Chevy and GMC Duramax Diesel Forum banner

O-ring Under Thermostat Housing

20K views 2 replies 2 participants last post by  jsh101 
#1 ·
Hey guys,
I put a new water pump in the LLY (first timer, and Im no pro), everything went pretty well untill I filled it back up and water started running out of the bottom of the thermostat housing where the pipe down to the water pump goes in. Looks like I must have damaged that o-ring, which I guess isn't a big supprise cause it was a pain to get that pipe back in there. I started to pull it back apart, and I'm having trouble with that. I can't get the wiring harness that goes through the fan pulley block back out to even pull that off. So I guess a few questions:

Does the fan pully need to come off to get that pipe off and back on? Looks like some people say yes and some say no, maybe depends on the year? I attched a picture of the (SOB) pipe in question, did not all years have that 3/8" hose that comes off of it that you get to fight at the same time as trying to get the o-ring to seat? I put a new 3/8" transmission oil hose on there which is pretty stiff, in hind sight that probably didn't help my efforts, but it's what I had.

If the pulley has to come off, how do I get the wiring harness that goes through it disconnected? Looks like different years used different connectors? I thought I got it last night by prying the tab from behind with a paint can opener but now I can't get it to disconnect. I attached a couple pictures of the harness, hopefully that helps.

Can I remove the pipe and replace the o-ring with the water pump installed, or do I need to pull the pump, replace the o-ring, put the pipe back in and then re-install the pump? Would that sequence be better?

Where do I get a new o-ring for the connection between this pipe and the bottom of the thermostat housing? The new one came with the pump, but I'm guessing I ruined it. I could put the old one back in but I'd hate to do that. No parts store that was open this afternoon had one, is it a dealer only item?

It's not an emergency, but I've been working on this for an hour or two while the kids nap and after bed time this weekend and Moday's coming quick.
Thanks in advance!
 

Attachments

See less See more
3
#2 ·
It's been a few years, but I wrote this while it was still fresh on my mind...

For some reason, I assumed I had to take out the bypass pipe. I think if you are careful not to disturb it much, you can unbolt and slide the water pump out. I removed mine (since I got a new o-ring with the Merchant water pump kit). Well, I had trouble getting the pipe back in and it leaked like crazy. I took it out and the o-ring was nicked in several places. Here's what worked for me:
- Of course, make sure the hole under the thermostat housing is clear of crud; mine was actually quite clean.
- Put the o-ring on the bypass tube and slide it all the way down to the bulge. This was my big mistake the first time; not seating it lets it move/roll/twist when you shove it in. I greased the hole and the area above the o-ring on the tube. But this time it slid in very easily/smoothly (unlike the first time). My original o-ring looked good so I re-used it after ruining the new one.
- NAPA sold me a foot of cheap 3/8" heater hose for the bypass tube to turbo line. This bothered me so much I went to a dealer the next day and bought a new hose (#94002821) that came from Japan (retail $23!! but I talked them into a $6 discount). It's obviously a much higher quality piece of hose and should easily last another 10 years.

On my first try it was difficult to push up the tube, and it destroyed the o-ring. On my second try, with lots of plumbing silicone grease on the tube and up in the hole, the tube with o-ring slid in, and twisted to line up, without any resistance. I suspect if there is any resistance, you're probably destroying the o-ring at that point.

There is a lip/bulge at the top of the tube, and then another about 1/2" lower, right? I positioned the o-ring in that 1/2" section, but all the way down against the lower lip/bulge (with no twists on the o-ring, of course). I pretty much filled the rest of the 1/2" section with silicone grease. I have no idea how much is too much, or too little.

I suspect, but cannot prove, that the o-ring actually seals in the tube against that lower lip/bulge, and that it really doesn't completely seat until there's pressure in the cooling system. When I filled with water and pressurized, a few drips came out (I think, but there tends to be water in that area when working on it) . . . and then any drips completely stopped.

Others have used Sil Glyde instead of the silicone grease I used. The stuff I used is probably a little less stiff (viscous) than petroleum jelly. Sil Glyde says it works for brakes, does that mean it's thick? It says it has a tough film, maybe too tough? I don't know. Have others used it successfully?

The o-ring I got from Merchant with the water pump kit looks exactly like the oem. Since I destroyed the new o-ring I re-used the old one. If there are differences, I couldn't tell. The old one has been in there for 3 years without any problems.

(Some duplication above because I actually responded to several posts on another forum. But look, I had more to say!!)

Electrical connector? I don't remember this. I think I removed the fan from the bracket, which was very difficult (I had to build a tool). Later I thought I might have been able to just remove the whole fan bracket. Maybe that's what you did? But now there's a pesky connector to disconnect before you can remove the bracket? Sorry, I can't help here. I seem to recall I had to take the fan pulley back off to get to that tube, but I'm not positive.

Water Pump Removal? No, you shouldn't have to take it off. The tube goes into the thermostat housing and rotates onto the top of the water pump. Again, when it's done right, it glides effortlessly into place. Otherwise, it destroys the o-ring.

On pressure testing: I suggest buying or making a pressure testing kit. I bought a 60psi gauge for swimming pools at Lowes, and assorted 1/4" T's, ball valves, converters to 1/2" hose barps (intended for pex), and an air hose quick connect. Turning the compressor pressure down to 20psi, I use one of the ball valves to gently pressurize the system (viewing the pressure gauge), then closing the valve and seeing if it holds pressure. Now I can test it without having the fan or belt on, and not wait for it to heat up, and not burn myself, and control/test the pressure easily. I just tap into one of the hose line (like the 1/2" that goes from the reservoir to the radiator).
 
#3 ·
Thanks Jake. I finally got it this week, I think the o-ring that came with the pump was the wrong one. Here is some additional info that I hope may help someone if they get in the same situation:
I think the fan pulley needs to come off, the release for that electrical connector is just squeeze it (left to right) on the front. Easy. Not sure how I missed that.
As for the o-ring, I found a U-tube video that said use a #116, 19.8" ID and 24.6" OD. I got one from NAPA on Sunday, it seemed really tight going over the pipe but it didn't leak, if you are in a pinch this would probably work.
I changed that o-ring with a GM part number 94051259, which is actually an injector o-ring and is red, sounds like a different material that is a little tougher.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top