Kingtal0n

I did research first,
https://www.nookandtranny.com/Info_LSx.php#LSWaterPump


they flat out tell you, 97-04 is an integrated thermostat housing for LS1 style water pumps.


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I take my water pump off, its an LS1 style integrated thermostat in there. K


So I go to the local part store, and I see the thermostat on the left:


The one on the left is what they have for sale, Where as mine looked like the one on the right.

Not thinking anything of the difference (there is only 1 kind of integrated thermostat...? ) I bought it and put it in. Engine overheats immediately 240*F within minutes.

So there is a difference between them. I watch a video online and it looks like that end part needs to plug the hole under it in order to send water to the radiator. They are different shapes (one is flat) so I guess this is why...

So here is my question(s):
1. Why does nobody mention there are 2 different kinds of thermostats for integrated LS1 style pumps?
2. How do I tell which water pumps they sell (out of the 10 different brands) are using which thermostat housing? I want to buy a Gates pump but it doesn't come with housing and there is no mention of casting number.


Final info:
The thermostat on the right says:
DORMAN 902700 {#12571261, 8125712610} Info
w/Water Pump Casting No. 12562459;

Notice there is a special pump casting number associated with the weird shape thermostat. I tried to find a 160*F unit for that casting number but there is nothing.

Robrote

First off, I would never put a Doorman product on my Vette. I bought a T housing for my vette ( I think it was gates), it was integrated. No issues. They are either selling you the wrong item or it's packaged wrong.

Kingtal0n

I am new to the LS platform so making mistakes... yes many leftover parts I didn't need are piling up.

I just made the connection that the casting # is designating ls1 "old" style, I think.

Which means my 'original water pump's' t-stat is different some way, that is not consistent with what is commercially available.

I bought a new gates pump and another T-stat, I will make some measurements between pumps, as I have a feeling that the pump on my engine now is different somehow (off-brand).

this is the pump on my engine now:
https://www.ebay.com/itm/Engine-Wate...5XtDKP&vxp=mtr

It came with it's own thermostat housing/thermostat, which is what I initially was drawn to. I think there is a difference in the design of T-stat though.

I am glad this happened. I need to change a plug in the heater core outlet from brass to a sunken aluminum (brass plug is ugly) and it just wasn't a priority. But now since I am getting a new pump...

Robrote

That pump appears to be the right one. It would be a good time to flush and fill, maybe bypass the throttle body, and do not forget to clean the front of the Rad and Condenser. They get loaded with debris on the corvettes. Get a soft bristle brush and make a long handle and clean it off good. You'll be shocked at the amount of dirt that you get out and the car will run so much cooler.

Kingtal0n

The plot thickens.

I went to the auto store and looked at their "duralast" water pump. They also had in stock both thermostats in the picture above, my original cup shaped and the other flat one.

I measured their "dorman" thermostat, it is identical to mine. So as far as my "off brand pump" it appears to use dorman style thermostat. I guess the chinese "copied" the dorman unit?

In either case. The thermostat looks like it would work, they both appear similarly able to block the hole. So this has become a little unclear, My next step however remains unchanged: i will be putting gates pump with flat style thermostat next.

6speedsteve

Did you burp your cooling system, usually when you overheat that fast you have air in the system.

gimp

Think about how a thermostat works: it starts to open as the fluid begins to rise to the correct temperature.

So when you start your car and it takes, say, 5 minutes to get to 160F coolant temp, for 5 minutes it is going to be closed.

If your car is at 240F after two minutes STARTING FROM COLD then the thermostat is incredibly unlikely to be the culprit.

Most likely candidate? Air pocket in the coolant system.

Kingtal0n

The hold in the back of the pump needs to be "unblocked" by the thermostat to allow water arriving from the engine I think, hot, (it tried to go out the heater core also but mine is plugged...) and so it goes right back into the engine if that hole is shut. Either that or something like it I am still tryna figure this out.

Something about the shape being different is causing it to stay plugged or maybe it just leaks. I will confirm with measurements when I get the new pump if possible... otherwise... chalk it up to me being dumb... could be the shape of the hole is staying open or closed.

