Wrong Radiator Cap?

I have a 97 Cherokee 4.0 and yesterday I had a new radiator installed. The bottom tank had seperated on my original which lasted 150k so I guess I can't complain.

Anyway, I noticed they put a 13 psi radiator cap on it. For some reason I thought I had read here before that it was supposed to be higher than that. I searched but couldn't really find anything. From what I could find searching different parts places online, I think it's supposed to have a 16 psi cap.

How much of a difference is this going to make? I'm planning on taking this thing off-road Sunday but if I can wait until Monday I'm sure they'll swap me for the correct cap.

Good question. I installed a CSF Radiator about a month ago and tried to use the old cap but it leaked a bit under pressure. I went to the local auto parts store and they had only 2 options for me (normal or pressure relief). I went with the normal but there was no spec. for psi. The other just had a bleeder lever that could be flipped open to relieve pressure if needed. Mines been perfect. I'll go see if I can find any psi rating on the cap.

The open system uses a 16 lb and teh closed used a 13lb cap so I thin you are ok. The reason your radiator tank blew off is because of trapped air in the system.

xjnation said:

The open system uses a 16 lb and teh closed used a 13lb cap so I thin you are ok.

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I have a 1997 which is the open system, so my 13 lb cap would be wrong. What difference will this make if any?

IdeaMan said:

I have a 1997 so which is the open system, sooo my 13 lb cap would be wrong. What difference will this make if any?

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yes you should have the 16lb sorry for teh missread of year been up all night doing taxes after a harddrive crash. the difference is when it opens to let fliud travel to the over flow. 3lbs is substancial. pick up one anywhere for like 4.99

I've wondered about this too, I upgraded from a single row OEM to a 2 row Modine and I'm still using the OEM 16lb cap. Its still the same cap for the two row right?

The cooling systems are pressurized to raise the boiling point of the coolant. Rule of thumb is 3*F for each pound of pressure.

Theoretically, a good working system with straight H2O and a 13# cap would have a boiling point of 251*F and with a 16# cap would have a boiling point of 260*F.

The newer engines are designed to run hotter for emission control.

I would keep the 16# OEM cap upgrading from a single row to a two row.

Tom

Thats what I thought but I figured it was worth asking. Thanks

OK, this all makes sense, but I still don't understand why all of the parts stores I have checked (NAPA, CSK, Autozone, Carquest, etc.) only list the 13 lb. cap for the '91 on up "open" system. My '93 had a 16 lb. cap on it when I decided to upgraded the radiator. The dealers in Utah don't normally stock the OEM cap because there is so little demand for it. And why haven't other regulars in-the-know chimed-in here with all of their OEM/cooling system knowledge? There is almost no available specific information to be searched for and had here. I myself will be calling the dealers back or perhaps even someone at the factory until I get to the bottom of this.

That way they can sell you more parts when it keeps overheating LOL... Buy them at the dealer....same with the thermostat too...

Crawler,

Yesterday on the trail over lunch the topic of those in the know not posting to tech came up or why don't more people post to the tech boards anymore. One of the guys is a respected member who has posted many times, he works for a Jeep dealership. He gave me these two answers.

1. Someone already posted the correct answer.
2. Someone already posts the correct answer and the OP doesn't believe it or won't follow the advice or wants to argue.

Goatman wrote something along the same lines in the members section a week or two ago. Crash finally placed a gear thread sticky because he got tired of seeing the same questions about ratios and tire size over and over and over.

So to answer your question about why someone in the know hasn't posted. The above states it pretty clearly.

Tom

Boatwrench said:

Crawler,

Yesterday on the trail over lunch the topic of those in the know not posting to tech came up or why don't more people post to the tech boards anymore. One of the guys is a respected member who has posted many times, he works for a Jeep dealership. He gave me these two answers.

1. Someone already posted the correct answer.
2. Someone already posts the correct answer and the OP doesn't believe it or won't follow the advice or wants to argue.

Goatman wrote something along the same lines in the members section a week or two ago. Crash finally placed a gear thread sticky because he got tired of seeing the same questions about ratios and tire size over and over and over.

So to answer your question about why someone in the know hasn't posted. The above states it pretty clearly.

Tom

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Dear Mr. "Boatwrench"...

OK, alright, I can see YOUR point. But only in as much that it has already been posted to buy the factory cap. While it may indeed be the best advice, what is wrong with asking the reasons why?

Nobody, including "Martin" (who has sworn by OEM caps, stats, and hoses more than anybody else I have seen in my hours of using the "Search" function) has been able to answer the question of what the factory cap for the open system is rated (he openly admitting he didn't know).

I tried using a brand-new aftermarket 16 lb. cap on my new radiator (replacing the 16 lb. cap that was on the old radiator) and it immediately leaked. I put the recommended aftermarket 13 lb. cap on and no problem.

If I need to be using a 16 lb. cap, then that is what I want to use...

