LT1 Overheating, SOLVED.
 

So some of you may know that I've been fighting a high coolant temperature with this rise in ambient temperatures here in Southern AZ. I eventually overheated. Thinking this was a one time thing I re-bled the system and went about my business.

I was wrong. Ugh. The car overheated again on my next drive. I re-bled it again thinking maybe I did it wrong. No Bueno. So, thinking I did it wrong again I went to re-bleed it again and this time I revved the engine up to about 2K to really get it pumping to add more fluid and close the cap with a little more fluid in it. While revving I heard a whinning/grinding noise accompanied by a drop in coolant flow. Uh ohh. For the sound I heard see the video below, with the engine on and revved up it's a little hard to hear. Lucky for you guys the video is with the pump off.

I grabbed my handy dandy stethoscope and found the sound to be originating from the water pump. So I pulled the pump and found this.


The spline drive is P/N: 10128334 and only available at your local GM dealership (I paid $54 with a military discount for just that coupling) Argh! The water pump splines were also worn out so I got a cheapo Master Pro Water Pump and some new hoses too while I was at it. They didn't have any 160°F thermostats (and I got a lecture from the nice lady behind the counter about thermostats and how the 180° would be better on my car, she got a lecture about my car, LOL).


The temperatures didn't suddenly jump like a water pump failure, they gradually increased over the period of a couple weeks. So as the wear increased the more the spline drive slipped and the less the water pumped and the hotter the coolant temps got.

After repairs I took it for a test drive after it warmed up to about 165°, it's still 103°F OAT, and flogged on it decently. I got the coolant temps up to about 205°F where they pretty much peaked (with the AC on). I was only driving for about 10 minutes though. I then let it idle in my driveway for about 10 minutes. Usually, well for the past month or so, the coolant temps would rise in this scenario to about 220-230°. Not this time, this time they dropped from about 205° to about 190° before I shut it down, obviously satisfied with the results. This also tells me that the spline drive coupling had been slipping for quite some time now.

Our cars are getting old, this spline drive has 155K+ miles on it and is 20 years old, it's lasted over a year with my current build. I thought I'd share this with everyone else so you all too can keep an eye out for this as it could possibly be your issue one day (or currently). I do recommend that everyone go get one of these couplings and keep it in your glove box as we don't know when they'll stop making the coupling and they are already very hard to find. I got lucky and found 1 in a local dealership so I was able to repair it same day instead of waiting on shipping.

Some grease and good o-rings on the splines should also help longevity.

LT1 Overheating, SOLVED.
 

Did the grease, didn't see any o-rings.

o-rings stop dirt from getting in and grease from getting out.

LT1 Overheating, SOLVED.
 

Yeah I figured that. But I saw no provisions for o-rings. Is there a write up on that? None of the new parts came with o-rings.

Look at the bottom of the spline in the opening video screenshot. If you used a Felpro gasket kit bet you have the rings in a baggy of leftovers.

Ahh. Nope, I used the gaskets that came with the pump. Only the two water pump to block triangle two port gaskets. My old set up's didn't have them either. Arg!

Well, I'll throw some on when I get the upgraded radiator in a couple months. Thanks for the tip!

I meant a Felpro front cover or conversion gasket kit you probably got when building the motor.

The o-rings fit in the grooves in the engine driven spline and WP spline. The FelPro timing cover gasket kit (TCS 45953) includes the o-rings (FelPro p/n 407). I found that aircraft o-rings p/n M83248-1-012 fit perfectly and the price was right, maybe you can find some at your work. Use some Moly lube on the splines like a CSD/Gen.

LT1 Overheating, SOLVED.
 

Thanks for the part numbers, I bet I do have some of those! Yep, got the moly on there already.

Nice catch, I like how you post things for trying to help people having a problem that you always solve. I'll have to look out for this if my car gets hotter than it already is..I have noticed my cars temps have been climbing lately since the NC summer has kicked in. I couldn't imagine it where your at, AZ correct? It's gotta be hot enough to fry an egg on your T-top! Lol

Beware of cheapo parts store water pumps. One of the hose barbs came out of the aluminum housing of a Napa pump on my friend's Z after less than 500 miles. The press fit on it was very loose and filled with silicone. It was exchanged under warranty and the new pump has the same flaws (the barb could be rotated easily). It is from China and I think Delco sells a reboxed one in addition to the OEM design.

https://cimg2.ibsrv.net/gimg/ls1tech...2232061c6a.jpg

Yeah, some people make cookies in their cars on the dash for lunch time snacks. This is true actually. It's been over 110+ last week and this week is a little cooler at 105+. Pavement temps have been over 170°F and I'm sure with my all black glass top it's easily close to that (or maybe even higher??) inside my car without the shades on (I always use my shades).

I try to help where I can. I see a lot of threads where people ask about a problem, but rarely post their resolution. Trying to change that.

Eek! I'll definitely be wary of that. Mine didn't spin at all and no leaks so far. This one also said reman (so I'm assuming it's a stock rebuild), but interestingly there was no core charge. It's the only one they had in stock actually so time pressed me to get it done and get the cheapo unit.

The stock Delco should have PH-9000 or something like that cast into the front of it. At least it does on the one I gutted for my EWP.

Send it out to be gas nitrided!

Wow...I'm surprised yours lasted that long, same thing happened to my original WP back in the late 90's with only about 65K on my car.

#156. If you grease the coupling and don't use the o-rings, the grease will just capture any dirt and turn it into a grinding paste.

https://cimg7.ibsrv.net/gimg/ls1tech...d5e05349c6.jpg

Electric waterpump = win

Never had an issue with mine, but good thing I'm in the middle of going to a EWP. Another failure point I won't have to worry about. I'm putting a Griffin radiator + EWP
on now because of overheating due to a horribly clogged stock radiator.

Good post and thanks for sharing.

Not always. I wouldn't trust one in my driving condition. Try the electric water pump on a road course, no win there. When customers show their coolant temps rise on the highway, that tells you something about the pumps limited cooling capacity. Plus how many EWP have gone 20+ years?