Watch this video


the hole originally is blocked because when I put the thermostat into the pump, I can see it blocks the hole, the spring kinda compresses a little as the plunger on the end bottom out into the hole. There is no travel towards the hole from there either, it appears that the thermostat opens it later when warm. You can look at the thermostat to tell this is what happens, I think, there is no travel towards the hole only away. So really I am still kind of confused what is going on here if you have any suggestions about flow direction. The thermostat definitely seems to plug that hole when its cold so I dont know what that guy is talkin about.

Kingtal0n

Also just to re-re assure you, I removed the thermostat while the engine was overheating 200*F+ and confirmed it was indeed open when removed. I watched it shut before my eyes in the air.

Also my engine is using 4-corner steam ports. so I manually sucked the water into that hose from the heads to ensure no air was in those lines.

I am super, super careful

It went to 240* after I drove it couple miles actually before I caught it. I got stuck in traffic and didn't mean to go far from the house but the traffic is so bad here it was immediately engulfed. I don't have a coolant gauge and rely on the computer behavior atm to tell me if its overheating (it never has), so I noted right away when the limiter kicked in at 2500rpm and the a/f got really rich it was too hot and just got home in time to connect HPtuner and see 240*F.

When it cooled to 190*F I tried again and saw it climbing fast.
I tried another couple things and it went 160 -> 200* couple minutes after that still something wrong. The water is circulating as if the engine was in "heat up mode" so it has to be something with the thermostat since thats all I changed. They are different shapes so it fits. I am going for simplest explanation here... Main reason for the thread is how come nobody is aware there are 2 different kinds of thermostats? It doesn't say anything on the internet anywhere about this. Are they new to the market or something?


Gave up for the night, 8 hours no food just got done changing control arms, ball joints, all kinds of stuff I was beat so called it, waiting on new pump

Kingtal0n

Alright I think this is the answer. the guy in the video is right and everything makes sense once I saw this

The cold coolant, I guess, Apparently, and I did not know this, open the bypass valve to put the engine into "heat up" mode. This is why you cannot remove the thermostat from an LS style water pump (apparently) because now the coolant can go through that hole and the engine will overheat. this also explains why looping the heater core is a terrible idea, as it creates a short circuit the same as having the hole open under the bypass.

So I guess my bypass is staying open due to the shape of the different thermostat. /simple enough

lionelhutz

The shape doesn't necessarily mean one can't work but the other can. They could interchange just fine. The one with the taper would just have to be a little longer so it still blocks the hole when it opens.

Kingtal0n

The issue is that apparently the hole is NOT being blocked. Once the hole is blocked the water is forced into the radiator. So it must be that the flat design is unable to properly block the hole for the tapered design. I felt it bottom out when I installed it, so it was def pushing into the hole like you would expect. It must not fit though. Incredible how such a small hole for water causes such a huge problem.

Kingtal0n

Gates pump in, flat style thermostat, working perfect.

Much to my relief the issue is resolved, but still leaves only questions.

I couldn't find the HarborF micrometer in time but I did stick a drillbit down into both old and new pumps. They seem to be exact same length. Furthremore I compared the holes and they also appeared the same.

I honestly have no idea why the one thermostat doesn't work and the other does. I wasn't about to test the other style once I had it fixed though, sorry. Im just glad thats overwith.

lionelhutz

Good you fixed it, but I expect you have something else going on besides just the thermostat not quite blocking that hole.

If the "bad" thermostat had embossed bumps on the bottom of that disk then it would not quite seal against a flat surface. But, it would restrict the hole enough that most of the coolant should be forced to the radiator. This could lower the efficiency of the cooling system a little bit since it doesn't quite take full advantage of the radiator, but it should still cool the engine.

The thermostat IS NOT a switch that is only open or closed. When it is cool enough and/or you have enough radiator airflow, the thermostat only opens enough to allow the necessary coolant flow to the radiator to maintain a constant temperature. So, not blocking the bypass hole completely does not mean coolant won't flow to the radiator.

So, maybe you have a marginal radiator and fans or maybe you have excessive restriction for the coolant flow to the radiator.

Kingtal0n

Impossible because it never goes above 180*F sitting at idle even with fans off,

It was fine with original water pump for 7000 miles,

I put next thermostat in (wrong kind) and it went to 240*F ,
I put old thermostat back in, and it was back to normal.

I put new water pump in and new thermostat (same one that overheated in the other water pump) and also back to normal.

So my process of elimination leads me to believe its the thermostat

runner140*

Home Depot makes a dryer vent brush/cleaner that's about 3 feet long...that's what I use.