National RV, Rear CAT overheats too easily

[Bonanza45D]

Me things I'm not alone on this issue. After doing all I could, even installing a Transmission Cooler (being the transmission that generates the most heat), my 300 HP CAT still overheats pretty easily. The Clutch Fan checks out fine; changed the anti-freeze and oil; changed all belts; water pump appears perfectly fine (70,000 mile on this 1999); everything is as clean as possible; new thermostat and hoses; tightly cowl fan shroud; and much more I can't remember after 2 years of chasing the issue!

Wagner Equipment (my nearest CAT Service) finally said, "... you know, just about every rear facing radiator tends to run hotter on these things ....". Oh great!

Indeed, it is slightly worse when I'm pulling my light weight enclosed trailer, probably further interrupting the low pressure area back there, but still.........

It appears to be a 'design flaw' mostly. Later model coaches utilize better cooling air flow from side mounted radiators. Rear facing radiators appear to be 'out of favor' anymore (understandably).

At this point, my only possible fix may be to install my own designed water injection system, whereas on command at the driver's seat, a solenoid will open, allowing the house pump to send water (via spray nozzles) down through the Fan Shroud, between the fan and radiator. In theory, this should knock the cooling temps down 20-40 degrees immediately, which is all I really need for some grades, etc. This is how its done on a dyno in a test cell. With 100 gallons of house water on board, why not use some of it periodically when I'm climbing grades or when the engine decides to run hot (which it does for no apparent reason at times on level highways). I operate at 6,500 ft, MSL, which may be contributing to the general overheating issue, but still................

Any other pusher types out there equally frustrated with overheating problems or that might have otherwise solved the problem? I'm guessing I might forge ahead with my cooling solution and post how it all works out afterwords. Surely won't hurt to try it (as compared to consistently overheating the CAT, I mean).

LKL

[MaverickBBD]

How often do you clean your radiator and CAC. I do mine twice a year with Simple Green and water and once a year with wet steam. Never had a cooling issue. I do watch my rpm's carefully when underload and will down shift to keep them up in the 1700+ range.

[VEG GUY]

Quote:

Originally Posted by Bonanza45D Me things I'm not alone on this issue. After doing all I could, even installing a Transmission Cooler (being the transmission that generates the most heat), my 300 HP CAT still overheats pretty easily. The Clutch Fan checks out fine; changed the anti-freeze and oil; changed all belts; water pump appears perfectly fine (70,000 mile on this 1999); everything is as clean as possible; new thermostat and hoses; tightly cowl fan shroud; and much more I can't remember after 2 years of chasing the issue! Wagner Equipment (my nearest CAT Service) finally said, "... you know, just about every rear facing radiator tends to run hotter on these things ....". Oh great! Indeed, it is slightly worse when I'm pulling my light weight enclosed trailer, probably further interrupting the low pressure area back there, but still......... It appears to be a 'design flaw' mostly. Later model coaches utilize better cooling air flow from side mounted radiators. Rear facing radiators appear to be 'out of favor' anymore (understandably). At this point, my only possible fix may be to install my own designed water injection system, whereas on command at the driver's seat, a solenoid will open, allowing the house pump to send water (via spray nozzles) down through the Fan Shroud, between the fan and radiator. In theory, this should knock the cooling temps down 20-40 degrees immediately, which is all I really need for some grades, etc. This is how its done on a dyno in a test cell. With 100 gallons of house water on board, why not use some of it periodically when I'm climbing grades or when the engine decides to run hot (which it does for no apparent reason at times on level highways). I operate at 6,500 ft, MSL, which may be contributing to the general overheating issue, but still................ Any other pusher types out there equally frustrated with overheating problems or that might have otherwise solved the problem? I'm guessing I might forge ahead with my cooling solution and post how it all works out afterwords. Surely won't hurt to try it (as compared to consistently overheating the CAT, I mean). LKL

I have seen this in the past it turned out that the blades on the fan are move able by loosening a bolt the blades are adjustable from pulling air or pushing air if the pitch was set wrong it won`t cool the motor! check it out you want it to push hard.good luck

[bucks2]

Pretty common complaint with rear radiators. If it didn't heat up when new, then I wouldn't think it's a design problem, but more of a maintenance problem. The usual response and what seems to work for most is thoroughly cleaning the CAC and radiation. Sometimes is requires physically taking them out to get all the caked on, baked on, gunk out of them. Every bit of road grime, oil, debris, dust, dirt etc can get sucked up and blown into the rad. Getting the corners spotless is as important as the middle. The coach is designed to use every square inch of rad space, it's all got to be clean.

