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Old 07-06-2020, 06:56 AM   #43
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I had a similar issue and it turned out to be a cracked reservoir that could not hold the pressure required. It was replaced and temp is under control now.

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Old 07-06-2020, 10:10 AM   #44
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Thermostat is stuck open not allowing proper cool down in the radiator. Temp Should cycle up and down as stat opens and closes.

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Old 07-06-2020, 10:20 AM   #45
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Write the date installed with a felt pen on all your filters.

This way you would have known whether the shop changed your air filter.
Ben & Sharon
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Old 07-06-2020, 12:26 PM   #46
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I had a similar problem. Turned out a squirrel or rat had built a nest between the cooler and radiator. Removed it and problem eliminated. Three different shops could not locate the problem before the 4th did.
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Old 07-06-2020, 01:06 PM   #47
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Now the nest is a new one

Had to be very aggravating
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Old 07-08-2020, 06:43 PM   #48
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Originally Posted by imnprsd View Post
A proper cooling flush can take 3-5 full cycles and 4-6 hours. How many times did you flush your system?

Does your engine have a coolant filter? ...Mine does, but some do not.

Did you use Restore-Plus when you flushed the 3rd time?

YES... on the thermostat. When you flushed your engine the first 3-5x this should have been replaced prior to adding your OAT coolant.

NO... on replacing the coolant. You just did so why go to the added expense? Just change your thermostat ($70) and see if you temperature problem is better.... then replace the air filter if needed. (Like Apatz said.) And top off with the same OAT coolant you used.

YES... to upgrading to a WAX valve when you get home. I don't have one of these in my Freightliner chassis, but every Monaco owner goes this route sooner or later based on what I read. But this is something you can do when you get home. For now, you should figure out how to but a band aide (work around) on your fan issue and later you might even find you get better MPG when you upgrade to a Wax Valve.

Yes... on the infrared gun if you continue to have problems on the road. Note: A low temperature area signals blockage, because there is no coolant in that area. Only $20 on Amazon and they can ship it to a big city locker.

Just a guess someone else can comment on: Isn't there a temperature sender that might be the problem with the fan clutch? IDK. I'm just throwing that out there.

Good luck. Keep us posted when you find your problem.

Note: I just saw this video that explains why the coolant reservoir - return flow/fill hose is so important. Check it out:

This is a 1-1/4" hose on my RV and maybe you have some blockage or it's collapsing?

Note: ISC and ISL are very close in most respects. So this video also applies to an ISL when you are trying to understand how your coolant system works.

That Wax valve is a completely different project and you need to do your homework on how to fix this as cheaply as you can.
Thanks so much for posting that. It links to other Cummins training videos that I'll watch as time allows. Very informative...especially how the thermostat works. If ours were ever to fail, I now understand that removing it (as one might do in a car) would be a terrible idea.
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Old 07-11-2020, 06:02 AM   #49
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My 97 American Tradition 300hp Cummins engine had the same problem years ago and it proved to be the cooling fan failing under load. As you described, driving on level ground was no problem until you started up a long grade and the alarm indicator would sound indicating an over heating condition. Changing the cooling fan solved the problem. Hope this helps.
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Old 07-30-2020, 07:29 PM   #50
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Just wanted to check in and update everyone that shared their ideas with us on how to resolve our overheating issue with our Monaco Camelot engine ( the Cummins 400 ISL)

We have taken most of the suggestions and done them with the last thing (should have been first probably) was to try and wash out the dirt in the radiator fins. We just did that project yesterday, but have not driven it yet so we still have hope.

But so far it seems we have increased our available horsepower with the Wax Valve install but the engine is still overheating. We did get a large amount of dirt out of the radiator but not sure what is normal and what is excessive dirt and grime.

If you want to see just what all we have done so far, we have a youtube channel we post our RV Adventure stories on and this video will most likely be one of our favorite.

If anyone has any additional suggestions please continue posting and we will hopefully eventually get it resolved. My wife does most all the driving but she has informed me that I will have to get back in the drivers seat if I dont figure it out soon.


