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Topic: Radiator Cap (Read 649 times) previous topic - next topic

Radiator Cap

My radiator cap upper seal is deteriorating, which has started me down another rabbit hole. After reading many old posts on the subject, I still can't figure out what to do. Here's the clues:

The cap I have has an upper seal (the seal between the radiator neck and the outside world) made of brass, not rubber. Other than "AO" stamped on the top center of the cap, no pressure rating. I've pushed on the spring and it's pretty stiff, there's never been any coolant leaks, leading me to think it's a 15# type (the system has inched close to 200f a few times this summer going over passes). Also, there's no coolant reservoir, although there is what appears to be a fitting for one on the radiator neck, and the inner brass disc on the cap is spring-loaded, suggesting that it's made for one.

I've found a website "Northern Radiator" which can give me a part number based on radiator neck dimensions, but I don't know what pressure rating to go for, or if I should have the type for a coolant reservoir (and then install one since it's missing).
1991 Grand Villa 36' of Freedom
Detroit 8.2 turbo, Allison 4 speed
Model G91382636SBIORED8.2
Oshkosh Chassis VC20RD2

Re: Radiator Cap

Reply #1 –
Take it to NAPA. They probably have it.
1993 U225 Build #: 4285
500 Watts Solar
Honda CRV AWD
Former 1981 Foretravel Travco
Retired, Full Time Off Grid Snowbird

Re: Radiator Cap

Reply #2 –
Mine is a NAPA balkamp 703-1427 radiator cap. Keep in mind mine is Detroit with a rear radiator. They can mic out the bottom part of the cap and get you going.
92 Grand Villa
Silver 6v92
 side isle.
build# 3973

Re: Radiator Cap

Reply #3 –
I took my radiator cap to NAPA today and they could not help. We compared the 703-1427 to my original and they look very different. Not sure if I should or shouldn't try it. The gasket on the original is starting to deteriorate so I know the replacement day is approaching.
Does anyone have a 2001 U270 ISC 350 and have a part number?  I could sure use the some direction.
Greg
Greg & Sandy
2001 U270
Build # 5803
Eagle, Idaho

Re: Radiator Cap

Reply #4 –
We also have the rear radiator Detroit configuration. I had tried NAPA, but they couldn't help. I then took the old cap to a local diesel repair and parts shop, and they had no idea what the "AO" stamp meant. They did have 2 choices of cap in stock that fit, a 7# and 10#. I went for the 10# and we'll see how it goes.

While I was there I asked about the missing reservoir and the fitting on the filler neck. He told me it's not uncommon on older rigs not to have a reservoir, but couldn't explain why there would be a fitting. I've gone ahead and put in a make-shift reservoir (an old plastic jug) and rigged it up with some tubing.
1991 Grand Villa 36' of Freedom
Detroit 8.2 turbo, Allison 4 speed
Model G91382636SBIORED8.2
Oshkosh Chassis VC20RD2

Re: Radiator Cap

Reply #5 –
Quote from: Byron Sharon & Isaac –
We also have the rear radiator Detroit configuration. I had tried NAPA, but they couldn't help. I then took the old cap to a local diesel repair and parts shop, and they had no idea what the "AO" stamp meant. They did have 2 choices of cap in stock that fit, a 7# and 10#. I went for the 10# and we'll see how it goes.

While I was there I asked about the missing reservoir and the fitting on the filler neck. He told me it's not uncommon on older rigs not to have a reservoir, but couldn't explain why there would be a fitting. I've gone ahead and put in a make-shift reservoir (an old plastic jug) and rigged it up with some tubing.
If the cap doesn't have the secondary rubber gasket at the cap above the spring gasket, it will not be able to pull liquid back when it cools.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Radiator Cap

Reply #6 –
That's what I thought. What's interesting is that I've never seen any leaks after driving, suggesting that the pressure in the system was never high enough to push up the spring in the old cap. I put in the reservoir mainly to see what happens with the new cap.

How does one find out what the normal pressure range is supposed to be inside a cooling system? It seems to me that the cap's job is to prevent over pressuring the system (and blowing out hoses or the radiator), which makes me a bit concerned that the old one never leaked any coolant after some of our hotter summer drives.
1991 Grand Villa 36' of Freedom
Detroit 8.2 turbo, Allison 4 speed
Model G91382636SBIORED8.2
Oshkosh Chassis VC20RD2

Re: Radiator Cap

Reply #7 –
The pressure caps job is to raise the pressure in the system to raise the boiling point of the coolant. If the coolant doesn't boil there is very little loss of coolant. The newer systems allow for expansion into the recovery bottle while hot and returns the overflow back to the system when it cools. Protecting hoses, etc is not the intention of the cap.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Radiator Cap

Reply #8 –
My radiator coolant temp recently got up to 225 and I lost coolant but it DID NOT go into the recovery bottle. It came out via the cap. Fortunately I watch my oil & water temps like a hawk. I replaced the cap but I don't understand how the coolant could not go into the recovery tank, as designed, unless the hose from the radiator to the bottle is plugged. Is there another possibility?
1993 U225 Build #: 4285
500 Watts Solar
Honda CRV AWD
Former 1981 Foretravel Travco
Retired, Full Time Off Grid Snowbird

Re: Radiator Cap

Reply #9 –
Does your radiator cap have the second rubber gasket against the cap? If not the coolant will just come out the cap.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Radiator Cap

Reply #10 –
Mine does.
1993 U225 Build #: 4285
500 Watts Solar
Honda CRV AWD
Former 1981 Foretravel Travco
Retired, Full Time Off Grid Snowbird
 

Re: Radiator Cap

Reply #11 –
15 lbs is very common for radiator caps. .Each pound raises the boiling point by 3 degrees. If you run 50% antifreeze you gain another 10 degrees. So 45 plus 10 is 55 degrees plus 212 for water is 267 degrees  before boiling.  Once the coolant  boils it can no longer pick up the heat from the engine and internal damage occurs.  But internal  combustion engines lie to run hot, a 195 degree thermostat is what I run. If the rad is in good shape, no problem. Removing the thermostat will often  cause overheating as the  coolant passes through the radiator to quickly to dissipate the heat.
Dave
Safe Travels
2001 U320 40ft
Build #5867
2003 Tracker
VE7DOD