Detroit 6-71 that sits a lot

[Chad Duncan]

I live aboard a 1959 gmc PD-4101, an old highway bus. It's powered by a Detroit 6-71 and although the bus is roadworthy, I only take it out once a year or less. I am wondering if there is something I should be doing to keep the engine in as good of a condition as possible. Should I start it and run it up to temperature on some sort of schedule? Anything else I should be doing for long term storage?

 

[Birken Vogt]

I would start it, let it warm up a few minutes at idle, then run at elevated RPM for a while to get it as good and hot as you can. Maybe engage the transmission (if automatic) at idle for a few minutes of this. Maybe every couple of months. This engine has a fuel rack that is prone to sticking from disuse which then causes the engine to rev to the moon and blow up when started in this condition.

 

[old-iron-habit]

I dought that you will get that 6-71 up to a decent temp idling or even revved up without a load on it. Prolonged idling will lead to wetstacking, a condition in which unburnt fuel will slobber out of your tailpipe. If it slobbers long enough it will run like crap, and smoke like hell for a bit under load. Run it hard and the slobber will sort itself out and blows that crap out. The best way is to take it out and use it once in a while. A road run will also help keep the seals, brakes and everthing else from seizing up or leaking from setting. I make a somewhat educated guess that it is a reverse rotation sideways mount 6-71 at the rear of the bus. Not many of them around anymore. Good luck and post some pictures when you have it out and about.

 

[Birken Vogt]

I agree, try it once and if it never warms up, then don't keep doing it, just start it every 2 months, smack the throttle open a few times to make sure the linkages are freed up and the fuel and oil are still moving around, and try to keep run time to minimum until it is time to drive somewhere.

 

[kshansen]

All engines do not like to be run under low or no load conditions, but I think the Detroits are about the worst ones in that regard. Even with coolant temps up to the normal operating temps the pistons and cylinders will still be comparatively cold. Reason being with the two stroke design the blower is pushing just as much air through the cylinders and out the exhaust valves at no-load as it is at full load. This flow of air keeps the cylinder walls and head surface nice and cool as very little fuel is needed to spin the crankshaft at 2,100 rpm.

Now on the other hand if you had a 4 stroke turbocharged engine it would be a little less of a problem as the flow of air through the engine is somewhat reduced under low power operation as the turbo does not really start pushing the air to the engine till there is some serious heat energy in the exhaust. Still not good to run at low power conditions just not as bad.

The following is somewhat off topic but got in to the "vent mode"

The worst Detroit I ever saw was a 3 or 4-53 running a genset. Our company decided to use this to run some block heaters on a 3412 Cat and a few security lights over nights and weekends for a portable Black-top plant operation. I doubt that engine was running anywhere near 10% load for hours on end. They tried replacing the little N-45 injectors with N-35's to no avail. See smaller injectors only reduce the maximum horse power, the governor controlled the rpm and therefore the amount of fuel injected was probably the exact same! That poor engine looked like someone had mixed a solution of coal dust and fuel oil and dumped it over the top .

Myself and at least one other guy tried to talk them into something but never could convince them to let us try it. The plan was to install a restricter plate in the exhaust between the manifold and the muffler. The idea was to cut back on the air flow through the engine thereby reducing the cooling effect on the cylinder walls. But these people we the same ones who could not be convinced the way to make the engine quieter would be to install an intake silencer. No they had me add a second muffler in series with the original one. Noise was twice as bad next to the air filter than standing outside the trailer next to exhaust pipe!

 

[John C.]

Back in my nautical days we had two FairBanks Morse 38D8 1/8 engines for emergency power and had the very same problem. They were 1,000 KW and meant for one very serious problem, something about reactors melting down being possible. At any rate they were run at times to power the ship. Usually when we were in the states and there wasn't enough shore power available. Problem with that was everything else on the ship was shut down. Only the lights and a few electric heaters were running so the engines only pull maybe 250 to 300 KW. The mufflers were mounted horizontally and measured around eight foot in diameter and twelve foot long. There was a pipe off the bottom of the thing and a big valve with a pipe plug. After a couple of days of running like that we would put a five gallon bucket under the pipe and open the valve a bit and drain three or four gallons of fuel diluted engine oil out. We never could make the ocifers understand about load, heat and diesel engine efficiency.

