Hi all. We took our new 5th wheel (11.5k loaded) out for it's maiden voyage last weekend and the truck pulled it fairly well except for when we got to a looong steep grade - about 7% for 12 miles. Normally, the temp would be dead on 190 or a little less but when we hit the grade and the trans shifted out of lock and/or into 2nd gear, the temp started to slowly climb and went out of the safe range. We pulled over, put it in neutral reved the engine a bit but that didn't pull it down much, but id did a little. When it was back in the safe range I shut it down for about 10 min. and it dropped back to safe. We made it to camp and once unhitched the truck drove and shifted fine, no trans fluid loss. My question is what could cause this? The whole way, the temp was fine until we came out of lock or went in to 2nd gear. I was thinking maybe fan clutch or t-stat. A friend told me there was a heat exhanger on the side of the block where the tranny cooler lines are run and that the hot trans fluid (when not locked up) could cause the engine coolant to get hot. I looked for it but couldn't find it.

Any advice for a new 5th wheel guy?

Thanks, Mike.

 

My bet is on heat from tranny. Autos produce a lot of heat.

 

you should get a stick drive

 

Unfortunately, I'm stuck with an auto so I'd like to make it as effective as possible. Does anyone know if the '99s have an external air cooler for the trans or are they run thru the radiator. I see 4 radiator looking guys - the radiator, intercooler, AC condenser, and one more which I'm thinking would be the trans cooler but have been told it could be the hydraulic brake boost cooler. Anyone?

Thanks, Mike.

 

The automatics do generate a lot of heat when the converter is unlocked,but the temperature shouldn't go out of the safe zone. There are a couple of things you can check.

1. Look for the crankcase vent bottle on the front of the engine cover. If it is there you will need to clean the back of the radiator. It will be clogged with oily dust. Then move the bottle as described in other threads. Search for puke bottle.

2. Make sure your fan clutch is locking up. You should have heard the fan roar when the overheating occurred.

With all that said, 7% is a pretty steep grade. Was it a hot day when this happened?

 

Thanks WestTN, yeah - it was fairly warm; around 87*. I checked the back of the radiator - no oily dust; the bottle was removed and just the hose is there draining to the open air. I did hear what I think was the fan clutch but can't be sure if it was engaging. When I turn it, there is resistance on it. I wonder if I should just replace it since it's the original unit.

 

I noticed you have 285 tires and 3.54 gears. If you were going slow enough to be in 3rd, pull it down into 2nd with the shifter and that will bring your rpms up and help keep things cooler. Just don't redline the motor. The 285 tires and 3.54 gears hurt at the lower speeds. Ive done the shift to 2nd gear allot and it helps keeps the temps from coming up so fast.

 

The stock torque converters are a cheap inferior product. Get a triple disk converter and a switch to manually lockup when needed for towing. 3.73 rear gears helps quite a bit. That year engines have their sweet spot around 2000 rpm. With 3.73 gears that is 67 MPH. You can easily go slower and still have RPM in the better economy range of 1800 to 2100. Issue 47, page 106 of the TDR Quarterly Magazine has a graph showing fuel consumption lb/BHP-HR.

 

67HotRod, that's exactly what happened - the RPMs were a little low so it went into 2nd; about 2200 RPMs, maybe a little more.. it was pulling steady but the temps kept rising. Kinda making me think it might be a fan clutch?

 

Your converter unlocks in second gear and creates a tremendous amount of heat. I doubt your cooling system can handle that much for any length of time. Your tranny sure can't and will burn up eventually. A manual lockup switch can keep it locked when in second and will prevent burning up your tranny.

 

Good info - where can one obtain a "lockup switch"?

 

Be careful too about stoping and shutting down to let it cool. You could potentially burn up your turbo. The turbo will be so hot, it will cook the oil out of it and then you restart on a dry turbo. theres a cool down timer you can add to help with avoiding cooking a turbo.

Also reconsider looking at the radiator. At the least, leave it full, but loosen the mounts and look at the front of it. You can lean it back enough to do this. The back can look clean, but the front can be caked full of crud.

 

What he said the front of the radiator is what gets a build up of oil and crud from the vent tube. Very common problem.

 

You guys all need to take into consideration that the radiator is at the rear of the A/C cooler and the charge air cooler and on the auto's is handling the trans also. The radiator is the last in line to get any sort of cool air after its passed thru the other two coolers. The load, gears and grade all play into the equation as well as a stock trans. Outside temps are also a factor as are the tire size creating an even taller gear ratio.
This also doesn't take into consideration the condition of the coolant, thermostat, fan clutch or radiator blockage. I think the next big move should be a tranny upgrade and the other's should all be checked out.
PS. Also, the added frontal area of the fifth wheel is also adding resistance when in motion unless you are accompanied by a steady tailwind matching your forward speed further taxing your equipment.
Sorry, I rambled but just some thoughts to ponder.

Kurt

 

7% grade, 12 miles, Fairly heavy load, second gear to maimtain some speed, engine slightly oveheating, tranny temp light on. It sounds normal to me. You can only expect so much from a mere machine with design limitations. If you don't want to spend money, just slow down a little and run in 1st gear. i pulled an extreme load in low gear and 3200 RPM to get over hill. Engine was getting hot but tranny light did not come on. Took several minutes to cool also. Read owners manual about hot shutdown time. A very large cooler would help a little or a deep sump pan.