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coolant tank

Hi guys,anybody know why my coolant tank with the sightglass would run low but the plastic overflow tank remains full? maybe radiator cap?
Ron & Bette Ringhand previous/1979 33 ft appollo/ 1993 gv u240/ 2003 40ft beaver Marquis/1993 gv u300 40 ft

Re: coolant tank

Reply #1 –
When my former 08 Nimbus was doing that, a new radiator cap fixed it. So maybe...
Keith and Dawn Hudson #18766
Current- 1999 U295 DFGE 40ft. - Build #5405
Coach Name: 4BUS4US
Previous- 2008 Nimbus CE338: 40th Anniversary Edition- Build #6486. 
Toad: 2021 Jeep Cherokee Trailhawk

 "I know something about a lot of things..a lot about something's..and everything about nothing "

Re: coolant tank

Reply #2 –
Could be a bad spot in the hose that goes between the 2 tanks.

Mike

Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: coolant tank

Reply #3 –
Quote from: rinron –
Hi guys,anybody know why my coolant tank with the sightglass would run low but the plastic overflow tank remains full? maybe radiator cap?

Easy to explain:
If there is enough air volume in the cooling system (excluding the overflow tank) it will ABSORB the expansion/contraction of the coolant with temperature change.

Anytime the level in the coolant tank/overflow bottle doesn't move between cold (lower) and hot (higher) YOU NEED TO CHECK COOLANT LEVEL IN THE SYSTEM ITSELF.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: coolant tank

Reply #4 –
Yep, bad cap or hose would explain the full plastic tank.  Can you still see coolant in the sightglass?
Dave and Kelli
1997 U295 40' Build #5188 CSGI
1995 U240 36' Build #4621 SBID-SOLD
2006 Jeep Wrangler Rubicon

Re: coolant tank

Reply #5 –
Quote from: Dave Larsen –
Yep, bad cap or hose would explain the full plastic tank.  C

OR air in closed part of cooling system.

Agree, a broken hose between closed cooling system and overflow would also explain it.

Can't see how a bad cap (won't hold PSI) would do it-- that would likely give MORE movement in the overflow reservoir.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: coolant tank

Reply #6 –
I worked on an 03 u320 a couple of years ago and the hose between the plastic tank and the metal tank was completely plugged and wouldn't let fluid flow between the 2 tanks.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: coolant tank

Reply #7 –
Quote from: red tractor –
I worked on an 03 u320 a couple of years ago and the hose between the plastic tank and the metal tank was completely plugged and wouldn't let fluid flow between the 2 tanks.

WOW!

So the PSI of the cap (10+PSI) would not overcome the blockage in the hose?  Sure sounds like a very neglected cooling system-- but no big surprise.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: coolant tank

Reply #8 –
Yes it was, it had not been serviced in a very long time. Also the air dryer had not been serviced and the air in the wet tank had lots of water in the tank, so that the drain in the bottom of the tank was blocked with sludge.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: coolant tank

Reply #9 –
Quote from: wolfe10 –
Can't see how a bad cap (won't hold PSI) would do it-- that would likely give MORE movement in the overflow reservoir.

If the cap is a recovery cap and one of the seals is bad...

Years ago there were some posts about someone using the wrong radiator cap (non-recovery) and running into this issue.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: coolant tank

Reply #10 –
Thanks for the ideas.There is coolant in the sightglass.The cap is old and crusty so will replace.
Ron & Bette Ringhand previous/1979 33 ft appollo/ 1993 gv u240/ 2003 40ft beaver Marquis/1993 gv u300 40 ft

Re: coolant tank

Reply #11 –
Quote from: wolfe10 –
OR air in closed part of cooling system.

Agree, a broken hose between closed cooling system and overflow would also explain it.

Can't see how a bad cap (won't hold PSI) would do it-- that would likely give MORE movement in the overflow reservoir.

If the cap is bad, coolant can't be drawn back into the steel tank when it cools down to ambient temperature.
Dave and Kelli
1997 U295 40' Build #5188 CSGI
1995 U240 36' Build #4621 SBID-SOLD
2006 Jeep Wrangler Rubicon