Water Pump speed

[nawlins-tim]

My motor temps jump up a little too much once I get to highway speed for 10plus miles at say 2500rpm. All of my motors in the past cooled down on the highway and had problems in traffic. And it was worse, getting to 200*, but a new radiator brought it down a bit but still the temps go up once I hit the highway.
I'm wondering if my water pump is Over driven too much? I have a 6.25in water pump pulley and around an 8in crank pulley. I did all the other checks like having a spring in the lower hose. The timing could be better with a vacuum advance can but without it I'm all in by 2500 or so. And I shouldn't be too lean with 72 jets in front. However It wouldn't hurt to check my fuel pressure at highway speed, but the motor runs fine with No hesitation.
Anyway does anyone think I would be better off with a smaller crank pulley. Cuz I may be getting that cavitation thing at steady upper rpm. What do ya think? What's your pulley sizes like. ? One to one? under or over-driven pulleys?

 

[bill]

My motor temps jump up a little too much once I get to highway speed for 10plus miles at say 2500rpm. All of my motors in the past cooled down on the highway and had problems in traffic. And it was worse, getting to 200*, but a new radiator brought it down a bit but still the temps go up once I hit the highway.
I'm wondering if my water pump is Over driven too much? I have a 6.25in water pump pulley and around an 8in crank pulley. I did all the other checks like having a spring in the lower hose. The timing could be better with a vacuum advance can but without it I'm all in by 2500 or so. And I shouldn't be too lean with 72 jets in front. However It wouldn't hurt to check my fuel pressure at highway speed, but the motor runs fine with No hesitation.
Anyway does anyone think I would be better off with a smaller crank pulley. Cuz I may be getting that cavitation thing at steady upper rpm. What do ya think? What's your pulley sizes like. ? One to one? under or over-driven pulleys?

So your saying the temp falls in traffic and goes back up when you hit the highway? That is rather unusual. I would have to say that your radiator may not be large enough, your t-stat may not be the right temp, etc.

 

[Pontiac455]

I would bet the clutch fan is slipping at higher rpm.

 

[pontiacgp]

what do your plugs look like, sounds like your too lean and causing the engine to heat up. We had an overheating issue on the race car and went up a couple jet sizes and it cooled it down. BTW 200º isn't overheating or running too hot

 

[DRIVEN]

I would bet the clutch fan is slipping at higher rpm.

+1 to that. I've seen it before.

 

[pontiacgp]

I would bet the clutch fan is slipping at higher rpm.

+1 to that. I've seen it before.

my fan never comes on when on the highway, the air passing through the rad is more than the fan can pull

 

[bill]

I would bet the clutch fan is slipping at higher rpm.

+1 to that. I've seen it before.

my fan never comes on when on the highway, the air passing through the rad is more than the fan can pull

X2

 

[tc1959]

I had a Z 28 that would do that, After I put 3:73 gears in it. The water pump was turning too fast causing cavitation in the coolant. The car would just get hotter and hotter on the freeway. I solved the problem with a Moroso electric water pump.
I think you are on to something slowing down the pump. I would fix the vacuum advance also.

 

[nawlins-tim]

I would bet the clutch fan is slipping at higher rpm.

+1 to that. I've seen it before.

my fan never comes on when on the highway, the air passing through the rad is more than the fan can pull

The clutch fan is new and It Is supposed to slip at higher rpm but then again it is a thermal clutch so at TEMP it is supposed to engage. Who knows?
Ive got to check the plugs after a highway run. I just didn't think a 750 cfm carb with 72 front jets would be enough at cruise, which is where my problems are. I think I'm gonna order a smaller pulley tonite.