Ok so I have some thoughts I would like the engine builders to think about and respond to.
We have discussed many times the coolant overflow or puking out of the top of the overflow bottle on a twinned built motor Z.
The general consensus from what I gather is that its a blown headgasket, and that there is no way for the engine to "pressurize" the coolant system without it going through the headgasket.

My thought: I "think" thats its possible that the waterpump on a boosted Z "cavitates" when you boost the engine.

Air in the system is supposedly what causes the thermostat to not open, overheat and puke coolant out of the top of the bottle is it not?

So the same way the "TOTALLY SUBMERSED" prop on a boat cavitates when it goes from zero to 3000 rpm and you see bubbles in the wake, couldn't the "gear rotor" water pump do the same?

Ok so I removed my thermostat months ago. My Z is a weekend car( built motor greddy twinned) and cruising around I see temps from 180-205 depending on traffic, load etc in 95-100 degree heat.I also have the KOYO 53mm radiator.Greddy radiator cap as well..

About every three weeks or so I will notice my coolant overflow bottle is nearing the top. I will elevate the nose on ramps, install a "radiator funnel" and warm the car with the heater on and pour the contents of the bottle back into the radiator and what will remain is about the 1 inch of coolant I started out with when I removed the thermostat and refilled and purged the car months ago.

I am NOT losing coolant..there is no "milky oil" on the dipstick and no oil in the coolant. My car does not run hot but yet mysteriously my overflow bottle will fill up and need to be poured back into the radiator about every three weeks.( I would have to say it happens about every 250-300 miles).

SO I am no expert engine builder but these are my thoughts on this subject and would like to read some opinions on this.
Tom

 

water pump speed is rpm dependent not hp dependent,your theory doesn't hold water(get the joke?).you do know a bad radiator cap will give you the same symptoms right?

 

rising and falling overflow bottle is normal operation....

your coolant will be fizzy with a blown headgasket. have particles of carbon in it.

 

Yes.... water pump speeed is rpm dependant, but in higher horespower applications your going engine is accelerating much faster, and that rate of acceleration could cause the pump to cavitate. Not saying it does, but it is a possibility.

Electric pump anyone?

 

Removing the thermostat is a bad idea. It doesn't just regulate the temp. It regulates the flow as well. How is the coolant suppose to cool down when its flowing through the engine so fast.

 

ok another thought I meant to mention and jetpilot hit it on the head...I dont know about your car but mine will spin from say 2000rpm up to 7000 in nothing flat. Thats why I think it would be really easy for it to cavitate..

go-fast ..my radiator cap is a brand new greddy cap...

my coolant has never been "fizzy" I can see what you mean though..makes sense..

weak-350Z ..the KOYO53mm is enough to cool the coolant..it does for me anyhow in 100 degree heat
I cant imagine how it would harm anything with the coolant flowing continuously through the engine..


Once again..just my thoughts on the matter..

 

rising and falling is normal,but it should never take air into the sytem(that is the whole point of a overflow bottle)

 

+1,some type of restictor should be used even if it's your old stat gutted.

 

go-fast ..my radiator cap is a brand new greddy cap...

nowadays especially,new does not always equal good,for the cost of a cap i would eliminate the possibility by replacing it anyway

 

You are saying that your overflow bottle is full when the engine is cold? Stock size overflow container?

 

Mine does it every other week or so, and it will over flow if the nose is on any sort of downward angle.. But usually it will just fill up, bubble a bit, and the radiator will suck it all back in from the overflow within a few minutes. I'm not over heating, i've just sort of learned to accept it.
The accceleration theory; What if your just sitting there revving your motor, with a light flywheel, you can rev your car faster than it accelerates. asside from first gear that is.. a lot more people would have this problem, even all motor guys.
But in my case,itsusually after a flatout run down the highway that will do it.

 

No what he's saying and is true is that the coolant cannot draw heat from parts of your motor if it is racing by at high speeds. You need to slow the flow down with a restrictor if you're going to remove your thermostat so that the coolant can absorb heat from various parts of your motor. The water passages on your motor were designed using fairly sophisticated computer modeling to achieve a very specific flow around certain parts of the motor to keep things from getting too hot in some places and too cold in others. Part of that is the flow through the thermostat. Even full blown race cars that use no thermostat will run a restrictor in it's place.

I personally wouldn't recommend removing the thermostat on any car that's street driven, you need to be able to control the rate of cooling when you're not getting a constant flow of air through the radiator.

 

I've been really banging my head about this issue. Cavitating dose not put air in the cooling system, it's just water forming a steam pocket when it reaches a pressure where it can flash off and then return to liquid, as the cooling water heats up it's easier to flash but then again as it builds pressure it makes it harder to do so.

I still think it's boost air getting into the cooling system somehow, be it thru the head gasket or somewhere else. I'm pretty sure that my headgasket is trashed and I have my car going into the shop in a few days. Looking at a schematic of the cooling system it shows that the plennum has water plummed to it, I'm guessing to prevent ice forming in in the throttle body in cold weather.

As for the cooling water moving thru the engine too fast, I can't see that being a factor for removing heat, however as the velocity of coolant increases this creates a decrease in pressure of the coolant. That said if the flow were moving too fast in an area such as passing from the block thru the head gasket via a small port it could cause flashing and that would surely create a localized hot spot, most likely when we could least afford it like 5k rpm @ wot. So maybe having a restrictor or thermostat is a good idea in theory.

 

Great responses all....UPREV I met you guys with Josh out at the Texas Heat Wave...stopped by your tent..I appreciate the T-shirt!
I guess I'll order another Nismo thermostat and try it again...

Still would like to hear Sharif's response and a few others...

 

so no opinions from the engine builders?..I really wanted to hear from them..

 

you got advice from engine builder's....you just chose to disregard it.

 

go-fast.....yeah thats funny..where's Sharif's response or any other sponsor here? are you an engine builder? doesn't look like it..

 

as a matter of fact......nevermind,gl w/your problem

 

Red Rider....go-fast is more than qualified to help you. He's up there with the top guys..

Like he said about the rad cap...I changed mine to a new Z32 cap and things are better now. I think my worn out Nismo cap wasn't holding pressure very good.

 

go-fast, I think he was looking for some input from the same people that are more than willing to take our money. You know the professionals, the guys that sell you the greatest next thing that comes out. Or they will do like always keep there mouths shut for the hard questions. Hush hush don't talk about it or we will loose major $$$$$ if we discuss the problem and can't sell anything.