It's a messy dirty job getting it clean, but more than likely that's where your problem is.

[Bonanza45D]

I am the second owner of this Coach. I have no idea if the previous owner had any overheating problems with the National. I HAVE in fact, replaced the Radiator and amazingly, there was no improvement on the overheating situation. There is always strong air movement through the radiator when standing behind the Coach and I keep the radiator clean. The CAC referred to here? Is that the Catalytic Converter? I've never cleaned it. Otherwise, what is a CAC?

[RustyJC]

CAC = charge air cooler, also sometimes known as an intercooler or aftercooler. The CAC cools the intake air after it is compressed in the turbocharger and before it enters the engine's intake manifold.

Rusty

[Vegasdan]

You didn't mention what Cat engine you have, 3126, C7, C9? My 3126 never over heats no matter what the ambient temp is, what I'm pulling or on any grade. Make sure your radiator is clean, shine a light through. If your slobber tube is too short you can build up alot of gunk in a short period of time.

[VanDiemen23]

water sprayers work. I have a 2gpm ag sprayer feeding a nozzle in the shroud. Takes about 10 deg off in 30 seconds or so.

[Bonanza45D]

Quote:

Originally Posted by VanDiemen23 water sprayers work. I have a 2gpm ag sprayer feeding a nozzle in the shroud. Takes about 10 deg off in 30 seconds or so.

NICE! Now that's encouraging VanDiemen23 and exactly the answer I was looking for (well, perhaps a better answer would have been an alternate fix, rather than a water injection system).
Listen, for all those that read this thread, "I absolutely have a clean radiator and CAC". We can take THAT series of suggestions off the table since that ain't the issue here, absolutely, without question! You can read a book through all of those fins! The radiator is NEW and the CAC is as clean as new! I've had both out; there is zero obstruction within; I never achieved any change in the engine operating temp after all of that effort. Go figure.
My engine is as 3126 CAT. I generally cruise the Coach at 65 mph on the highway (I don't push it hard).
I suppose my best bet, at this point, is to try the water injection system I've designed. Sorry answer, but oh well. I think it is a design flaw in the Coach, pulling hot air from the engine, transmission and pavement to cool the radiator. Huh? Yet 'some' claim to never overheat with the same design? Something ain't right!
I was hoping for a much lower drop using water injection (like 20-30 degrees), but heck, anything that achieves a drop in the engine's coolant temp and turns off the yellow check engine light will be a good thing. The whole thing has dogged me ever since I bought the Coach, 3 years ago. Should have sold it then! LOL

[flasher]

Had the same problem. I cleaned the radiator cooling fins and rerouted the crankcase breather tube to the back corner of the coach.the problem is hose ends just below the oil pan.when the oily film comes out of the hose it is blown right into the radiator the the oil collects dust and road grime clogging the cooling fins

[RLS]

You say that the thermostat is new, the 3126 has 2 thermostats. Are you sure that both were changed?

[VanDiemen23]

your altitude is also contributing to the problem. You should see less of a problem at lower altitudes

[bluepill]

Overheating causes can be quite difficult to pin down. Keep in mind that as engines age, some 'crud' can build up internally and reduce the ability to transfer heat to the coolant. Water pump impeller erosion can also cut down on flow.

If you have an external OIL cooler, make sure that it is spotless also. Any heat not removed from the oil can be transferred to the cooling system load.


It sounds like your idea for water spray may be the most effective solution at this point.

Best of luck.

[ImagineIF]

What engine dp you have and what temperature is it running. The newer engines run hot. My 2008 C-9 routinely runs 205 degrees, which is normal for the newer 2007+ EPA engines. So, for us coming from old school engines we think they should run at 180 degrees--not any more.

Gil