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Old 05-09-2021, 05:55 PM   #1
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Radiator overflow tank leak

Im not to familiar with cooling systems or diesels. On my Cummins 360HP diesel, there is a tank which I'm assuming is the overflow tank for when the radiator coolant heats up. It's at the rear of the engine compartment and seems to be there for keeping coolant topped off, just the same as gas engines. Anyway, it has a cap that has the usual ears to twist it down tight onto neck of the tank. The base of the neck has a hairline crack maybe a quarter inch long that bubbles ever so slightly at normal operating temps. Is this a must replace now item (is it compromising the radiator pressure system?)? Or can it wait until the next scheduled maintenance in a few thousand miles? The coach is 12 years old with 72,000 miles. I've only had it a year and 3,000 miles.

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Old 05-09-2021, 06:33 PM   #2
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My Cummins / FreightLiner has an expansion tank that is different than a conventional overflow tank.
The expansion tank is directly connected to the radiator and has a pressurized radiator cap on it... it is the way to fill the radiator.
Overflow tanks have a hose that allows coolant that escapes the radiator pressure cap to be collected and drawn back into the radiator when it cools and draws a vacuum.
They serve similar purposes but work slightly different.
If you have an expansion tank a leak will cause you to lose pressure and the system won't work properly unless it is fixed or replaced so it holds pressure.

Overflow tanks aren't pressurized and may not be a problem if the leak it near the top.
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Old 05-09-2021, 06:42 PM   #3
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From your description you have a pressurized tank, based on the style of cap. The tank needs to be replaced because if it canít build up pressure it will allow the coolant to boil at a lower temp which is not good for the engine or for the coolant pump.
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Old 05-09-2021, 07:02 PM   #4
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Here is a good source for a replacement source, suppliers and prices change all time so check around.

https://shop.findmyrvparts.com/searc...h=tank&Submit=


In your case I would consider changing. I changed mine about 6 years ago.
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Old 05-09-2021, 07:31 PM   #5
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Steve the surge or expansion take in you MH is the same principal as that in your car. In order for your cooling system to function correctly it needs to hold pressure. It is common after several years and the vibration of use that the plastic tanks fail and need to be replaced. Is it urgent? Well if its leaking fluid I would keep an eye on it and replace as soon as practical. If its cracked its only going to go in one direction. I did not see you mention what chassis but there is no down side to calling the Chassis manufacture and picking up the part and having it on hand. Then you can get it replaced on command. But i would at least get the part on hand asap.
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Old 05-09-2021, 08:24 PM   #6
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I have a Freightliner RR8R chassis and a Cummins ISC 360 8.3L engine. Who do I call for the expansion tank? I think it might be a nylon tank according to what I see on the link that was posted in the reply above. And of course, that one is dis-continued and replaced by a steel tank. And 3X as expensive.
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Old 05-09-2021, 08:28 PM   #7
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Call freightliner directly to get a part number, they are very helpful, you just need the last 6 of you VIN number
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Old 05-09-2021, 08:29 PM   #8
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Quote:
Originally Posted by Leonandlisa View Post
Call freightliner directly to get a part number, they are very helpful, you just need the last 6 of you VIN number
Thank you!
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Old 05-09-2021, 10:01 PM   #9
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An rr8r chassis is made by roadmaster unique to monaco, you may want to call cowlaw salvage, the roadmaster tanks are becoming rare, source engineering has a replacement. Travel buddy when I lived in CA had same issue on a 05 diplomat, we ended up using one from a wrecked Volvo class 8 truck.
Good luck the monaco degass bottle has 3 hoses, 2 small on the top and one large 3/4 inch hose on the bottom.
Best of luck!
Quote:
Originally Posted by pflightnut View Post
I have a Freightliner RR8R chassis and a Cummins ISC 360 8.3L engine. Who do I call for the expansion tank? I think it might be a nylon tank according to what I see on the link that was posted in the reply above. And of course, that one is dis-continued and replaced by a steel tank. And 3X as expensive.
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Old 05-09-2021, 10:09 PM   #10
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Quote:
Originally Posted by pflightnut View Post
I have a Freightliner RR8R chassis and a Cummins ISC 360 8.3L engine. Who do I call for the expansion tank? I think it might be a nylon tank according to what I see on the link that was posted in the reply above. And of course, that one is dis-continued and replaced by a steel tank. And 3X as expensive.
You have a roadmaster chassis, not a freightliner. If you can post a picture, someone will direct you, but there are many sources. Keep the same style and size and it's an easy swap. I replaced my plastic tank with a stainless tank a few years ago from Source Engineering in Oregon, but there are many other suppliers.
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Old 05-09-2021, 10:15 PM   #11
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If you could post a photo here more people could offer you more targeted suggestions.

If you have a spring loaded (pressured) cap on the neck of the coolant reservoir, that cap is due for a replacement, any auto part store should have it. Then the overflow container would be like this and cheap to replace -
https://www.amazon.com/Dorman-603-00...verflow&sr=8-5
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Old 05-10-2021, 04:22 AM   #12
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Major brain cramp!! I do know I have a Roadmaster chassis. I read it right in the manual before posting. Must have been sleep deprivation or power of suggestion... thanks for the help. I'll post a pic later today.
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Old 05-10-2021, 11:38 AM   #13
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Quote:
Originally Posted by pflightnut View Post
I have a Freightliner RR8R chassis and a Cummins ISC 360 8.3L engine. Who do I call for the expansion tank? I think it might be a nylon tank according to what I see on the link that was posted in the reply above. And of course, that one is dis-continued and replaced by a steel tank. And 3X as expensive.
If you have a Monaco coach and the RR8R chassis, it's NOT a Freightliner. RR8R is a Monaco-built Roadmaster chassis designation.


Edit: Oops! Should have read to the bottom of the thread before posting this. Sorry for duplicating a previous post.
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Old 05-10-2021, 01:15 PM   #14
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This is the expansion tank and cap. Anyone know of a source that is economical. Or perhaps a sealant such as Seal All or JB Weld for the base of the neck?Click image for larger version

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