New Overheating Clue

[shotgunslade]

Just got some new information about the overheating that occasionally plagues our cars. Seems that the water pump for the 4 cylinder Subaru engines has a tendency to cavitate over 6700 rpm. It might be that our water pump has the same problem. Cavitation occurs because the water pump creates an area of lower than atmospheric pressure that allows the coolant to boil at a lower temperature, creating steam bubbles in the coolant stream. That might be why a higher pressure radiator cap would help this problem, causing the bubbles to collapse sooner, before they have an opportunity to create havoc.

I have had a lot of difficult finding an "import" size high-pressure radiator cap. I have ordered a Crucial 1.4 bar cap (approx 20 psi), from Crucial Racing Products. Will be at Pocono next Friday and will post how it works.

[sicksubie]

Any aftermarket STi cap will fit our cars. I have a 18.6psi ( I think) Sti radiator cap on my OEM radiator right now

[SVXRide]

Originally Posted by shotgunslade

Just got some new information about the overheating that occasionally plagues our cars. Seems that the water pump for the 4 cylinder Subaru engines has a tendency to cavitate over 6700 rpm. It might be that our water pump has the same problem. Cavitation occurs because the water pump creates an area of lower than atmospheric pressure that allows the coolant to boil at a lower temperature, creating steam bubbles in the coolant stream. That might be why a higher pressure radiator cap would help this problem, causing the bubbles to collapse sooner, before they have an opportunity to create havoc.

I have had a lot of difficult finding an "import" size high-pressure radiator cap. I have ordered a Crucial 1.4 bar cap (approx 20 psi), from Crucial Racing Products. Will be at Pocono next Friday and will post how it works.

Dan,
Good point. Now we just have to find a better water pump
-Bill

[GreenMarine]

Originally Posted by SVXRide

Dan,
Good point. Now we just have to find a better water pump
-Bill

Lets design some better impeller blades Bill and then submit the design to Subaru and see if they pick up the design

~ Chris

[Nomake Wan]

Damn... and I just ordered a new water pump to go with my 60k mile service parts, too...

[SVXRide]

Dan,
Do the wiz kids at your firm have the tools to model the EG33's water pump? (yeah, I know we're flowing water, not air)
-Bill

[svxpert]

<<New Overheating Clue>>

what kind of over heating problems do the SVX have? I have never heard of this with the SVX I had. most of the overheating problems that Subaru owners have are self inflicted (they don't know how to properly bleed the air out of the system. )

[SVXRide]

This is "track-induced" overheating, not every day, run-of-the-mill overheating
-Bill

[Nomake Wan]

Originally Posted by SVXRide

This is "track-induced" overheating, not every day, run-of-the-mill overheating
-Bill

What he said. Running at high loads above 3,000 RPMs for longer-than-normal periods.

[CorSVXette]

Originally Posted by svxpert

(they don't know how to properly bleed the air out of the system. )

How do you do that

[SVXRide]

RallyBob has a good post on how they do this for the EG33RS race car. Think it's in the 285 WHP thread.
-Bill

[shotgunslade]

Those of us with MT's, at the track, will continuously take the engine over 7000 rpm. I've hit 7200 at the end of straights when I didn't want to upshift before the corner.

I'm wondering if an underdrive pulley might also help. Any comments from underdrive pulley users. Any downsides? Dead batteries, overheating while idling, etc?

Bill:

Yes we have the software, and even have the expertise to do liquids. What we don't have is the expertise to do a 2 state problem. Pumping cavitation is a very very complex problem.

Just because we have a set of chisels doesn't make us Michelangelo.

Dan

Dan

[SVXRide]

Originally Posted by shotgunslade

Those of us with MT's, at the track, will continuously take the engine over 7000 rpm. I've hit 7200 at the end of straights when I didn't want to upshift before the corner.

I'm wondering if an underdrive pulley might also help. Any comments from underdrive pulley users. Any downsides? Dead batteries, overheating while idling, etc?

Bill:

Yes we have the software, and even have the expertise to do liquids. What we don't have is the expertise to do a 2 state problem. Pumping cavitation is a very very complex problem.

Just because we have a set of chisels doesn't make us Michelangelo.

Dan

Dan

Dan,
Agreed. But I thought you were hiring "budding Michelangelos" out of college? This would be a case to ask Subaru Engineering how they model cavitation. Shame we don't know anyone "on the inside"
-Bill

[RallyBob]

Originally Posted by shotgunslade

Those of us with MT's, at the track, will continuously take the engine over 7000 rpm. I've hit 7200 at the end of straights when I didn't want to upshift before the corner.

I'm wondering if an underdrive pulley might also help. Any comments from underdrive pulley users. Any downsides? Dead batteries, overheating while idling, etc?

Just about every race engine I've ever built I've had to slow the water pump pulley down on. Most factory water pumps are driven a little bit faster than the crank speed. Running an engine at 1000, 2000, or even 3000 rpms higher than the factory anticipated usually results in cavitation and overheating.

For a street engine I typically slow the water pump down by the same amount it is overdriven. In other words, if the pump spins faster than the crank by 10% (example: 6600 rpm pump speed @ 6000 rpm crank speed) I will reduce that speed to 90% of the crank speed (5400 rpm pump speed @ 6000 rpm crank speed). Nothing scientific about it, just trial and error on my part. For racing I will knock the overall pump speed down by 35-40%, but this can create overheating at slower speeds so it's not recommended for road use.

[SVXRide]

Hey, Bob, not to get too off topic in this thread, but do you happen to have the part number on that PS pump?
-Bill