The one that seals the outside edge of the radiator neck or the one inside?

 

The rubber washer is added to the bottom sealing surface of the radiator neck. The dimension that I think in incorrect is the flange at the top sealing surface. I don't believe it is pulling the entire cap down far enough. It is sealing the top surface just fine. There is no real increase in pressure at the top sealing surface because the overflow tube connection is between the top and bottom seals and diverts any coolant or steam pressure to basically atmospheric pressure in the overflow reservoir.

 

Continuation of post: Hypothesis and proof: Aftermarket radiator fill tube slightly too long (Duralast in this case) Observations: Drove 3000 miles at 75 mph no fluid loss. Idled parked for hours during trip with zero coolant loss. Concluded problem must be related to city driving. If AC is on, coolant fan is on. Compared six potential 16-psi radiator caps from different stores and all were same length from top seal to bottom seal. Coolant fan is designed to turn on when coolant temperature reaches 219 degrees. 16 PSI prevents coolant boiling to 220 degrees. In stop and go driving engine temperature can get in the range of 212 to 219 degrees. If the vehicle is turned off in this condition (stop and go traffic then parked) the pressure cap should prevent boiling, but if it isn't holding 16 PSI for any reason it can boil add too much coolant to the reservoir, sometimes even in the physical state of steam bubbles rather than hot water. This can happen if the radiator cap doesn't press firmly enough against the bottom seal to compress the spring all the way into its proper tension to regulate the pressure properly. Occassionally after such driving and parking I could hear the boil and sputter as the heat from the block and head moved into the coolant. It would last a few minutes and even spurt water out the reservoir overflow port. I installedvthe aftermarket radiator during a breakdown in Montana and it drove and tested fine. No hot city driving in rural Montana. I didn't see ir drive the van for the next three years. When I did they were carrying coolant in the van to top off coolant level in the reservoir. I took possession of the van and replaced the radiator cap but immediatelt took it back into the store because it didn't feel tight enough (Factory cap looked good but replaced with a Duralast cap that should have matched Duralast radiator) so I exchanged it brand new for a pressure release duralast cap with lever that I could feel more spring pressure against the bottm seal. Someone else in Las Vegas drove the van for six months. When I took possession of the van again they had a half empty bottle of coolant in the van and had been using it to top off the reservoir when it got empty. They only drove in the city. That's when I took possession again, drove it 3000 miles home, measured different new caps, bought washer, etc. We have a 1/4-mile steep hill into our rural community. So steep that concrete trucks can only carry 9-yards of concrete up the hill or ut will spill out the back onto the pavement for 1/8th mile of the steepest part. I simulated city driving by driving at slow speed in low gear up the steep part in the right lane, coasting back and repeating the process two more times and pulling off at the top of the hill, and turning the engine off. With the added rubber washer no boiling because the extra 1/8-inch of rubber compressed the spring into its pressure regulation range. I took it out and repeated the climb and turn-off and in boiled. I reinserted the rubber washer and the climb. No boiling! Problem solved. I believe the overall length of the aftermarket radiator is within specs but the top flange is slightly shorter resulting in slighyly longer distance between the sealing surfaces becausevthe latch is chtching slightly higher. Many aftermarket radiators are manufactured by the same company and rebranded for different stores. I suspect that some could even show up in the dealerships. I also expect the problem could exist across different generations of Mopar minivans because I have seen similar posts of the problem but no one solving it with a rubber spacer as the conversation often leads to leaking checking for leaking overflow tubes, leaking reservoir, replacing headgaskets, etc. Mine is 3.8L 2008 T&C.

 

This is very interesting because my van does not over heats but the darn engine bay gets so hot during the summer that u cant even touch the hoods van.

Actually this post grabbed my attention because i always thought since i got this van last year (2009 4l dgc sxt) that the radiator cap looks ok but doesnt feel like closing tight as the original poster says. BTW I never had the issue of coolant disappearing.

In a 2006 van i had,had to actually push down the cap to release it.

Would you please post a picture of the set up with the washer??? Do you glue it???

