Cummins C8.3 325 hp running too warm

Topic: Cummins C8.3 325 hp running too warm (Read 1829 times) previous topic - next topic

Re: Cummins C8.3 325 hp running too warm

Reply #25 – August 07, 2020, 04:16:28 pm

Thanks, Barry. I appreciate your input - a lot.

Larry

Re: Cummins C8.3 325 hp running too warm

Reply #26 – August 07, 2020, 04:37:58 pm

Quote from: Barry & Cindy – August 06, 2020, 05:01:44 pm

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.

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.

Re: Cummins C8.3 325 hp running too warm

Reply #27 – August 07, 2020, 04:46:13 pm

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.

Re: Cummins C8.3 325 hp running too warm

Reply #28 – August 07, 2020, 04:56:46 pm

Manual recommends going to neutral between r and d.

Re: Cummins C8.3 325 hp running too warm

Reply #29 – August 07, 2020, 04:58:36 pm

Quote from: Realmccoy – August 07, 2020, 04:56:46 pm

Manual recommends going to neutral between r and d.

YUP.

Re: Cummins C8.3 325 hp running too warm

Reply #30 – August 07, 2020, 05:21:10 pm

Quote from: wolfe10 – August 07, 2020, 04:37:58 pm

...the transmission is designed to shift under full throttle-- both up and down shifting. Does this on most all shifts as one accelerates...

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.

Re: Cummins C8.3 325 hp running too warm

Reply #31 – August 07, 2020, 05:44:30 pm

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

Re: Cummins C8.3 325 hp running too warm

Reply #32 – August 08, 2020, 12:31:15 am

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

Re: Cummins C8.3 325 hp running too warm

Reply #33 – August 08, 2020, 08:38:04 am

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.

Re: Cummins C8.3 325 hp running too warm

Reply #34 – August 08, 2020, 09:36:28 am

We are assuming it's a figure of speech calling the engine a supercharger.

Re: Cummins C8.3 325 hp running too warm

Reply #35 – August 08, 2020, 09:41:15 am

John,

The Detroit 6V92 has a supercharger/blower not a figure of speech.

Mike

Re: Cummins C8.3 325 hp running too warm

Reply #36 – August 08, 2020, 09:45:55 am

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.

Re: Cummins C8.3 325 hp running too warm

Reply #37 – August 08, 2020, 10:09:48 am

When in cruise and the engine shifts down it is with full throttle so I wouldn't worry about it.

Re: Cummins C8.3 325 hp running too warm

Reply #38 – August 08, 2020, 10:35:02 am

Learned something new about the Detroit.

Re: Cummins C8.3 325 hp running too warm

Reply #39 – August 08, 2020, 10:52:48 am

Quote from: John44 – August 08, 2020, 10:35:02 am

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.

Re: Cummins C8.3 325 hp running too warm

Reply #40 – August 08, 2020, 11:07:46 am

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

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

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

Re: Cummins C8.3 325 hp running too warm

Reply #41 – August 08, 2020, 01:56:07 pm

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

Re: Cummins C8.3 325 hp running too warm

Reply #42 – August 08, 2020, 02:52:26 pm

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.

Re: Cummins C8.3 325 hp running too warm

Reply #43 – August 08, 2020, 07:44:56 pm

Chuck : Yes It looks just like the picture.

Re: Cummins C8.3 325 hp running too warm

Reply #44 – August 18, 2020, 06:38:10 pm

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?

Re: Cummins C8.3 325 hp running too warm

Reply #45 – August 18, 2020, 07:01:59 pm

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.

Re: Cummins C8.3 325 hp running too warm

Reply #46 – August 18, 2020, 09:07:32 pm

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.

Re: Cummins C8.3 325 hp running too warm

Reply #47 – August 19, 2020, 01:23:24 am

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??

Re: Cummins C8.3 325 hp running too warm

Reply #48 – August 19, 2020, 01:27:37 am

I should say voltage drop

Re: Cummins C8.3 325 hp running too warm

Reply #49 – August 19, 2020, 08:36:30 am

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.

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