I have had my RV for 12 years and I think I learned something new.From the very first month I had the RV I experienced overheating when traveling in temps over 100 degrees outside.I have a CAT C7 and the temp alarm trips at 220 degrees.I took it in to FL and they showed me how both radiators were caked with oil, dirt and road debris, and they cleaned it all out.I then found out my oil sump was not plumed to the end of my RV, so the oil that comes off this hose was going directly into the fan and onto the radiator. I fixed this by having it plumed to the end past the radiator.Then once a year I break out the simple green and clean both the radiators.All has been good for a while.This month I decided to go to Northern AZ.I'm heading north on 17 going up, up, up.Then I hit this really steep grade and the temp starts going up, up up.I manually downshift to 3rd gear to keep up the momentum.The temp goes to 222 degrees.I try something I never tried before, I downshift to 2nd gear and let off the gas a little so the transmission is not trying to go to 3rd gear.When all of a sudden the engine temp start to drop, and keeps dropping all the way to 213, well below the overheat alarm.So now I'm thinking I should downshift to 2nd gear when I hit these really steep grades.Did I finally figure out how to drive my RV correctly in this situation ?Let me know, and please refrain from saying "yes stupid" or "it only took you 12 years to figure this out, DUMMY ?"

Less fuel or less load = less heatSlowing down and dropping a gear does great things. It can be hard to keep engine and/or transmission temperatures in check during the summer months.

You summed it up pretty good...... I mean the down shifting even lower part.:B

Bottom line: It takes XX HP to climb a grade. If you generate that HP at 2000 RPM instead of 1600 RPM, the FAN and WATER PUMP are turning 400 TIMES A MINUTE FASTER.Also, on the Caterpillar 3127/C7, check that the separate water pump belt (manual tensioner) is not loose. A slipping water pump belt will overheat.BTW, most of your cleaning is on the FRONT of the CAC (Charge Air Cooler). It is the first thing in the air flow from the fan.

Did I finally figure out how to drive my RV correctly in this situation ? YEP.........The climb out of the Verde Valley going north can get ya!

wolfe10 wrote:Bottom line: It takes XX HP to climb a grade. If you generate that HP at 2000 RPM instead of 1600 RPM, the FAN and WATER PUMP are turning 400 TIMES A MINUTE FASTER.Works the same for a gas coach also. Down shift and get the RPM up. It's not a race to the top and if it is you're using the wrong vehicle to win the race.

Proper Shifting to Reduce Engine Temperature | Good Sam Community

hipower
Explorer
Jul 29, 2016
J-Rooster wrote:
hipower wrote:
Those of us who have some trucking experience in our backgrounds drove when pyrometers were prevalent. Measuring your exhaust temperature was almost a neccesity to keep from cracking a piston or exhaust manifold in the early days of turbocharging OTR diesels.

I don't recall the exact temps suggested but they were different depending on the probe placement, pre or post turbo. Somewhere in the dark recesses of my mind I think it was 1200 degrees pre turbo and 800 degrees post turbo, but I can't swear that is correct anymore.

The key here is that if your EGT was too high you downshifted a gear and backed off on the throttle to keep the EGT in an acceptable range. Using our coolant temps to guide us is just a less accurate way of doing the same thing.

Bottom line, if you experience temps that make you uncomfortable while climbing a grade downshift and reduce throttle input to bring the temps back down.
J-Cat, glad to hear that your really learning about your CAT Motor and what it takes to get it running good. Highpower, those were the good old days! Keeping those diesel motors right on 2150 RPM's and if you shifted into neutral with the Jake Brake on it would kill the motor! My boss perfered us to take our foot off the throttle when the pyro got to 1000.

Those were interesting days indeed Rooster. Naturally aspirated diesels making 250 HP or less in most cases. Gas engines that were lucky to make 150 HP. Five speed main transmissions with three and four speed auxiliary boxes or two speed rears. Putting the diesel fuel to them to where there was a black cloud of exhaust that nearly blocked out the sun when you pulled away from a stop and at every shift and a foot of fire coming out the stack lighting up the night sky. Cabs so hot in the summer you could hardly stand it and so cold in the winter you couldn't take off your coat and gloves and an interior ice scraper was almost a neccesity. Big loads and brakes that were barely passable on the level and scared the **** out of you in the mountains.

