Tried to order the O rings from Rock Auto. They only had one in stock. So I called the local chevy dealer. He had acouple of the O rings he could get another in a day or two. He swore the 15-1534066 O rings were the same ones that come on the coolant elboows. Okay, I said, give me the genuine gm coolant elbows. They were 17.50 a pair. I took them home and set them side by side with the Dorman elbows I had been getting from Advanced. I measured them with a micrometer and a dial caliper. Best I could tell the elbows were the same size, If anything the gm part was 2 or 3 thousandths smaller. Its really hard to measure the thickness of the rubber O ring. Best I could tell they were both around .103". In handling them I did notice that the gm O ring appears to be a black rubber O ring with an orange coating on it. The Dorman part appears to be made from orange rubber with no coating. I am thinking about waiting a couple days and see if Rock Auto gets more of thge O rings in inventory. I would like to see for sure if the 15-1534066 part is identicle to the ones that came on the GM elbows.

Ok. I got the "O" rings from Rock Auto. They look identical to the ones that came on the Geniune GM coolant elbows. They do not appear to be any thicker than either the Dormans or the GM "O" rings that come on the elbows. I took the tensioner off and cleaned and checked the openings real closely. Both elbows appeared to be a true 90 degrees with no distortion. There was some material that lookd like varnish on a couple of the openings. I scraped that away with a small screwdriver and clened them up with a coarse scotchbrite pad untill they were bright and shiny inside. I installed the Genuine GM coolant elbows with vaseline and put it all back together very carefully. It seems to be sealed up fine now. Time will tell.

I am having the same problem on my 1998 Olds 3.8 . The coolant elbow was replaced about a year ago and was fine until recently . It appears to be leaking (slight seapage) on the LIM side. I guess that I will get another Dorman elbow and try to find a slightly larger ("fatter") o-ring at NAPA . As far as RTV , I was under the impression that one doesn't use sealants with o-rings . If the RTV (has to bed red variety ?) makes to a better seal then fine . I'll do whatever work so I will watch this thread for a couple of weeks . - Thanks

I did my UIM/LIM recently, and I used the Dorman HELP elbow, within a day or two I had a small leak.
So I took the elbow back out and the o rings had melted a bit, that or the heat just flattened them out a bit.
I had gotten a Fel-PRO LIM Kit and noticed the Dorman o rings looked a little smaller than the Fel-PRO'*, but I thought nothing of it and used them anyway.

All I did to fix it was remove the elbow and put the Fel-PRO o-rings on, and I have not had a leak yet.
There is actually a thread somewhere where a guy measured the o rings and showed pics of the measurements, the Dorman O Rings were a tad smaller than OE ones.

RTV should not be needed if you use good o rings and not the Dorman ones, but if you already use RTV and have good results then I guess I'd not change anything.

RE: Lower elbow (tensioner to LIM ) - On my 1998 Olds I vaguely recall that the diameter LIM bore was slightly larger than the serpentine belt tensioner assembly bore (y/n ?) If it is what GM part#?

Does anyone know what std orig sizes these are ?

- Thanks

WilliamE- Were the Fel-Pro o-ring black ? (or orange etc)

- Thanks

The two Fel-PRO o-rings were orange, but the coating rubbed off a tad so I could see they were black but orange coated, I got mine with the FEL-PRO Kit - Part # MS98014T
There is a black one that also comes with the Fel-PRO LIM kit, it is for aluminum nipple on the belt tensioner assembly, my black o-ring with the Fel-PRO kit seemed a little too loose to use, so I just used the purple one that came off of the other coolant elbow that comes with the Dorman HELP elbow pack, it has not leaked...

I forgot to mention I noticed the Dorman o-rings felt stiffer than the Fel-PRO ones, not sure if that has anything to do with why they seem to fail.
I also could tell the Dorman o-ring was a little bit smaller than the Fel-PRO one, I wish I had a digital caliper to measure, but I did not.

Fel-PRO o-ring is on the left in each pic, in the first pic the Dorman looks bigger, it was the way I had it on my finger...



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The AC Delco'* mentioned allgeier look just like the Fel-PRO ones, I wouldn't be surprised if they originate from the same manufacturer...
I may pick me up a pack of them in case I ever change my tensioner assembly.

FWIW- I contacted Dorman tech support about the bad coolant elbows. They told me that there was a problem but were not specific about it (didn't mention o-rings and I forgot to ask). They told me that the "improved" version has production code number of 11300 or higher stamped on the elbow