Thanks

 

I'll try to take a meaningful picture and post it. No glue was used or needed. The rubber fender washer sits on the base of the filler neck and the similar rubber washer fastenened to the bottom of the radiator cap applys pressure to it all the way around. It doesn't try to fall into the radiator when the cap is removed, and didn't stick to try the radiator cap when it was removed, yet. Note that you will lose no coolant because you idle for long periods with the AC on because the fans are running if the AC is on, or if you are cruising at more than about 30 MPH. It only loses coolant if you drive in stop and go traffic at slow speeds and then park the car so the block and head heat transfers to the coolant for a few minutes.

 

This was a very interesting read.

What a great contribution to the forum.

If anybody else in the same situation, follows this suggestion and has positive results, please return, thank the originating member, and substantiate the SOLUTION, please

Thank you in advance and thank you rednopnolyag

 

Hi, hopefully you'll see this. I've been having a similar problem with an emptying reservoir. Can you better describe the size of the neoprene washer?

 

I can. I Actually stopped by ACE Hardware yesterday and took the attached picture from the pull out drawers on the shelf in their Fastener Isle. They are neoprene (rubber) washers. I placed the size washer I used on top of the box in the image. It is 1 1/2-inch OD by 1/4-inch ID by 1/8-inch thick. They are 65-cents so I bought two in case it needed to be spaced more but I only used one because it resolved the issue. The 1 1/2-inch diameter washer matched the washer size on the bottom of my radiator cap and lay nicely into the bottom flange. The 1/4-inch in the bottom worked just fine with the center brad that held the factory washer to the bottom of the radiator cap. You are not trying to seal that center hole with the spacer washer in the image. It is only a spacer to compress the spring a bit more so it works correctly. Just lay the washer in the bottom of the neck. I put a little coolant on mine for lubrication purposes so the washer didn't wrinkle during tightening, but it probably wasn't necessary. If you can drive about ten MPH up a long hill with the AC off (Turning the AC on automatically turns the cooling fan on and cools the radiator), and stop safely at the top of the hill and shut the van off. I made onetrip up, backed down and made another trip up before checking. Not all hills are the same. I live in rural Alabama so there was no traffic during my test, and the right lane just happened to end with a place to pull off at the top of the hill. I got out of the vehicle and verified the bubbling sound was coming through the overflow canister. After it cooled I placed the spacer and did it again to verify the fix. Then I took the washer out and and verified that the problem returned. Then I put the washer back in and verified the fix again. It has been about ten months and the problem has not returned. PLEASE ALLOW ENGINE TO COOL BEFORE REMOVING RADIATOR CAP EACH TIME! I stopped and cooled my radiator down with the water hose each time. I was lucky because my shop is only about 1/4 mile from the top of the 1/4-mile long steep hill I used for testing. It's nice to have a memory of the one time in life I was actually lucky 😃 Good luck to you.

 

He hasn't posted inn years. But from what I get from his post he basically matched a washer to the bottom of the radiator cap. The center needs to have space for the pop valve in the center of the cap, and the outside needs to go out as far as the edge of the cap. Essentially he made the cap's bottom gasket thicker, but just put it under and not on the cap.

 

Thanks I'll give it a try.

PS> I saw a post from him earlier in Feb.

 

He hasn't posted inn years. But from what I get from his post he basically matched a washer to the bottom of the radiator cap. The center needs to have space for the pop valve in the center of the cap, and the outside needs to go out as far as the edge of the cap. Essentially he made the cap's bottom gasket thicker, but just put it under and not on the cap.

The rubber fender washer I used is 3/16" (hole), 1 1/2" (wide), 1/16" thick and pretty much fills the fill hole. The DGC is a 2003 and seems to lose 1/4 to 1/2 gallon every few weeks. It doesn't over heat but it briefly when I lost coolant with a broken heater hose a few years back. I stopped immediately. I think this problem started well after that. It seems like I get a little coolant in a small depression in the corner near the head but nothing substantial. One friend suggested to have the head bolts torqued. The oil is fine and nothing seems to be coming out the exhaust, so hopefully this does the trick

 

That 3/16 center hole concerns me as the center is where the reservoir suction valve is located.

Also, I wonder how the application of this additional rubber 'spacer' fender washer affects the cap's PSI rating.
It is all about the spring pressure on the outer lip of the inner radiator throat. Adding thickness to overcome the aftermarket variation in manufacture, understood.

But what is the new system PSI and could that be excessive to the point of causing a leak at the head as you describe?
We are looking for 16-18 psi (just over 1 atm)