4107 Greyhound with rear side radiator has also been on long trips. Neither vehicle ever moved the temp gauge off the thermostat in hot weather. With the fore/aft drivetrain setup in most diesel pushers, there is no way to use a PTO like GM did 80 years ago. Good idea then and now too. The idea of the complex system we have is beyond my comprehension. Foretravel realized they had a problem after the side radiator U300 in 1992 didn't make it so they added another motor/fan. It's still marginal in the mountains here in the West in summertime. Not only is the radiator too small but it uses lots of horsepower and creates more heat doing it. In the case of the GV series, there was so much room up front, radiators could have been installed here and taken advantage of ram air also. Porsche, VW Vanagon, etc have done just that very successfully.
If I were buying an expensive RV, I have to say I would be looking at the front engine Freightliner Cascadia RV. Bet the temp gauge does not move on grades and it gets better fuel mileage than our coaches.
Pierce
Foretravel over cooled original U280's and made up a kit to block part of the rear radiator
Sorry you have seen high heat on Raton.
Raton Pass for our coach pulling 5,500 lb Jeep Grand in warm weather is 30mph 3rd gear with light steady throttle. We also keep pyrometer EGT below 950 degrees, and coolant stays below 190 degrees. If needed, we have had some 20mph climbs at 2nd gear for some steep slow drives. Never can go too slow for these few moments of driving. Keeping Tachometer below 1,800 is also a guide on these climbs. We used to overheat approaching 210 when not paying attention to RPM, EGT, no more once we learned to be light on throttle. Every push on the throttle that does not move tach, just puts more fuel into the system, increasing heat gain, without any benefit.
I was in 4th gear with more throttle and speed. Thanks for sharing your experience.
That last sentence in Barry's post is critical for mountain driving. If you are not able to accelerate in a given gear with more fuel, drop a gear manually.
Barry, Wolfe & Amos, just curious if you perform that manual down-shift under full load or if you back off the throttle before making the shift?
Larry
I just punch the button regardless of throttle position.
P
This had to be in the dead of winter to keep coolant circulating while not introducing cold coolant into the warm engine. I had a Volvo with a canvas blind in front of the radiator that pulled up with a small chain. I've seen big rigs with movable louvers for winter driving. In normal weather, how can you over cool an engine if the thermostat is working? Certainly not applicable this time of year.
Pierce
Cats never fully warmed up was what I heard. When where and why I have no idea. Sheet of plywood
Larry,
Transmission will generally take care of itself, but better to not manually shift up or down under hard throttle. So, the better answer is let up a little when the transmission is going to shift.
If Allison wants to automatically shift down, under hard throttle that needed shift may be delayed for a while.
All shifts under hard throttle may be a bit harder on the tranny, but necessary during some situations.
Thanks, Barry. I appreciate your input - a lot.
Larry
Not sure this has any validity. Every time the transmission is in D and downshifts as you slow down on a grade, throttle wide open, it shifts at full throttle. It was designed to do this.
But the transmission is designed to shift under full throttle-- both up and down shifting. Does this on most all shifts as one accelerates and as one looses speed on a grade.
Can you let off to manually downshift-- certainly. But, don't feel you have to.
Don't know if everyone knows this but when you go from drive to nuetral and then to reverse it's alot less bumpy then going from
drive to reverse.
Manual recommends going to neutral between r and d.
Barry may not drive his coach as hard as some of us hooligans. I remember he once stated during a Forum discussion that he never used full throttle. At the time, I did not think he was speaking literally, but perhaps I was wrong.
I can say this: If it was gonna hurt the Allison to shift under full throttle, then the tranny in our coach woulda died long ago. Probably 90% of the time when I'm starting out from a stop I have the pedal to the metal. I love hearing that old Cummins winding out and the turbo whistling. Our coach shifts very smoothly under that full throttle "abuse" - without watching the tach I would often miss the upper gear changes completely.
Starting from a stop is 90% of the time at full throttle. The only time I'm not is in a town looking around. Agree, drive with the window open and listen to the music. It hammers the 1st to 2nd shift pretty firmly but the same at partial throttle. We had Allisons on three of our trucks and all of the small Mercedes 309D buses the city used had them. The buses shifted so hard that it chipped teeth off the ring gear in the rear end. A friend drove one of the buses and had several passengers ask if she was just learning to drive.
Like I said earlier, the HT746 is a garbage truck transmission, just about impossible to hurt.
