Radiator Cap is Leaking

[Beatty1950]

Sent: 1/2/2005 1:30 AM

My 1975 D19 Brave with a 318 Dodge engine developed a leaking Radiator cap on the cap that is on the top of the radiator.  My Radiator setup has 2 caps.  One is the front of the radiator and the other is on top of the radiator.

Before I make the investment in a pair of new Radiator caps, I thought be to check with the Winnebago team to see there is anything special about these caps.

Today when I drove MissTank, there was a blow over leak ov Antifreeze.  I think the seal on the cap is worn.

Any suggestion would be appreciate.  I could always just buy the same cap as currently installed but I thought chance that the existing cap was wrong.

Dave Beatty

[HeavyHaulTrucker]

Sent: 1/2/2005 8:43 AM

Dave, according to the Auto Zone catalog, there are two choices:

Part Number 7816 -- 16 lb Cap w/ Pressure Release Lever -- 5.99

Part Number 7616 -- 16 lb Cap w/o Pressure Release Lever -- 3.99

John

[Sea Hag]

Sent: 1/2/2005 10:41 AM

The dodger MH parts catalog list the cap for M chassis # 3781 830  . this croses over to NAPA / Balkamp # BK 7031447  16 lb Pressure vented  $6.09 . I Installed a Pair of  Stant brand caps 16lb pressure vented Stant # 11231 I belive they were about $6.00  or so @ . they fit and operate well . Neither type have a pressure release handle nor did the originals .  the original caps still worked but the rubber seal deteriorated causing  small pressure leaks . Sea Hag

[Rick Shaw]

Sent: 1/2/2005 11:22 AM

Dave,
Sometimes the pressure built up inside the engines is just a little too much for the system.   This happens all the time in older vehicles.   There is a seal in the radiator cap that wears out.   What you should do is to look for a 7 pound radiator cap.   Actually you should get both of them.   This will allow only 7 pounds of pressure to build up inside your system.  This saves a lot of wear and tear on the cap also.   Most of these systems were built to withstand 13 to 15 pounds of pressure when they were new.
Rick

[mightybooboo]

Sent: 1/2/2005 1:38 PM

Dont forget those radiator overflows,absolutely needed on these hot running old trucks.
BooBoo

[Sea Hag]

Sent: 1/4/2005 11:02 AM

I agree with Boo Boo , the expantion tank is very important on these engines cooling systems . As a full , air free  cooling system is essential to keep the temps down . . I'd suggest replaceing the caps with the 16lb type , and make sure the hose for the overflo is intact and not dry rotted . Sea Hag

[Beatty1950]

Sent: 1/4/2005 6:53 PM

Thanks ...

I installed a new overflow bottle on MissTank 6 months ago.  I used the old rubber overflow hose to hook it up (lazy).  I will check out the rubber hose and may replace with plastic transparent hose to see better what is going on.  Rubber hose maybe plugged which could explain the issue.  I will also replace both radiator caps with 16PSI model suggested.

Great to something to work on.  Nothing to do on my backup RV (83 FC35SB Wanderlodge).  I love them both.
 
Dave Beatty

[Beatty1950]

Sent: 1/8/2005 11:11 AM

As Suggested by John (HeavyHaulTrucker), I replaced both Radiator caps with

AUTOZONE Part Number 7816 -- 16 lb Cap w/ Pressure Release Lever -- $5.99

Problem solved thanks to the amazing set of expert help available from this valueable website.

Another item to add to my growing list of upgrades to MissTank.

Dave Beatty

[OldEdBrady]

Sent: 3/27/2005 9:47 PM

My '77 also has two caps.  I cannot say whether they are installed correctly or not, but I've had no problems.

The back cap is one of those "sealed" things for the overflow tank.  The front one is one of the levered ones.

As I said, no problems. so far. 

I'd look at the pressure ratings on the caps that are installed, and replace them with the same ratings.