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Old 07-31-2020, 07:58 AM   #51
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did you change the water pump ?
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Old 07-31-2020, 01:26 PM   #52
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Originally Posted by Phantom13 View Post
did you change the water pump ?
Thanks Phantom 13, We do have the water pump on the list of potential culprits but have not changed it out as of yet.

We have a 300 mile drive Sunday over more mountains (Bend OR, Portland OR ending up in Longview WA). I have spent quite a bit of time cleaning the radiator fins of dirt and debris and want to see if that helps, as there was considerable more dirt than I thought.

I also want to use our Thermal Temperature Gun on the Radiator to check for any Hot or Cold spots.

I have ordered a Photo Laser Tachometer to try and see what the RPM of the fan actually are now that we have changed over to the Wax Valve. At normal idle the fan turns fairly fast (although not nearly as fast as prior to changing to wax valve) and blows a fair amount of air.

But when I press the fast idle button, the fan RPMs drops down to maybe 10 or 20 percent of the normal idle speed resulting in very little air passing through radiator, and when I increase RPM substantially the fan remains at the same slow speed barely moving any air (like I think it is supposed to do)

BUT, I do not know if it actually goes up to Maximum RPMs once it gets up to the 200 degree engine temps or not and feel I need to insure the fan can actually spin at a couple thousand RPMs and do its job before moving on to the next potential weak spot in our cooling issue.

If the fan ends up operating as it is supposed to and the radiator does not have any hot/cold spots, then the Water Pump moves to the top of the list.

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Old 07-31-2020, 08:03 PM   #53
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When I went to the Freightliner class, we started talking about the cooling system. Mike started talking about using automatic transmission fluid. I raised my hand and said that my RV uses engine oil for cooling and power steering. He told me I was mistaken. I told him my sticker was blacked out and it had use engine oil. I was insistent and during our lunch break he did some checking. Come to find out my RV did use engine oil because hydraulic fluid would over heat on hills. I do not remember remember the tech number that was used to make it known that this was the fix for over heating on hills.
My engine was manufactured in December 2006.
You might check with Freighrtliner on this if you keep over heating.
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Old 07-31-2020, 10:32 PM   #54
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How was your air filter?
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Old 08-01-2020, 08:00 AM   #55
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JRPA, you mentioned you spent quite a bit of time cleaning the radiator fins. To do this right, you have to separate the radiator from the CAC (charge air cooler), transmission and AC coolers (depending on your configuration). The fins of each don't line up and it is therefore almost impossible to get the caked dirt and road oil out of the center of the stack. If your cleaning does not improve your cooling issue, since you indicated you cleaned out a lot of debris, don't overlook the probability that the radiator stack is still not flowing air adequately and the components need to be dropped out the bottom of the coach and cleaned separately both sides.

You also mentioned that you were going to use a thermal temp gun to check for radiator hots spots. The radiator sits in front of the engine fan, the CAC is generally outboard of that, and the transmission and AC coolers are usually on the outside. There is a shroud around your fan mating up to the radiator so I don't see how you are going to use a temp gun and get a series of test shots around the surface of the radiator. Maybe your layout is different.

I for one will be very interested in your drive results this weekend since I also have cooling gremlins I am fighting. So be sure to check back in with your results.

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Old 08-01-2020, 02:46 PM   #56
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Hi Bob - Enjoyed your YouTube - and salute you two not letting it get you down. Problems are opportunities!

Two out layers for you:

1) Temp Sensors can sometime act sporadically, and send bad info.

2) In addition to the water pump, I believe you've looked at the radiator return hoses, for higher volume collapsing/restriction. That's hard to do under the same conditions that could be causing the over heating. I believe cummins can do a '2-fer' for you, and hook up a test device to the radiator return hose to test water volume. This will test both the water pump, as well as it could possibly spot a collapse of the hose too.

Best of ongoing luck to you... Looking forward to your final resolution, as it could help others in the future!!!

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heat, heating, light, overheating

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