Engine/Transmission (1998.5 - 2002) High fuel temperature?

[jmblitz]

Does anyone know what the typical fuel temperature spec should be for a 99 Ram 2500 with the Cummins turbo diesel?

 

[WestTN]

I read the fuel heater spec's in the service manual a couple of years ago. I think it said the heater was designed to heat the fuel to around 160 degrees.



The cooler the fuel runs the higher the pressure drop across the fuel filter. And we all know we need all the pressure we can get from the stock delivery system.

 

[jmblitz]

I was concerned with the fuel temperature being read by the sensor in the IP, I've been having an intermittant power loss problem. I just can't bring myself to condemn the VP-44 at this point, I am also suspecting an ECM problem. Symptoms: P0216 with an associated P1689, fuel temperature has been averaging 120 degrees F at normal cruise speeds, 65 mph, I work 125 miles from home. LP is intermittant also with KOEO, cycle time on a crank-but no start is about 39 seconds instead of the usual 25 seconds. I'm fabricating a BOB right now to make signal acquisition easier. Anyways just the usual problems with this generation, I still love the truck though.



Jerry

 

[csevers]

Two summers ago I watched my fuel temps with a scanner and I don't think that I ever saw more than 112 f on a very warm summer day with a less than a 1/2 tank of fuel. Not sure what the spec is.



Craig

 

[tractorface]

Most large diesel engines used in things like generators have a max inlet fuel temperature recommendation of 160. I don't think the VP would like anything over that and well below that would be nice. You only want to heat it enough to filter properly. The OEM fuel bucket does not do much to help dissapate heat, you end up running hot fuel. I suspect on a truck with an OEM fuel bucket you would see temps at the supply to the VP well in excess of 100 degrees. Trucks with simple pickup tubes and no buckets should not see temps much higher than ambient unless running close to empty. Cool is good as long as it is warm enough to filter properly. Say 50 degrees or so is what I have heard for good filtering

 

[scotty1]

Something I have been discovering is that if we have too much pressure to the pump, we will work against ourselves with heated fuel.

On my 01 after a hard 3 hour run towing in the mountains at 17,000 pounds, the temp in the fuel tank was 180F! I would venture to guess the fuel gets heated and the excess gets returned and as the volume in the tank gets lower, it reheats and recirculates hotter fuel... a vicious cycle.



After I lowered the fuel pressure of the Holley Blue it came back down to the 150-160 range and the next day after most of the heat disipated from the tank I netted 110-115F in the tank.



Then I turned the pump back up with the other spring and turned up the TST and ran that way for 3 hours... the temps were only slightly lower... 10 degrees... 170, perhaps because I was using a bit more fuel. Very close to the same amount of fuel in the tank too.



On the 04 Ram I have had steam rush out of the tank when I open it to fill after a hard pull. I will take temps on the next road trip and adjust the new pump I am testing at different pressure levels and see if too high of pressure is causing that on the 3rd gens too.



Scotty

 

[tractorface]

Curious how/where you measured the fuel temps. Was it in the "bucket"? or in the return line? Supply? Interesting data, I think that is the type of thing that would explain some VP failures. Inadequate cooling

 

[RobertHunt]

My sons 2000 diesel is showing loss of fluids. Had a new radiator put in last July. Had it checked a month ago when it started losing fluid. The couldn't find the leak but replaced a petcock that was used to drain and the radiator cap. Now its again losing water . It ataarted to run hot today and then cooled down after a while. where is the fluid going as we don't see sign of anything leaking.

My email is -- email address removed --

 

[scotty1]

Curious how/where you measured the fuel temps. Was it in the "bucket"? or in the return line? Supply? Interesting data, I think that is the type of thing that would explain some VP failures. Inadequate cooling

We tried an infra red... aimed at the tank... not very good. LOL



Then I borrowed a digital with a long copper probe. Since the trucks are 4x4 I can get at the top of the tank [room for my carcass to get under there easily]... where I had another fitting for a bigger auxilary pick up. I just took out the bolt/plug and pushed it in there. I also could feel that the tank was hot. This was the initial reason I wanted to check this out... I was under the truck working on some wiring and when I put my hand on the tank... IT WAS REAL HOT!

 

[scotty1]

My sons 2000 diesel is showing loss of fluids. Had a new radiator put in last July. Had it checked a month ago when it started losing fluid. The couldn't find the leak but replaced a petcock that was used to drain and the radiator cap. Now its again losing water . It ataarted to run hot today and then cooled down after a while. where is the fluid going as we don't see sign of anything leaking.