But the dealers didn't stock the OEM caps because of the low demand, and everyone else in the aftermarket was saying and offering something else (I appreciated RichP's humorous response as to why)...

And NOBODY that had the technical answer cared to set the record straight for the rest of us (an answer that YOU "pretty clearly" state has already been discussed, but in reality is NOT available through doing a "Search")...

THAT is MY point, the one you obviously didn't get the first time... ;^]

Now, just so you'll know I can take a hint, tomorrow when I go pay for my "special order" OEM cap in advance (which will take up to a week to receive) I'll do my best to get a pressure rating from one of the parts guys behind the counter. They'll probably tell me they need a VIN # (LOL). If they don't know, I'll ask to speak to one of the techs. If I'm still not satisfied, I'll go so far as to call corporate in search of such deep, dark secrets. When I finally get the answer (and I WILL get it) I will be happy to post it here for the rest to see, that it may then be archived, and you will truly have an excuse to try and make someone else feel sorry for asking such a reasonable and pertinent technical question.

Nightie-night... ;^]

See #2 in my second post.

Rich P may have been humorous but held a lot of truth of the "why" part houses only stock 13# caps. amplifying info: Parts houses stock many generic parts, some close enough to specs, but not exact. Floyd at the local NAPA can't be expected to have every exact part for every make and model of vehicle because that would be to costly, likewise that's why when you go to the dealer a part may have been superseced (sic?) by another similair, but not quite exact part.

With your 16# cap...what leaked? the cap-defective...the radiator? - weak because the spec engraved on the cap is a typical not exact opening pressure and when pressure testing systems usually use 3-5#s greater than designed operating pressure.

The original question "which cap to use" had been answered. Ideaman should be using a 16# cap. Your question of why some of the regular in-the-know folks haven't posted I answered with a logical guess based on a discussion with a few of the "regulars". and my post which when read makes it pretty clear (see reason #2). The answer to Ideaman's post was provided, RichP answer to your post albeit tongue in cheek maybe..was answered. your question about why some people aren't rogering up was answered.

But if it really wound your panties in a knot here's some technical stuff, which in your post was not a question, but a statement. I only have four FSMs in my garage, 77CJ, 79 Chevy Truck, 89 Jeep and 2000 Jeep. I gleaned these gems from the latter two.


89w/o pressure bottle 12-16psi
From a 1989 FSM....
"the cap contains a spring-loaded pressure relief valve that opens when system pressure reaches the release range of 83-110kPa (12-16psi).

89 w/ pressure bottle 16-18psi
From 1989 FSM...
"the pressure bottle is equipped with a pressure cap which releases pressure at some point within a range of 110 kPa (16-18psi).

2000 cooling system 14-18psi
from 2000 FSM...
"All radiators are equipped with a pressure cap. This cap releases pressure at some point within a range of 83-110kPa (12-16psi). The pressure relief point (in pounds) is engravde on top of cap."

Now knowing that the higher psi rated cap would raise the boiling point in the cooling system, I would use the 16# cap AFTER pressure testing the system at 18#s to check for leaks.

I didn't think my second posting was dripping with venom, if you took it that way, oh well not much I can do and that's a problem with this form of one dimensional communication. If you think this post has venom, well yeah, it was written with a little higher blood pressure.

Good Luck,
Tom

Mopar part numer for the pressure cap is 1-52079880AA, 16PSI, got one sitting here in the bag, Need the thermostat part number ? Here it is anyway52028186-AB marked 195F got one of those in the bag too.

I called the radiator shop that put in my new radiator. They told me they only put 16 lb caps on "newer" vehicles and put 13 lb caps on everything else. They have a lifetime warranty on the radiator and if I put a 16 lb cap on, I void the warranty. Should I keep the 13 or go to the 16?

IdeaMan said:

I called the radiator shop that put in my new radiator. They told me they only put 16 lb caps on "newer" vehicles and put 13 lb caps on everything else. They have a lifetime warranty on the radiator and if I put a 16 lb cap on, I void the warranty. Should I keep the 13 or go to the 16?

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Its a NEW radiator,what has the year of the vehicle got to do with it.Warrenty is only on the rad and not hoses and such.
Put the #16 on and forget it.
Wayne

ok guys, not to hijack thread but it looks like its pretty much finished. my 93's radiator cap has started leaking a little bit. i went to the parts store and they only have the 13 lb cap. is this what i should be running? i have a gdi radiator if that makes a difference. thanks

"Boatwrench"...

You were the unfortunate recipient of a bit of frustration on my part for not being able to find the information on my own. It wasn't my wish or intent to argue, I only wanted to come up with the bottom line supported by facts and /or numbers, and not just opinions. This is indeed the very first thread that I know of where the actual "data" has been presented. On behalf of those seeking and that are yet to seek the answer I'd like to thank both you and "RichP" for helping to set the record straight.