Makes me understand that the good old days weren't really all that good, but we had fun and made a little money along the way. Today you have a hard time finding drivers or 'wanna be' drivers that can even shift a manual transmission. Nostalgia is a wonderful thing and our memories only seem to keep the good and forget the bad.
SoCalDesertRid1
Explorer
Jul 29, 2016
Gears are a torque multiplier. When you shift to a lower ratio gear, you have greater torque multiplication. Therefore, the engine doesn't have to work as hard when operating in lower gears. This means less heat made by the engine.
Snomas
Explorer
Jul 29, 2016
I've been down shifting for 14 years to lower temp. When you live in Colorado you learn to do that very quickly !
wolfe10
Explorer
Jul 29, 2016
Just to clarify terminology, on a rear radiator diesel:

Behind the fan is the CAC (Charge Air Cooler). It is an air to air cooler for clean air coming from the turbo and going to the intake manifold.

Behind that is the Radiator. This is the one with coolant in it.

Air flows from the front (actually from under the coach) through the CAC and then the radiator and then exhausts to the back of the coach.
JCat
Explorer III
Jul 29, 2016
Triker, did you even read my original post, it talks to each one of your items.

The only thing I did differently this time was go to 2nd gear and slow down.
I always downshifted to 3rd when going uphills.

As far as cleaning the radiator from other posts, I spray and clean from the front and back of both radiators.
J-Rooster
Explorer
Jul 28, 2016
hipower wrote:
Those of us who have some trucking experience in our backgrounds drove when pyrometers were prevalent. Measuring your exhaust temperature was almost a neccesity to keep from cracking a piston or exhaust manifold in the early days of turbocharging OTR diesels.

I don't recall the exact temps suggested but they were different depending on the probe placement, pre or post turbo. Somewhere in the dark recesses of my mind I think it was 1200 degrees pre turbo and 800 degrees post turbo, but I can't swear that is correct anymore.

The key here is that if your EGT was too high you downshifted a gear and backed off on the throttle to keep the EGT in an acceptable range. Using our coolant temps to guide us is just a less accurate way of doing the same thing.

Bottom line, if you experience temps that make you uncomfortable while climbing a grade downshift and reduce throttle input to bring the temps back down.
J-Cat, glad to hear that your really learning about your CAT Motor and what it takes to get it running good. Highpower, those were the good old days! Keeping those diesel motors right on 2150 RPM's and if you shifted into neutral with the Jake Brake on it would kill the motor! My boss perfered us to take our foot off the throttle when the pyro got to 1000.
wolfe10
Explorer
Jul 28, 2016
OK, a little more detail.

Wally is correct-- lower RPM= better MPG.

But (yes, LARGE BUT) if coolant temperatures rise, MPG is a LOT less important than keeping the engine from overheating.

So, indeed if coolant temperatures are not rising, low RPM is the ticket (as long as it is above peak torque RPM-- for Cat C7 that is 1,440 RPM).

If temperature starts to rise, downshift to raise RPM's and back out of throttle. Yes, lower MPG, HAPPIER ENGINE!
wallynm
Explorer
Jul 28, 2016
We run ours a ~ 1600 RPM which is much closer to peak torque which is 1450 RPM.

tinkerer wrote:
That is exactly the same thing I do when climbing that same grade. I like to keep the rpms at 2000 or above. This also a C7 Cat.
hipower
Explorer
Jul 28, 2016
Those of us who have some trucking experience in our backgrounds drove when pyrometers were prevalent. Measuring your exhaust temperature was almost a neccesity to keep from cracking a piston or exhaust manifold in the early days of turbocharging OTR diesels.

I don't recall the exact temps suggested but they were different depending on the probe placement, pre or post turbo. Somewhere in the dark recesses of my mind I think it was 1200 degrees pre turbo and 800 degrees post turbo, but I can't swear that is correct anymore.

The key here is that if your EGT was too high you downshifted a gear and backed off on the throttle to keep the EGT in an acceptable range. Using our coolant temps to guide us is just a less accurate way of doing the same thing.

Bottom line, if you experience temps that make you uncomfortable while climbing a grade downshift and reduce throttle input to bring the temps back down.
4x4van
Explorer III
Jul 28, 2016
ricelake922 wrote:
This article is very interesting but if you have automatic how do you downshift to help the engine overheating issue?

Seriously?

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