Foretravel Owners' Forum

Kent, I cobbled up a spray system for the 12V in the MCI, total cost about $25.00, worked great, I found water corroded my special spray nozzles, switched to window washer fluid, no more clogging em up, worked beautifully, easy to reduce temps by 20 deg or more with flip of switch. Everyone that looked at it laughed and copied it.
The rich folks bought the fancy commercial products.  Me, picture cheap  & tacky  ;D
FWIW

Lots of good replies and information!  Just want to pass on an experience I had like yours with a sob coach some years ago, same engine as yours.  Like you, climbing a mountain, downshifted and turning around 2000 RPM, overheated.  Took it to a Cummins dealer for a check up and described what had happened.  After finding nothing wrong, they said, try to stay close to the maximum TORQUE RPM for your engine, around 1500, when under a heavy load.  Barry and Cindy had it right with their post.  Downshift as needed, use partial throttle if necessary to stay close to the peak torque rpm, NOT the rated horsepower rpm.  Worked for me! Using that technique, I have (knock on wood) never had another overheat on any of my RV's. That is not to say that you could not have a partially blocked section of the radiator, or some other problem.  But if nothing is found, try this. 

On the C-8.3 Cummins engine, at what RPM is the max torque? And what is the max hp RPM?

Well, lots of response to my post, including Brett Wolfe, who I consider to be a real guru and have learned much from his posts!  My post was not intended to be a technical review, but an anecdotal experience.  Brett, yes, the water pump is pumping more coolant at high RPM, but is the coolant able to absorb significantly more heat at the higher flow rate?  And, is the radiator able to expel this heat?  I think your conclusion is close to mine, except you recommend using the higher RPM.  If you find yourself climbing a grade and overheating, I would say, back off the throttle, downshift, maintain about 75% throttle and try to keep the RPM at peak torque, -0+250 RPM by down or up shifting.  When the engine is making less power (but more torque), it is making less heat.  This is a matter of balancing the heat production with heat dissipation, while maintaining enough power to continue moving ahead.  By the way, if you find yourself climbing a grade and not overheating, keep going! Also, this is anecdotal to operating 5 coaches over a lot of years. This is for those who do have a problem!

I had many customers leaving the desert in the summer at dawn to avoid the temp gauge moving much.  Waste of time.  No cooling system in an Rv does not get to 230 or more used hard. 

Not like your car where the gauge never moves.  100 deliveries.  Told every one to drive it harder.  If the engine temp goes past 230 or 240 and continues to climb then back off and down shift.

Bob

Kent,

You are correct.  In fact, I would not run any engine over 210 without taking some measures to mitigate temperature rise.

Above 220 and you get into the "what can I get away with", rather than "what is best for engine longevity".

Brett

Bob, everything I have read about the 6V92 has said letting it run over 210 degrees can result in real problems. Now I hear from you and Wayne Musser at Foretravel that the area of concern is really 230 to 240. I guess the correct answer is to take the conservative approach and keep it cool but I sure would be much more relaxed when traveling knowing for sure that higher temps in the Hot Hot summer were OK and not harmful. Is the 230/240 limit your opinion or is there something official from Detroit that can make me more comfortable.


Sorry about busting the thread but I have this thing about engine temperature.

To Quote Bob: "Every motorhome owner is too paranoid about the temp gauge IMO. I ran all these really hard for hours myself to test them as they were my demos and owned by foretravel and the other companies and never had a single issue and neither did any of the customers I ever educated. Like I said if it runs 210 up a hill at 70 degrees and 240 at 100 degrees it's relative and within the design limits of the coach."

With many years experience with the DD engines, I see the 240f temps as one of many reasons Foretravel went broke, nothing like a salesman to help sink you.
No one runs a DD into that temp range without it getting shut down by the DDEC system.
Just one more reason for all the humor.
Dave M

To Quote Bob: "Every motorhome owner is too paranoid about the temp gauge IMO. I ran all these really hard for hours myself to test them as they were my demos and owned by foretravel and the other companies and never had a single issue and neither did any of the customers I ever educated. Like I said if it runs 210 up a hill at 70 degrees and 240 at 100 degrees it's relative and within the design limits of the coach."

Now I am somwhat confused, as I frequently worry about my C8.3 Cummins' temp as I approach the crest of a steep and/or long grade and the engine temp creeps up toward 205-210. The temp alarm begins chirping at about 210 and is full blown by 215. Are you saying that I can ignore the alarm and don't have to pull over to let the temp return to normal (i.e. 190-195) levels? Or were your comments restricted to CAT and Detroit Diesels?

If what you relate is correct, even for Cummins engines, I would want to shut down (greatly reduce) my alarm volume, as it is irritating at the least and anxiety-producing at the most.

I REALLY appreciate you sharing with us your experiences with many FT's over the past couple decades. It has enriched my understanding of this great product.

Dave, I'm betting Bob treats his own U320 the same way he has discussed. One has to go by their experience and his has been that pushing temps above 210 has not been harmful. I'm guessing that your vast experience related to high running temps with diesel engines on generators and OTR trucks is much more extreme than the occasional high temps we experience with our coaches. I'm still going to go by your recommendations just because I don't want to make an expensive mistake, but I'm sure Bob's experiences dictate a different approach to the high temperature running of our Foretravels.

I wish I could relax and just cover up the coolant temp gauge, but that will never happen.

Bob, Do not confuse a marine engine with a highway engine, while they look the same, they have vastly different horsepower ratings BECAUSE they have a massive cooling body of cooler water, and NOT a minimal sized radiator.
Dave M

You can get away with 240 deg F for a little while, but you're almost certainly increasing piston ring wear, promoting cylinder liner scuffing, burning more oil, oxidizing your oil, and increasing carbon buildup in your piston ring grooves.