As all the previous posters have said, you need to fire that thing up and get it hot now and then. Take a weekend every quarter year and run it a couple of hundred miles.

 

[td25c]

I live aboard a 1959 gmc PD-4101, an old highway bus. It's powered by a Detroit 6-71 and although the bus is roadworthy, I only take it out once a year or less. Should I start it and run it up to temperature on some sort of schedule? Anything else I should be doing for long term storage?

That's interesting that you live in the bus .
I might install some carbon monoxide detectors when running the engine with the bus sitting still & make sure you have good ventilation in case of an exhaust leak .
Do you plug in to an outside source for electricity similar to a motorhome ?

About the Detroit engine , keep the fuel tank full to help prevent rust . As mentioned fire it up once in awhile & let it run half hour to help keep batteries charged so she's ready to roll when ya need it to .

Detroit's are pretty simple and reliable engines built for any application . You wont hurt it running wide open throttle or idling all day long . They built for it and test of time proved it years ago

I fired up my GMC truck " 6 V 53 engine " one morning to air up a low tire on my pickup before heading to a job .

Between cell phone calls that morning & getting the tire aired up I forgot to shut off down the GMC & left for the job site .
Funny part is the Old Man called me around 4:00 PM that afternoon asking " is there any reason the GMC is running " ?
No ..."Just go ahead & shut it off Dad ".

Detroit ran most of the day idling no different then in a crane . Burnt a little fuel but engine is fine . LOL!

 

[RZucker]

And how big were the puddles under the airbox drains?

 

[td25c]

The GMC marked its territory in the shed RZ .
Few shovels of fine aggregate each time and I will end up with chip & seal floor in the shed . ( Grins )
Think positive
I can just imagine the look on the Old Man's face when he noticed the truck running & nobody around

 

[RZucker]

I was just pokin' at you in fun. But I worked for an outfit that had a water truck with a 6V92T that would come into the shop clean but even with the air precharged and ready to go that thing would leave 2 trails of oil all the way to the gravel when you backed it out. Blower seals were good but the oil rings must have been gone. Get it out and romp it a time or 2 and she was ready to work with hardly a drip.

 

[Truck Shop]

I knew RZ and td25c weren't going to let this thread slip by. How have you been doing td25c, don't see you on HTF.

Truck Shop

 

[td25c]

No doubt RZ . The older I get the easier it is to laugh at myself Bro !

That's interesting about the water truck with the 6V92T dripper .
My GMC is actually pretty tight for the most part about oil usage .
The FWD rig up truck is a " dripper " . http://www.heavytruckforums.com/showthread.php?51-Fwd-Trucks&p=1251&viewfull=1#post1251
What's strange is both trucks have same engine (6V53 ) and injectors ( N45's )
The FWD has a noticeable power advantage for some reason ? The engine has a real crack when you step on the throttle compared to the GMC . Both trucks have good exhaust systems & muffler .

 

[td25c]

I knew RZ and td25c weren't going to let this thread slip by. How have you been doing td25c, don't see you on HTF.

Truck Shop

No way we can let a Detroit thread go by Truck Shop .
We are still doing same old stuff just different day moving into the future running old Detroit & Cummins power trucks /equipment . It works for us so will probably " stay the course " for the duration .
Will get back on Heavy Truck Forums in the near future . Really enjoy that forum as well .

 

[RZucker]

No way we can let a Detroit thread go by Truck Shop .
We are still doing same old stuff just different day moving into the future running old Detroit & Cummins power trucks /equipment . It works for us so will probably " stay the course " for the duration .
Will get back on Heavy Truck Forums in the near future . Really enjoy that forum as well .

Hey... We are the Detroit Dudes. Weird as that may be.

 

[Chad Duncan]

Thanks for the advice guys.