Cat 300 running hot on gradea

[fishingbob61]

In 90+ weather when pulling a long grade my 05 Bounder 34m with a 300hp Cat will run in the hot on the guage and the yellow light comes on, I will down shift and let up on pedal. When top of pull it cools down. I had it at Freightliner and they cleaned out the rad and cac and adjusted the water pump belt, helped some. Any thoughts?

[OLYLEN]

Just for a point of reference on the 3126 I had. Had radiator and C radiator clean boosted motor to 396HP and 1000+ torque, dyno, running in 90 degree climbs at 6-7% towing 7500# I could stay at 205 or so. It can be done, but everything needs to be running good. Don't think I've seen a stock a 3136 with a clutched fan. Also be pro active be at the best cooling speed at the hill not after your hot.

LEN

[fishingbob61]

I had Freightliner in Knoxville Tn.clean the cac/rad and do not know what they did. I will look under the bed and see what it looks like. I will be going up on the mountain on the20th and see what happens. Thank all for your replies and yess I pull the Tahoe.

[DSDP_Don]

Bob....Your issue is pretty much the exact problem that most of these Cats experience when the radiator is dirty. For peace of mind, I would lift the bed, remove the engine cover and take a flashlight and look between the CAC (charge air cooler) and radiator. Yo don't say what they did to clean your radiator, but unless they pulled that engine cover and spent a lot of time washing and rinsing, or pulled the radiator, it's most likely not clean.

There is only about 3"-4" between the two cooling units. With a flashlight you can look between them. If they look like they're growing hair, they were not cleaned properly.

[Passin_Thru]

My 500 CAT runs 230. Cat said to run it that hot out west on the grades.

[slickest1]

The harder you are pulling the more heat it will build. It may hold at a certain speed climbing a hill but if it is lugging along at a lower rpm it will build more heat. When in very hot weather it adds to the problem dramatically. Shifting down alows it to pull the hill easier and not build as much heat plus your fan is cooling better at the higher rpm.

[wallynm]

Plus if you are towing the Tahoe you are close to the GGWR I suspect which just adds to the load. We always down shift at the beginning of long grades.This engine has two thermostats that Cat recommends changing out at regular intervals.

[wolfe10]

OLYLEN wrote:
If memory serves your best cooling RPM is at 2200 RPM. Settle into a gear that allows the 2200 RPM then you can start playing in that RPM range with and up shift or speed up a touch to see if it stays cool.

LEN

Depending on HP rating, the peak HP on the 3126 is between 2200 and 2400 RPM.

Totally agree that RPM needs to be toward the upper end of the usable RPM range, but with peak torque at 1,440 RPM, IMO 2000 is a good compromise between cooling and fuel consumption (higher RPM= more fuel consumption).

If 2000 RPM at less than wide open throttle overheats, determine the cause and fix it.

#1 cause is blockage of the front of the CAC

#2 cause is slipping V belt-- on that engine there is a separate V belt that ONLY drives the water pump. It is MANUALLY TENSIONED.

#3 cause is one or both of the thermostats (Caterpillar calls them regulators) hanging up/not opening fully. Yes, some have a single thermostat, some two. Any Caterpillar dealer can get you the correct ones (and a gasket) from your engine serial number.

[OLYLEN]

If memory serves your best cooling RPM is at 2200 RPM. Settle into a gear that allows the 2200 RPM then you can start playing in that RPM range with and up shift or speed up a touch to see if it stays cool.

LEN

[Mandalay_Parr]

The chassis manufacturer designs and installs the cooling system.and radiator, not the engine folks.
Suspect some of the designs are not overly generous.

Jerry Parr

[fishingbob61]

Thank all of you for your replies, I will try down shifting earlier and get the rms up.

[hostage]

flagstickfrank wrote:
I've driven a 300 hp CAT for 15 years and if you go up hills at full, or near full, throttle it will heat up. You have to keep a close eye on the gauge, when it starts to heat up you just downshift and slow down. My fan is direct drive and the only way to cool the engine is to bring up the revs. In some cases I'm in the truck lane but I don't overheat and we get to where we're going without a tow.

kinda what I thought but did not want to suggest;; I had a 1997 side cool 325 ISC and it did exactly the same thing. like a 300 cat trying to move a load on hot days up a grade that its basically not really designed to do in those conditions

[flagstickfrank]

I've driven a 300 hp CAT for 15 years and if you go up hills at full, or near full, throttle it will heat up. You have to keep a close eye on the gauge, when it starts to heat up you just downshift and slow down. My fan is direct drive and the only way to cool the engine is to bring up the revs. In some cases I'm in the truck lane but I don't overheat and we get to where we're going without a tow.

[hostage]

wolfe10 wrote:

hostage wrote:


seeing as the rad etc is clean the only thing I can think of is the fan clutch is weak and slipping ?

Two points:

Most rear radiator coaches have direct drive fans, not clutched fans. Yes, there are a few, particularly newer ones that are clutched.

While cleaning the radiator is important, it is critical to understand the the vast majority of the blockage will be on the FRONT (toward front of coach) of the CAC (Charge Air Cooler) which can only be accessed from the front (through the bedroom or closet).

I have more practise on side cooling but the few rear I have seen are clutch controlled hence my comment;also the OP clearly said the CAC was cleaned so one has to assume it was done and done correctly

[wolfe10]

hostage wrote:


seeing as the rad etc is clean the only thing I can think of is the fan clutch is weak and slipping ?

Two points:

Most rear radiator coaches have direct drive fans, not clutched fans. Yes, there are a few, particularly newer ones that are clutched.

While cleaning the radiator is important, it is critical to understand the the vast majority of the blockage will be on the FRONT (toward front of coach) of the CAC (Charge Air Cooler) which can only be accessed from the front (through the bedroom or closet).