radiator overflow mystery

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radiator overflow mystery

August 28, 2018, 03:03:44 pm

The saga continues. During our trip a couple of months ago, I reported a problem with coolant overflowing from the radiator cap and plastic overflow tank. The "thermos valve conversion" worked as advertised in keeping my coolant temps down and I was able to fix the radiator cap leak (with advise on this forum), but I still have a problem with the overflow tank overflowing.

We took the rig out for a test run with Kristi following me in the car. I had filled the metal reservoir, but the overflow tank was empty. After about three miles with the coolant temp at 156, she noticed coolant coming from under the rig. I pulled over and found that it had come from the overflow tank cap. On the way home, I pulled over and again looked at the tank. It was about 4" from the top and had not appeared to have leaked further. I had her run the RPMs up to 1800 while I watched the tank. The level did not change.

I had been concerned that there might be a head gasket leak that pressurized the cooling system under load, but this doesn't seem to be the case (I had run the tach up over 2000 on the way home with no resulting leak). Also, a mechanic also eliminated that with a pressure check while we were on the road.

Any ideas?

Re: radiator overflow mystery

Reply #1 – August 28, 2018, 03:30:42 pm

Sven,
You are having the same issues I had before finding the missing coolant flow orifice. Did you check to see if it is there. I chased this problem for seven years, before finding the answer.

BTW - I also thought I had a bad head gasket.

Cummins QuickServe Online | COLA

Re: radiator overflow mystery

Reply #2 – August 28, 2018, 03:54:19 pm

Quote from: Sven and Kristi – August 28, 2018, 03:03:44 pm

The saga continues. During our trip a couple of months ago, I reported a problem with coolant overflowing from the radiator cap and plastic overflow tank. The "thermos valve conversion" worked as advertised in keeping my coolant temps down and I was able to fix the radiator cap leak (with advise on this forum), but I still have a problem with the overflow tank overflowing.

We took the rig out for a test run with Kristi following me in the car. I had filled the metal reservoir, but the overflow tank was empty. After about three miles with the coolant temp at 156, she noticed coolant coming from under the rig. I pulled over and found that it had come from the overflow tank cap. On the way home, I pulled over and again looked at the tank. It was about 4" from the top and had not appeared to have leaked further. I had her run the RPMs up to 1800 while I watched the tank. The level did not change.

I had been concerned that there might be a head gasket leak that pressurized the cooling system under load, but this doesn't seem to be the case (I had run the tach up over 2000 on the way home with no resulting leak). Also, a mechanic also eliminated that with a pressure check while we were on the road.

Any ideas?

Sven, when you say overflow tank cap, are you referring to the metal tank? If so it is not working properly. When it get too much pressure the water goes to the plastic tank and it is not pressurized, it vents to atmosphere. The metal tank is not an overflow tank, more like a reservoir.

Re: radiator overflow mystery

Reply #3 – August 28, 2018, 04:17:26 pm

Quote from: Wattalife54 – August 28, 2018, 03:30:42 pm

Sven,
You are having the same issues I had before finding the missing coolant flow orifice. Did you check to see if it is there. I chased this problem for seven years, before finding the answer.
BTW - I also thought I had a bad head gasket.

Cummins QuickServe Online | COLA

I checked the link and found it listed as "Torque Converter Cooler". If I recall from earlier posts, it is near the thermostat and Richard Bark (fbark) showed me his when he was changing out his thermostat. Do you know how it works and why it increases the pressure in the cooling system? Also, why would it be missing?

Re: radiator overflow mystery

Reply #4 – August 28, 2018, 04:18:54 pm

Quote from: craneman – August 28, 2018, 03:54:19 pm

Sven, when you say overflow tank cap, are you referring to the metal tank? If so it is not working properly. When it get too much pressure the water goes to the plastic tank and it is not pressurized, it vents to atmosphere. The metal tank is not an overflow tank, more like a reservoir.

The overflow tank is the plastic tank. Some time ago, I replaced the cracked cap with the only other one I could find that would fit - a fuel cap.

Re: radiator overflow mystery

Reply #5 – August 28, 2018, 04:32:17 pm

Sven,
Please see the two attachments.
Why do I think it is missing? Because you have the exact same issue I did and mine was missing. Problem disappeared after installation!!!!!!!!!!!!!!!!!

Re: radiator overflow mystery

Reply #6 – August 28, 2018, 04:57:57 pm

Sven,
Our cooling systems are so well designed that the thermostat never fully opens or quite possibly closes completely under light load conditions ( flat terrain , going downhill). The thermostat is designed to start opening @ 180F-with full open @ 201F. As a result the torque converter cooler is not provided with adequate coolant. It is my belief that this condition causes the coolant in the torque converter cooler to overheat, raising the system pressure, forcing coolant out of the system. The bypass disc solves this problem.