[The_Handier_Man1]

Sent: 12/15/2007 8:24 PM

I don't know why some things work fine one day and not so good the next,  kind of like my brain, but today I learned something about radiator caps.  Now the radiator in my '73 D22I with a 440 has 2 caps.  I replaced them a couple of years ago, probably after the recore.  Anyway the pressure release one was on the extention spout and it started leaking.  I tried to release the pressure but it didn't let anything out.  After spraying coolant all around I switched caps.  Would you belive that it you put the press release cap on the top of the radiator, and you raise the lever, it releases the coolant into the overflow tank.  Talk about a light going on.  Just thought you would like to know this,  Les

[bluebird]

Sent: 12/16/2007 9:19 PM

Some differance on the lb cap  is where you are located geograficly. An engine would be able to run hotter than 212 degrees with a 16lb cap opposed to a 7lb cap. Cooling systems work just like a pressure cooker. Raise the pressure and you raise the working temp of the cooling system. If you don't run a cap or a very low pressure cap the system will boil over a little over 212 degrees at sea level.

Chuck

[ClydesdaleKevin]

Sent: 12/17/2007 7:17 AM

From my experience with the Ark, which had a 413 and 2 radiator caps, only one cap has to be a proper pressure cap...whichever cap has the overflow port with the overflow hose coming out of the neck.  Before we recored the radiator in the Ark, both caps had a port for the overflow coming out of the neck.  When the shop recored it, they blocked up the one on the top of the radiator, so only one cap had to be a pressure cap...the one on the front of the radiator.  The shop said 2 was overkill, and it was impossible to reach the top cap on the Ark anyways.

Kev

[DaveVA78Chieftain]

Sent: 12/17/2007 12:16 PM

Ahh, by design, the cap on top of the radiator is designed to be used for pressure relief.  It may have a coolant recovery system installed or just an overflow hose (year dependent).  The cap on the extension hose (front of radiator) is nothing more than a convience to the operator for filling the tank and typically does not have an overflow port.  So, if you want to release pressure (hot engine) you should have a lever type cap on the top of the radiator.    Dodge started using a 16 lb system in 73 with the RM300 and later models.  Prior to that, they used a 7 lb system.  Using a 16 lb cap on a system designed for 7 lbs could be asking for problems.

[vacuumbed]

My 78 M600 had the 7816 lever cap on the radiator extension. It was looking old so I replaced it with part number 7616 from O'reilly auto parts. Now it leaks everywhere I go when I park the RV. Should I have gone with the lever cap or maybe one from NAPA?

[Stripe]

Look at the pressure ratings(New and Old should match, otherwise you will have problems) and also make sure the seal is seating correctly..

[DaveVA78Chieftain]

78 would use a 16lb cap.  Both the ones you listed are 16lb.  Sounds more like you may not be getting it completely closed.  Do you have the regular overflow cap on the radiator?

[vacuumbed]

The radiator is a standard cap, while the extension was a lever cap. I did replace it with a 16 lb cap made by Murray. It is seated correctly but I don't know how good of quality the Murray cap is. I'm thinking of going with a NAPA cap, but I'm not sure if I should do the lever type like the one that was on there.

[DaveVA78Chieftain]

Lever type is used when there is an overflow connection so the fluid has somewhere to go.  Overflow connection is on radiator portion, not extension so the lever is of no real value.

[vacuumbed]

That makes perfect sense, thank you for the clarification on that Dave.

Here is what I have found so far. I stopped by NAPA this morning and picked up a 703-1699 radiator cap. It is a Balkamp made by Stant and it is 16 lbs.

The one from O'reilly is a Murray with MOTO-RAD stamped on it. The pressure rating is not confirmed, but it has the characters 16V stamped on the top.

Comparing the two side by side here are my observations:

The holding tabs on the cap lid are longer and of thicker metal on the Stant cap.
It may be possible that the shorter tabs on the MOTO-RAD cap may allow it to rock back and forth breaking the seal, but this is not confirmed.

The spring loaded sealing base of the cap has a significant amount of play in the MOTO-RAD cap as compared to the Stant cap which has only a little play.

For those two reasons, the Stant cap appears to be of higher quality.

[vacuumbed]

I installed the NAPA cap last night and took the coach for a 28 mile drive and NO leaks!

Final summary: Avoid radiator caps from Auto Zone and O'reilly for your coach. Get a Stant or a NAPA cap which is made by Stant for your coach. This part number for the NAPA cap that I bought is 703-1699. It is the correct 16 lbs. rating.

[DaveVA78Chieftain]

Thanks for the info.

[vacuumbed]

Follow up.

Drove the RV from Salt Lake City to Reno and no leaks with the NAPA/Stant cap.