Hi everyone, I know this has probably already been discussed here several times, but I'm really confused. Today I replaced the water pump on my 2001 Corvette C5. The original pump had a thermostat with a 2-bolt flange. The new pump also takes a thermostat with 2 bolts. I installed the new water pump, and then I noticed that the new thermostat I bought has a 3-bolt flange. So I used the original thermostat with the 2-bolt flange, but I noticed that the new 3-bolt thermostat won’t fit into the original pump (it has a narrower opening), but it does fit into the new pump, because the opening is wider. (I still used the original one, because it matched the 2 bolts.) So what should I install to make it correct? I guess I need a wider thermostat (to fit into the new water pump), but with a 2-bolt flange. Ideally, I’d like the thermostat to be 160 degrees. Can someone please help me figure out how to build this hybrid setup — and where I can buy the right thermostat? Thank you!

 

[QUOTE=Pavolc5;1609009993]Hi everyone, I know this has probably already been discussed here several times, but I'm really confused. Today I replaced the water pump on my 2001 Corvette C5. The original pump had a thermostat with a 2-bolt flange. The new pump also takes a thermostat with 2 bolts. I installed the new water pump, and then I noticed that the new thermostat I bought has a 3-bolt flange. So I used the original thermostat with the 2-bolt flange, but I noticed that the new 3-bolt thermostat won’t fit into the original pump (it has a narrower opening), but it does fit into the new pump, because the opening is wider. (I still used the original one, because it matched the 2 bolts.) So what should I install to make it correct? I guess I need a wider thermostat (to fit into the new water pump), but with a 2-bolt flange.
IF you have an original LS1 water pump, the original thermostat and thermostat housing is a one piece assembly. The one piece assembly WILL NOT fit into the later water pump design that was released about 20 years ago (later 2004/LS2). The later water pump design accepts a two piece thermostat and thermostat housing. The number of holes in the flange is meaningless to the operation and function.







Stay with a stock thermostat temp. There is no benefit to a 160 thermostat from a performance perspective. Once the engine reaches operating temp, there is no difference.

 

It’s all a bit tangled up .
Of course, I’m not the first owner, so I don’t know what was changed before.

So, to sum it up:

1. On the “old” water pump I removed (2 bolts for the thermostat), the 97–03 thermostat (3-bolt) didn’t fit — it wouldn’t go in (I accidentally ordered a new thermostat with housing, the older 97–03 type).
There was actually a 04–08 (2-bolt) thermostat installed in it.



From that, it follows that the water pump and thermostat were probably already replaced in the past with the newer type, right? That’s why the old-style thermostat didn’t fit.

I installed the new pump, and at that time I didn’t yet know all this. I wanted to use the “new” thermostat I bought (97–03, 3-bolt), and that’s when I found out that the pump had only 2 bolt holes while the thermostat housing had 3.
So I used the thermostat and housing from the old pump (which was probably already the newer type).

Do I understand this correctly?

The only thing I’m still confused about is that the old-style thermostat could be inserted into the new pump.
The pump had 2 holes, and the thermostat housing had 3, but the opening diameter was fine, and it could be inserted.

I don’t know what to do now — is this OK or not?

 

Pictures would help.

 

Yes, I am sending photos. 1. The original water pump that was on the car. 2. The thermostat that did not fit into the original pump but did fit into the new one. 3. The new water pump that is currently installed on the car. I installed the original thermostat with the flange on this pump using two screws.Before fastening, it was necessary to slightly press the thermostat with the flange against the spring, as the thermostat was already touching. It only needed to be pressed about 3 millimeters.

 

Ok. I hope this works out for you.

 

I have already done it.I just don’t know if it’s correct, as I described my problem and I’m trying to find out from you I’m also wondering if it’s normal that the thermostat needed to be pressed slightly before screwing it in.

 

I cannot speak to your specific issue. I am also not familiar with the brand of water pump you installed. I have replaced at least 10 LS water pumps in the last 15 years, and have not seen a new water pump that would accept the old one-piece style housing I have also only used GM water pumps and thermostat housings.

 

I’m going to lose it. The manufacturer just replied to me saying that the pump they sold me isn’t the right one. Even though, according to my search, it showed up as the correct one. Of course, I’ll replace it with the right one. But it seems that this one works too. It’s exactly the same, the motor is cooling properly. The only difference is that the opening is also compatible with the old type of thermostat. Do you think I could have messed something up?

 

I doubt any harm as been done.

 

I agree with Lucky on the 160° T-stat. I wiil say that the only time a 160° stat is beneficial is if you've had the fans adjusted to activate sooner, and, perhaps, installed a larger radiator. I have installed a 160° stat, but also have a larger DeWitts radiator, and the fans activate at 194° coolant temps. In 85° temps my car runs at about 180° at 70mph freeway speeds. Around town at long lights in the same 85° weather, it sometimes hits 200°. A 160° stat DOES NOT mean 160° coolant temps! The car going 70mph will run at whatever temps it will run at. In other words, it is what it is. A 160° stat only delays warm up. However, it will allow the engine to run somewhat cooler than a 195° stat. Hope this all makes sense.....

 

The thermostat temperature is now not too high. I’m still thinking about that pump. It also occurred to me that the pump I put in is the older model — the first type that was made. That’s why it could fit both the 3-screw (one-piece) thermostat and the 2-screw thermostat. I installed the 2-screw thermostat (the new type that can be disassembled). But that would make sense — it’s simply a new part, but it’s not the new type of pump, it’s the original type of pump.

What do you think? Because if that’s correct, I’ll just keep this pump and install the 3-screw (one-piece) thermostat instead. I’m just not sure whether the new type of thermostat can also be used there or not.

The brand is fine. These are our brands here in Europe. I’m also seeing your brands for the first time.

 

First off, the boss that looks like a third bolt hole isn’t a bolt hole. Ignore it. Cut it off if that makes you feel better.

The pump you show looks to me like it will accept either the early one piece thermo/housing unit or the later two piece that became std on the trucks.
the thermo fits into the housing, and acts as the gasket as well. No stupid O-ring.

And yes, the stat hits the bottom of the hole before the housing hits the pump. Just hold it down while installing the bolts.

160 thermo is fine. But don’t expect 160 coolant temps unless it in the 30’s outside and you are on the freeway.
Fans control the temps at slow speeds. And they don’t move enough air to keep these things below 180.

 

Thank you for your response.How can I find out which thermostat I should use? Since my pump can fit both the older and the newer type The older type of thermostat did not make contact with the pump the way we describe it with the new type of thermostat.

 

I’d use the later style.

 

Thank you for your help.
What is actually the correct part number of the water pump?

 

If you want GM.
Water pump - GM 251744
Thermostat housing/thermostat assembly - GM 1511057

 

Yeah, nobody knows why GM put 3 holes in the housing....

 

 

It hasn't happened, yet....But I'm waiting for the guys to post up that think your engine overheats with no Tstat because the water rushes thru the engine so fast it has no time to pick up any heat!!!