Pierce
Pierce : I like you, stand on it from a standing start. Want to get that turbo spooled up because I know the supercharger sitting below is hungry for cubic feet of air. What does happen is when it shifts to second I swear it sounds like I "chirp" the tires. Coach came this way and shifting hard like that has not seemed to have hurt it. Just wondering if anyone else ( especially you Detroit diesel folks ) have encountered this
Guys, I ease into mine unless am entering the freeway and it does the same hard shift into second, not crazy hard but not as smooth as second to third. I guess it's the nature of the beast. ^.^d :))
We are assuming it's a figure of speech calling the engine a supercharger.
John,
The Detroit 6V92 has a supercharger/blower not a figure of speech.
Mike
I've never started from a complete stop with full accelerator, but climbing mountains at full fuel I don't risk losing momentum by easing off the fuel when downshifting. I guess it's just me.
When in cruise and the engine shifts down it is with full throttle so I wouldn't worry about it.
Learned something new about the Detroit.
I learn something new almost every time I visit the Forum! I found the image below online. Shows the turbo + blower on a Detroit.
Are the Detroit engines in Foretravel coaches are set up the same way - with turbo sitting on top of engine? Just curious.
Steve,
You have a different transmission but ours makes a fairly hard shift from 1st to 2nd. Smoke reduction is turned on in our ECU so it's dog slow across the intersection, mostly because of the tall first gear in the 4 speed. I tried to turn it off but my Pro-Link does not have a late enough cartridge. You can install a resistor at the boost sensor and it will start fueling right away instead of waiting for boost to build. Here is the fix: BNO BBS - BNO's Bulletin Board System: DDEC - engine slow accelleration (http://www.busnut.com/bbs/messages/233/14052.html)
Detroit 2 cycles have a roots blower/supercharger to give positive pressure to the intake system or they will not start or run. The Detroit 2-cycle uses a massive amount of air while running, partly because it fires on every revolution and partly to push the exhaust out the 4 exhaust valves (no intake valves). This is why the air cleaner must be kept in good condition and especially since Foretravel installed the air intake in the worst possible place the U300 until sometime in 1993. The Roots blower is also the reason it comes with a 5 inch exhaust pipe. Since it runs much lower EGTs, it produces different compounds compared to a 4 cycle so has the distinctive Greyhound Bus Station smell to the exhaust.
The blower is also known as a supercharger as it is mounted on dragsters to super pressurize the intake air and enable the engine to produce lots of horsepower.
If you power your boat/yacht with your Detroit (or Cummins), you can legally turn up the horsepower with this little device. Don't think it will make it a 620 hp 6V-92 but interesting. Detroit Diesel 6V92 MAGNUM EVO-Tech Heavy Duty Performance Chip (https://www.magnumtuning.com/en/detail/evo-tech-heavy-duty-performance-chip/detroit-diesel/6v92)
Since the 6V-92TA is in a "V" configuration, the Roots blower sits in the middle of the V with the turbo mounted on top of that. Some boats or buses install two turbos on the engine at the end, not necessarily to gain more horsepower, but to get the hp at lower RPMs to pop the boat up out of the water or in a bus with a 4 speed, get more low end off the line. Big turbos have more mass in the turbine wheel so take longer to spool up. At high turbo pressures, there is a valve so the turbo boost bypasses the Roots blower. This helps the efficiency.
Detroits have an aftercooler installed below the blower compared to an intercooler (CAC) on a Cummins. It's liquid cooled so can be smaller to achieve the same efficiency. Our Detroit does not have a waste gate on the turbo so the boost starts dropping when you leave sea level. The big reason it needs more fuel off the line at high altitudes.
For those interested, they do make liquid cooled intercoolers and liquid cooled turbochargers. Also, electrical powered turbos to give boost to start 2 cycles if they don't have a mechanical blower.
Pierce
Should have added that Roots blowers/superchargers are positive displacement while turbo chargers are centrifugal. Centrifugal pumps are totally useless turning slowly while positive displacement are effective as soon as they start turning.
Pierce
Truth be told our Cats Cummins and Detroit's will take a lot more hammering than we put them thru.. I've put them all thru it in my Diesel trucks and with service 9out of 10 of them went past a million miles.. Allison Transmission just as durable.
Chuck : Yes It looks just like the picture.