Re: radiator overflow mystery

Reply #7 – August 29, 2018, 12:02:45 am

See my post of July 30 for pictures of where that restrictor is

Re: radiator overflow mystery

Reply #8 – August 29, 2018, 07:04:47 am

Fix the simplest issue first. Replace the radiator cap.

Re: radiator overflow mystery

Reply #9 – August 29, 2018, 12:01:45 pm

Here's the pictures again.

Re: radiator overflow mystery

Reply #10 – August 29, 2018, 12:22:51 pm

Quote from: amos.harrison – August 29, 2018, 07:04:47 am

Fix the simplest issue first. Replace the radiator cap.

This was the first thing done.

Re: radiator overflow mystery

Reply #11 – August 29, 2018, 02:20:59 pm

Sven,
Was the disc there?

Re: radiator overflow mystery

Reply #12 – August 29, 2018, 02:49:28 pm

Quote from: Wattalife54 – August 29, 2018, 02:20:59 pm

Sven,
Was the disc there?

You may be confusing me with Richard; I haven't gone into it yet.

Re: radiator overflow mystery

Reply #13 – August 29, 2018, 02:58:42 pm

You commented "This was the first thing done " following rbark's pictures.

I did not realize you were talking about the radiator cap. Your problem is like Déjà vu

Re: radiator overflow mystery

Reply #14 – August 30, 2018, 10:40:50 am

Quote from: rbark – August 29, 2018, 12:01:45 pm

Here's the pictures again.

rbark, did they put these disc in all motor combos. I'm having the same issue with my coach which has the detroit diesel ?

Re: radiator overflow mystery

Reply #15 – August 30, 2018, 01:09:25 pm

Quote from: Wattalife54 – August 29, 2018, 02:58:42 pm

You commented "This was the first thing done " following rbark's pictures. I did not realize you were talking about the radiator cap. Your problem is like Déjà vu

This is not about the radiator cap. I mentioned in my first paragraph that the cap leak had been resolved.

Re: radiator overflow mystery

Reply #16 – August 30, 2018, 01:40:36 pm

Yes I realize that!!!!!!!!!!

Re: radiator overflow mystery

Reply #17 – August 30, 2018, 01:47:56 pm

Quote from: Wattalife54 – August 30, 2018, 01:40:36 pm

Yes I realize that!!!!!!!!!!

I guess I didn't understand your previous comment.

Re: radiator overflow mystery

Reply #18 – August 30, 2018, 02:05:42 pm

Sven,

I dealt with the same problem from the time I purchased the coach in 2009. FT told me that I was losing coolant due to a bad cap. Multiple new caps later; the issue still existed. Many times I would walk to the rear at the rest stops and was greeted by a toad covered with coolant. The pressure was getting high enough to force coolant past the cap's rubber gasket, as evidenced by the spray pattern on the louvers. It's been about 2 years since I installed the bypass disc and have not lost a drop

Re: radiator overflow mystery

Reply #19 – August 30, 2018, 02:18:48 pm

Bob, thanks for the info. I'm on my third cap and finally got it to quit "spewing" when I followed a suggestion to bend the ears up a little. Seems to work well, no more cap issues as far as I can tell. I will replace the thermostat and inspect for the orifaced disc while I am at it.

Re: radiator overflow mystery

Reply #20 – August 30, 2018, 02:44:46 pm

Sven,
Like I said Déjà vu.
I bent the ears on the cap also. Made it tough to tighten. Never solved the problem, just reduced the frequency.

Re: radiator overflow mystery

Reply #21 – August 30, 2018, 04:15:14 pm

@tony, not sure about them being in all Foretravels. I think someone said they were used for coaches that had the trans retarder.

Re: radiator overflow mystery

Reply #22 – August 30, 2018, 06:45:02 pm

Air in the cooling system could push out. Mount a 5 gal catch container with the plastic overflow bottle output hose into the container to know how much and to capture overflow from the overflow.

Important to see if your radiator cap sucks back from overflow while engine coolant cools.

Always start with some coolant in overflow, otherwise air will likely be sucked into black metal pressure tank allowing cool coolant level to be low.

After a while your system may normalize.

Re: radiator overflow mystery

Reply #23 – August 30, 2018, 08:12:39 pm

Quote from: rbark – August 30, 2018, 04:15:14 pm

@tony, not sure about them being in all Foretravels. I think someone said they were used for coaches that had the trans retarder.

Thanks rbark, mine has a retarder, i will investigate!!!

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