Engine cylinder liners are designed so that the heat transfer across the liner, from combustion chamber to engine coolant, maintains the temperature at the inside top of the liner to 400 deg F or less. If the temp exceeds 400 deg F, then the oil film at the top of the cylinder liner will flash off and the top ring on the piston will momentarily weld itself to the cylinder liner on the combustion stroke where the top ring is under the greatest load. This is the Top Ring Reversal condition and it's the most critical thermal loading in the engine.

If the manufacturer says that you're coolant temps are good to 210 deg F and derates at 215 deg F and you override this and continue to 240 deg F, then the heat transfer across the top of the cylinder liner will be impacted. The inner cylinder liner wall will see a corresponding increase in temperature and you run the risk of flashing off the oil film. So it's not a "relative" temperature issue. It's an absolute temperature issue. You can only let the top inner surface of the cylinder liner hit an absolute max temp that's less than the oil flash temperature spec, regardless of outside air temperature. Otherwise you're absolutely increasing wear on the engine.

Can you get away with it for a short period? Probably, but you're definitely shortening the life of the engine.

David Brady
'02 Blue Bird, Wanderlodge, LXi, NC

Bob,
Thank you for sharing your experience with us.  I enjoy reading your posts on other subjects as well and feel we are fortunate to have someone on the forum like yourself.  I spoke with an owner of an identical coach to mine who was the original owner and told me he tested the heck out of it during the first year (while under warranty) to make sure there were no overheating issues.  He told me of the same experience you talk about and he had owned the coach for 10 years when I talked to him back in 2001 and there was no apparent damage to the engine. 

Even so I couldn't help but be worried when I saw my engine temperature go to 215 and I would slow way down or pull over.  It's hard to ignore the advice of the manufacture especially when it's such a costly repair.  I added a water system and a digital temperature gauge that would turn the water on at a programable set point but was still not satisfied with it as a long term solution.  Five years ago I added a side radiator (in addition to the OEM rear radiator) with electric fans that did the trick - just 2 weeks ago, the engine reached 212 F on a mountain grade in So. Cal. with outside temp at 102 F.  The other thing I think about is how the inner walls of the engine cooling passageways are probably not conducting heat as well as they were when new - some 21 years ago.

The only way I can reconcile the difference between your experience and the published data is the published limits may reflect business decisions as well as practical ones and the real world is full of shades of gray.  I have to say I think I will feel  a little more at ease when I see those high temperatures after reading your posts knowing there is probably more margin there that what I believed before.

Kent,
In my coach book there's a manual "Series 92 Field Maintenance Recommendations" booklet (published by DD) that has temperature charts for 12 configurations of cooling systems.  Every one has "MAX. TEMP" at 210 F and "ALARM" at 215 F.  It also shows that a 180 F thermostat will start opening at 180 F and be fully opened at 197 F.  It also shows most "modulating" fans "start" at 190 F and are "full" at 202 F

Bob,

When I bought my coach in 2006, I talked to Bruce Mallinson at Pittsburgh Power about turning up the M11.  He discouraged me, saying he didn't know anyone pushing that engine.  Of course, he is building drag racing trucks using N14's etc.

The way these things are designed is that there's a max temp for the coolant entering the radiator top tank. This temperature is related to the the heat transfer across the upper cylinder liner required to stay below the oil flash point as described earlier.

Then there's the maximum outside air temperature at which the coolant system can still maintain the maximum upper tank temp. Of course, there's some reserve built into the coolant system to compensate for scaling and other environmental degradation.

The usual condition is a coolant system that's able to maintain the max upper tank temp within the ambient temperature. Once you go outside the ambient temperature capability, then you're no longer operating within the design of the coolant system. Your in an open loop condition.

Given the coolant systems reserve capacity and given the margin built in to the upper inner cylinder liner temps there's a safety factor designed in, but when you're running at temps that exceed the ambient capability of your coolant system, then the coolant system top tank and cylinder liners will track ambient conditions as Bob pointed out. At some point the lack of lubricating oil at the top ring and the lack of oil heat sinking at your main and connecting rod bearings will result in thermal runaway and your temps will no longer be stable. The trouble is recognizing this condition.

In addition to this there's exhaust gas temperatures and oil temperatures to consider.

Here's an idea, change your oil and do 10 climbs up 17 mile Baker grade in California in the summertime flat out, then have an oil sample analyzed. I'd be looking for a marked increase in wear metals.

It's fun colorful reading, but it isn't science.

David Brady
'02 Blue Bird, Wanderlodge LXi, NC

Something else to keep in mind is the location where the coolant temp sensor is positioned in relation to the hottest internal engine surface. Generally the sensor is far away from the upper cylinder liners. So why do manufacturer's derate at 220 deg F? Probably because the coolant temp at the cylinder liner is much higher and risks localized vaporization. We know that a 50/50 concentration of EG and Water will boil at around 260 deg F with a pressure cap of 15psi. Do the manufacturers allow 260 deg at the cylinder liner? Probably not. Manufacturers need to back off to a lower temp at the cylinder liner, something like 230 deg F. This gives a margin of safety for unknowns in the real world, unknowns like the condition of the owners coolant, cooling system, radiator cap, scale inside the coolant system and engine coolant passages, and even insulating crud and scale on the coolant temperature sensor itself. Remember, Bob is primarily talking about running customer's brand new equipment up 17 mile Baker grade, sometimes under the watchful eye of the OEM. Is this is something we want to recommend for someone's older motorhome. I'll let you decide.

Thanks Bob, I truly do appreciate your input and I take you for your word. No offense, just trying to shed a little insight into the workings of the system. :)

Thanks Gary Bouland, I really do like the Foretravel brand. It's another great American Icon. :)

David Brady
'02 Blue Bird, Wanderlodge, LXi, NC