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As you can I see did thermostat test. Thermostat on left is Robertshaw high flow, I purchased through Stewarts. Thermostat on right is a standard Robertshaw purchased at a local parts store. 211 degrees on the digital thermometer. I believe the left one is from Robertshaws 'flowkooler' line, Stewarts modified it with three bypass holes.
As you can I see did thermostat test. Thermostat on left is Robertshaw high flow, I purchased through Stewarts. Thermostat on right is a standard Robertshaw purchased at a local parts store. 211 degrees on the digital thermometer. I believe the left one is from Robertshaws 'flowkooler' line, Stewarts modified it with three bypass holes
I initially used the Stewart with the holes. I had erratic temperatures. I just replaced the thermostat with a Stewart high flow WITHOUT the bypass holes. The thermostat acts as is should now. I don't think you NEED the thermostat with the bypass holes imo.
I initially used the Stewart with the holes. I had erratic temperatures. I just replaced the thermostat with a Stewart high flow WITHOUT the bypass holes. The thermostat acts as is should now. I don't think you NEED the thermostat with the bypass holes imo.
I bought the Stewart modified thermostat only because its what they spec for their stage 2 pumps which I have. Otherwise I would have bought a non-modified high flow as you did.
A stage 2 pump does not have a bypass feature. So your pump is cavitating during warmup without the holes drilled in the ts.
This is basically correct that the Stage II pump does not have the bypass feature. It is also correct the High Flow (three 3/16" holes) thermostat is supposed to be used with the Stage II pump.
I don't agree that my pump is cavitating during warm up.
I better check into this further. I'll be back with some more information soon as I get the car out again.
Last edited by Street Rat; Dec 21, 2018 at 04:03 PM.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
It may not be cavitating at lower engine speeds but the pump isn't circulating coolant around the block either. That's why the holes in the ts are required so the pump is constantly circulating coolant throughout the entire cooling system. It's also why it takes the engine longer to reach its operating temp.
This is basically correct that the Stage II pump does not have the bypass feature. It is also correct the High Flow (three 3/16" holes) thermostat is supposed to be used with the Stage II pump.
I don't agree that my pump is cavitating during warm up.
I better check into this further. I'll be back with some more information soon as I get the car out again.
You have a continuous bypass or flow path if you still have to stock heater core connected in the factory configuration.
I also highly doubt the water pump on any GM small block is capable of cavitation. Dead-heading would occur, but not cavitation. The design is way too loose for the pump to be capable of developing vacuum bubbles in the coolant.
Usually drill 3 bypass holes in most std stats also. Most times I use the Milodon stats, have never had a problem.
Not sure if a high flow water pump is needed. have one but cant tell a difference over a std.
Many yrs ago I bought a CAT high flow water pump for $60 at Pomona swap meet just to get the car running..well its still holding up lol.
Think the right radiator and fan setup are more important.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Automotive water pumps can cavitate. Nothing to do with loosness but just plain old physics. Ship propellors can cavitate and they are as loose as you can get.
During 50 years of driving and owning literally hundreds of cars, the only thermostat I have ever had stick closed was one of these high flow styles. That was this last season in my Vette. I went back to a standard old style thermostat and the engine temps are exactly the same as when the high flow was operating properly. I did drill a hole in the standard thermostat. I too have a high flow aluminum water pump.
Automotive water pumps can cavitate. Nothing to do with loosness but just plain old physics. Ship propellors can cavitate and they are as loose as you can get.
Whatever. Dead-heading or restricting the outlet won't cause cavitation that otherwise didn't exist. If restricting coolant flow made the difference between cavitating or not, the restriction would have to be on the inlet of the pump to drop the NPSH low enough to cavitate.
The typical Chevy pump impeller pressed out of sheet steel is more a paddle then a true pump impeller or propeller.
I fell prey to the suggestions to use the modified thermostat. I purchased a Stewart 195 degree stat. The one that has three 3/16" holes in it. Overpriced for sure.
My experience now is that the modified thermostat isn't getting hot enough to open. The temperature gets to 180 degrees and that's it.
So what's worse? A modified thermostat that doesn't allow the motor to warm up? Or a non-modified thermostat that causes cavitation with the high flow pump. Supposedly.
I want my heater to function. I am changing back to the NON-MODIFIED thermostat.
Seems if the block has the bypass-hole at passenger side pump mount pad, And the pump has No hole, And a "no bypass" is an issue, why can't the pump simply be drilled to match?
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Originally Posted by Street Rat
I fell prey to the suggestions to use the modified thermostat. I purchased a Stewart 195 degree stat. The one that has three 3/16" holes in it. Overpriced for sure.
My experience now is that the modified thermostat isn't getting hot enough to open. The temperature gets to 180 degrees and that's it.
So what's worse? A modified thermostat that doesn't allow the motor to warm up? Or a non-modified thermostat that causes cavitation with the high flow pump. Supposedly.
I want my heater to function. I am changing back to the NON-MODIFIED thermostat.
So maybe you can take something from this?
Your modified ts is open ALL the time i.e. its flowing some coolant without opening up which results in longer warm ups.
180* is considered an optimal engine running temperature. Why are you trying for 195*?
Your modified ts is open ALL the time i.e. its flowing some coolant without opening up which results in longer warm ups.
180* is considered an optimal engine running temperature. Why are you trying for 195*?
You are correct about longer warm ups. How about a limited warmup of 180 degrees and below?
I'm only getting limited heat in the cabin during cold weather driving with the modified stat. The 195 non-modified thermostat allows me to have 180 degree to 195 degree heat available for the heater.
The non-modified thermostat works as it should for my desires.
Thermostat High Flow vs Regular Flow