Update! After receiving a PM from a forum member about a similar problem that turned out to be an errant gauge reading, here is what I have discovered. After purchasing a Harbor Freight non contact photo tachometer I measured the radiator coolant fan shaft speed at idle before traveling. My reading was 1032 rpm at the shaft. The HF laser tach is very marginal, working distance 2 - 8 inches, which in this situation puts the tach very close to the moving fans. Let me just say when the D2 hits the air pressure cut off, you need nerves of steel not to jump like a rabbit.
Went for a test drive today in 95 degree weather for about 60 miles. At the 45 mile mark the temperature had started to climb from 180/185 to around 195. Pulled over and tried to measure fan speed, still on low. But it was so difficult to get a measurement not sure tach was giving me a good reading, but seemed to still be on low speed. Measured the temperature at the thermostat housing with IR thermometer and it was 178, same for the housing to the coolant filter. Shot the temperature on the fan control valves (wax valves) and it was closer to 148. Shot the temperature multiple times. Went into driver seat, rapped on the gauge (as suggest by a forum member and it immediately fell to slightly below 180 and stayed there for the remainder of my test drive.
Has anyone replace the gauge? How involved is that job?
Assume it is easy to replace VDO gauge, but first check the wire connections on back since your rap made a change. Remove & replace wires.
For the rad fan high temp hydraulic control, we put a ball valve on one of the small diameter control lines that we can manually close off to test or force fans into high speed. Though have hardly ever used the ball valve since our coach now stays close to 180 on coolant gauge with our more careful, lighter throttle, hill climbing down shifting, especially in hot weather.
My engine(94 model Cat 3116) temp gauge works very good. So much so, that if going up hill the temp is also going up and going down hill temp is going down. On flat level ground running 60 MPH towing with temps above 80 deg. and high speed fans(running about 700rpm slow) my engine temp will be running 195-198 deg., start up any incline and temp will start rising to 200 deg., but back on level or down grade engine temp will start going down slowly. I have a slow fan speed problem that I am trying to fix by replacing original PS pump tomorrow. Also I have noticed and I ignore that if I turn on the dash a/c fan the engine temp gauge will rise by 10 deg. or more and return if I turn the a/c fan back off.
I notice when I turn on my headlights I get more fuel, more temp and less oil pressure. I'm sure there is a connection somewhere that needs attention...perhaps you are getting the same result from the amp draw of the A/C fan??
I should say voltage drop
Jet Doc, about all these old Foretravel's do that. My temp goes up 10 degrees oil pressure goes down 10 lbs. on the dash gauge. It doesn't do that on the SilverLeaf.
Poorer grounds. Frame grounds versus decicated green ground wires.
Supercharged is a physical condition, that is, air is delivered to the cylinder at a pressure above ambient.
The blower on a 2-cycle Detroit supplies scavenging air to replace the intake stroke. The turbo supplies the supercharging. A blower on a 4-stroke engine can function as a supercharger.
Supercharging: A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do more work, thus increasing power.
The Roots blower/supercharger on the Detroit 6V-92TA is a positive displacement compressor/pump. A turbocharger is a centrifugal compressor/pump. Turbos may be installed in pairs in parallel or series and can take advantage of the additional pressure when mounted in series (compound turbo) Unlike a positive displacement, they must be spinning quite fast to increase the pressure.
Fire trucks use centrifugal pumps for their main water pumps. Off road fire trucks may have PTO positive displacement pumps to enable them to pump water while moving a slow speeds.
The 6V-92TA has a valve so once the boost pressure is high enough, it bypasses the Roots blower and the boost goes directly to the engine.
Instead of an intercooler (CAC), the Detroit has an aftercooler mounted UNDER the Roots blower to cool the incoming air charge. It is liquid cooled from the engine's cooling system. The cooler the engine coolant is, the cooler and denser the incoming air to the engine will be. Some CATs have aftercoolers.
Turbos may also be liquid cooled. Liquid cooling is always more efficient than air cooling so the cooler may be much smaller in size.
A look at the EMD two cycles on railroad locomotives shows how the engine was redesigned several years ago and the Roots blower was removed. Large electric motors were installed on the turbos to bring them up to high speed so the 2 cycle engines would start. This is why the big ship 2 cycles have up to 55 percent efficiency. No loss from a positive displacement pump/compressor.
Pierce
The role of the blower on this (or any other 2 cycle Diesel) is to produce scavenging airflow. This is not supercharging, as the blower's capacity is carefully matched to the engine displacement so that a slight amount of positive air pressure is produced in the cylinders during the scavenging phase.
Talk:Detroit Diesel Series 71 - Wikipedia