Now, let me tell you a little bit about today's adventure...

I went ahead and ordered my OEM cap like I said I was going to ($10.++). I was correct, the guys behind the parts counter at the dealer didn't have a clue as to what the caps were rated and couldn't find the information to save their lives. And to my greater disappointment, neither could the two people I talked to in the service department. When I got home, I called corporate in MI and was put on hold for 15 minutes. When I finally got to talk to somebody, I was again put on hold for another 5 minutes while they researched an answer for me. The answer I was finally given was this:

"The radiator cap for the '93 XJ open cooling system is rated for between 12 and 16 psi, and will be stamped as such upon the top of the cap."

That's when I decided it was time to give up. My cap is being shipped-in from 200 miles away and is the only one available in the entire State of Utah. I sure hope it says 16 lbs. like "RichP" says... (chuckle-chuckle)

Thanks again guys, I really mean that; both for the definitive answers as well as putting up with me... ;^]

Crawler,

I never expected my name to appear in your post. I have posted the same thing over and over but the answers I give are formed my the experience of working on my 88 XJ with the closed system AND my professional career as an engineer. I deal with aviation items and spending more for a known good item is a no brainer for me, but right now my income vs outgo is such that I can spend the meney on the parts I prefer. I was in college with no money I might do things different and chance a break down.

The close coolling system on my 88 XJ uses a strange "radiator cap" on the pressure bottle and I have NEVER found the cap available other than from the dealer. I carry a spare dealer cap in my vehicle just in case I need one on the weekend when I am at the corner of Boone & Docks lol

On the use of hoses I have used Goodyear and I used dealer. The dealer were the better made items. The rating of the radiator cap for your XJ is beyond my experience since I have a closed cooling system. I hope you get a cap that works and if you over heated I recommend you change the thermostat. I also learned that hard way to change Cap & thermostat after an overheat. IF I overhead again I'll change both as "best practices" maintenance.

Thanks Martin...

I have appreciated reading the input of people such a yourself, Eagle, RichP, Dr. Dyno, GoJeep, etc.

I just found it a little perplexing that after all that has been posted on XJ cooling problem issues, hard numbers related to the open system radiator cap have appeared to be so speculative. The t-stat, fan clutch, radiator, hoses, coolant, etc. all appear to be hashed-out to the point that even doing a lazy man's search should get you the answers you seek. But why not the radiator cap?

Oh sure, there's a lot of "use the OEM cap" to be found, But until now, and contrary to what has been claimed, no archived post has ever offered up a part # or data related to PSI. Helpfull speculation, authoritative ego, and the voice of experience has claimed that 16 psi is the pressure we seek, yet you cannot just walk up to the OEM parts counter, ask for, and recieve it based on year, make, model, and displacement.

Today I finally found out why...

I received a call from the dealer that I had ordered my OEM radiator cap from. It had arrived in only one day from 200 miles away. The first thing I did was compare the part # on the box to the one recently given for the 16 lb. cap. They did not match. OK, so maybe it was a superceding #, so I took the cap out of the box. The stamp on the top of the cap said: "14 lbs."

I had gone ahead and followed the advice that was given, to get the OEM cap, one of the main and only reasons given being because it was the correct pressure rating at 16 lbs. What the hell is wrong with this picture?

The OEM parts counter guys assured me it was the correct cap for the open cooling system. I then gave them the part # recently given for the 16 lb. cap and asked for availability and application. They had two of them in stock, and said that it fit a number of different applications, but that the open system L6 242 4.0 WAS NOT listed among them. Great, now what's a "mother" to do? I am in total agreement with the logic behind using the higher rated cap, but will it still work?

I asked them to hang on while I went out to my XJ and grabbed the old cap that was on the old radiator I had replaced (yeah, I hang on to that kind of stuff for a while, you just never know...). I handed it over to the parts counter guy and he found a # on it that he then entered into the system. As it turned out, the # was the older # for the current 16 lb. cap # and when physically compared appeared to be interchangable. They offered to let me have the 16 lb. cap in place of the 14 lb. one they had ordered for me, so I took it. It later fit and although too early to tell for sure appears to be working well so far.

So, what have we learned here?...

I don't know about anyone else, but I've learned that according to Mopar, the current correct pressure rating for the OEM XJ open style cooling system radiator cap is 14 psi, and that is the rating of the cap you will recieve. The 16 psi cap will apparently work, but is not listed as an option and you will have to ask for it by specific part #. Still unknown (to me, anyway) is if that the rating spec has changed somewhere over the years and why (I would almost feel safe to assume that it has based on few different factors). But this is way it is and was as of today.

I'm usually not nearly this anal-compulsive, but just felt that with all the problems we face in properly maintaining and operating the cooling system in this "righteous ride" (especially out here in the western deserts), every last little bit of capacity you can squeeze out and fine tune helps, adds up and will hopefully be there for you when you need it the most.

Peace everybody... out.