My email is -- email address removed --

I think I might know where the coolant is going.



My 01 had an empty overflow all the time. I would top it up and after a few days I was adding more. What caused the loss of coolant was a head gasket leak forcing air through the radiator and blowing the coolant out of the bottle.

After I o-ringed the head with a stock gasket, I never had the problem again.



Scotty

 

[jmblitz]

I used the watered down iformation from the IP fuel temp sensor using a scan tool.

 

[R-N-R]

I still wonder how many LP/VP failures have been reported from people returning fuel to their aux tank. The theory being that the hot fuel goes to the aux tank which replenishes the primary tank, thus less recirculation of warm fuel to the VP.

 

[WestTN]

Given that the fuel heater is designed to bring the fuel t o168 degrees ( if I remeber the exact number ) I doubt that 180 degrees is too hot. Remember, these things are made of metal, not skin, muscle and bone.

 

[tractorface]

Got a spec sheet for a Cummins QSXK-78 in front of me and it states max inlet temperature at 160. The electronics don't like the heat. Why on earth would anyone heat the fuel to 168, makes no sense . If that is what the heater is designed to do someone needs to be fired :-laf . We package diesel gensets all day long. Most have fuel coolers on the return to keep the fuel temps reasonable. Heating it enough to properly filter in the winter is all that needs to be done. The VP44 has tight tolerances and a green board so keeping it from getting real hot is a good idea. I find it hard to believe the OEM heater is capable of raising temps as much as stated. Wish I had not given mine away, I would investigate further. Next time I talk to a Cummins fuel system engineer I will ask.

 

[darkhorse]

tractorface is on to something about the electronics in the VP44. The guys at Greasel tested an '01 to get it to run on straight veggie oil. The motor ran great but the electronics in the IP failed. They concluded the hot fuel was the problem.

 

[scotty1]

The 'Green Board' is one of the weakest links in the VP-44, its very vulnerable.

I have seen a few that had browning on the board... meaning HOT!



I always wondered why the ECM was bolted to the side of the block too.



I think that when you are towing hard and the fuel is recirculating quickly, it only adds to the heat issue. I also think that the fuel pressure vs volume is more important then we all first thought. More pressure does not mean more fuel... it does mean more pressure and possible more entrained air as well as more stress on any lift or pusher pump and lower GPH. There is a fine line that needs to be figured out on these trucks... it would be different for every after market application too.



I looked into the return line going to a big AUX tank and then let it dissipate in there then transfer over to the factory tank. I never did it but I had the theory in mind that it would help... I had all the fittings and hose, then I sold the truck when the 04 arrived. Maybe I can run a temp gauge in the AUX tank to a gauge in cab? Would a Pyrometer be ok to use?



I will look at doing this with the 04 as I will be towing HEAVY this summer.



Scotty

 

[darkhorse]

The 'Green Board' is one of the weakest links in the VP-44, its very vulnerable.

I have seen a few that had browning on the board... meaning HOT!







I'm not very knowledgable about the innards of the VP44. Would there be any way to remotely mount the "green board" to get it away from the heat?

 

[tractorface]

I agree. Just running big pressure causes heat. Ideally you would want adequate flow at a lower pressure. Put your thumb over the end of the supply line and the pressure will soar. Remove the VP and the pressure will drop like a bomb but you will have lots of fuel on the ground. I plan to put a temp gauge on my fuel supply and play with pressures etc. Not sure what good it will do but... .

 

[ThrottleJockey]

Any of you guys think a fuel cooler is over the top? Or is it just one of the many things a VP-44 needs to help it out as far as reliability, longevity?



Brian

 

[tractorface]

Not over the top at all. Industrial diesel engines use them all the time. Most of the gensets we deal with have them installed on the Return line. Fuel Gelling due to a cooler will not be an issue. The cooler can't take that much heat out of the fuel. To be honest other than Scotty1 I have not seen any data on this subject as it applies to our trucks. After Scotty1 posts I think the cooler may be a real good idea. First and foremost you need to eliminate the Hot Fuel Bucket problem. Our trucks have a return that dumps into a 2 quart size container that the supply line feeds from. On 2nd gen trucks there is an unused capped line that drops down outside the bucket, this could be used to at least let the return fuel circulate with the entire contents of the tank. I know my little Iseki Diesel tractor runs like garbage when the fuel gets low due to the extra heat. Would love to see some Cummins data on the effects of hot fuel on the ISB