Junk in the poppet valve... again!

**tlwjkw** · 07-27-2021, 09:48 PM

i will... its two completely different systems... ya can't compare tha two. but thats my opinion and ya ain't gonna change it.

**powerabout** · 07-27-2021, 10:29 PM

Originally Posted by David - WI

Yes, it's a myth... but I didn't want to fight this battle.

the proof for all to see comes from Mother Merc and the 2.5.
When the HP went up they had to create more flow.

**tlwjkw** · 07-27-2021, 10:57 PM

tha reason it was changed is 'cause they "stumbled onta something when they added a "jumper hose" in '89 ta try ta help with air pockets and tha stupid water cooled rec/reg................

**powerabout** · 07-27-2021, 11:08 PM

Originally Posted by tlwjkw

tha reason it was changed is 'cause they "stumbled onta something when they added a "jumper hose" in '89 ta try ta help with air pockets and tha stupid water cooled rec/reg................

you do know HP engines dont have a poppet valve as they needed all the flow they could get in the higher HP engines.
Increased the water tube diameter and went to OMC style higher volume pump design?

**tlwjkw** · 07-27-2021, 11:25 PM

mater a fact i do know tha MERC systems quite well both production and high performance both 2.4's and 2.5's... they ran tha small tubes a lotta years (well inta tha 2.5 years) before hi perf. decided it "needed" a bigger tube..... which is basically all that changed along with price...

**powerabout** · 07-27-2021, 11:59 PM

Originally Posted by tlwjkw

mater a fact i do know tha MERC systems quite well both production and high performance both 2.4's and 2.5's... they ran tha small tubes a lotta years (well inta tha 2.5 years) before hi perf. decided it "needed" a bigger tube..... which is basically all that changed along with price...

so flow did need to go up in an outboard ( poppet valve removed as that can shortcut the flow) as they use marine water and a closed system it needs to?

**tlwjkw** · 07-28-2021, 12:11 AM

ya can't apply anything "closed" to tha merc "open" system (except stats with production motors).... last hot rod i had was a 280/switch box motor ran ona '94 plate with tha XR6 gearcase and pump, small tube and had "0" problems............... jmo.

**powerabout** · 07-28-2021, 12:43 AM

Originally Posted by tlwjkw

ya can't apply anything "closed" to tha merc "open" system (except stats with production motors).... last hot rod i had was a 280/switch box motor ran ona '94 plate with tha XR6 gearcase and pump, small tube and had "0" problems............... jmo.

how about
the water
the aluminium
simple thermo dynamics about heat transfer
Have you any experience with vintage cars..all have poor cooling, how to fix add inline cooling pump in the bottom hose to increase the flow.

**tlwjkw** · 07-28-2021, 12:54 AM

the water
the aluminium
simple thermo dynamics about heat transfer"

reason for tha "hot rod" coolin' parts.... reason for "production" parts.......... reason they don't mix well.

"they" do a lotta out of tha box things with anything mechanical but thats not what tha topic of this thread is....... we've said enough.. ain't gonna argue 'bout tha same ole thing over n over again.. we're talkin' 'bout plain ole overheat problem and we got way off topic here.. these are jus my opinions and they ain't changin'................

**rjdubiel** · 07-28-2021, 07:37 AM

Originally Posted by powerabout

coolant flow speed going too fast is old wives tale.
Exit restrictions are either to build pressure or temp or both.

Wives tale for what motor would be my question? just saying if you put steel bores in a 9K rpm motor and do not build heat you will have issues. You also need to watch piston to wall clearance for steel bore high rpm and forged pistons. There is not one solution for all motors. This is a fishing motor we are talking here and it was not dumping enough water as the poppet was stuck shut so it overheated when he was going across the lake. simple as that.

**David - WI** · 07-28-2021, 08:21 AM

Originally Posted by rjdubiel

Wives tale for what motor would be my question? just saying if you put steel bores in a 9K rpm motor and do not build heat you will have issues. You also need to watch piston to wall clearance for steel bore high rpm and forged pistons. There is not one solution for all motors. This is a fishing motor we are talking here and it was not dumping enough water as the poppet was stuck shut so it overheated when he was going across the lake. simple as that.

It doesn't matter if it's a car motor, a boat motor, or a nuclear reactor.

**DieselDood** · 07-28-2021, 08:33 AM

Originally Posted by powerabout

coolant flow speed going too fast is old wives tale.
Exit restrictions are either to build pressure or temp or both.
on an auto you need pressure to stop the pump cavitating at high speed.
check out the wp nascar engines run at..

I've seen it first hand in the Automotive and Diesel world. Vehicle comes in with no Thermostat and overheats running down the highway. Simply add the thermostat, which slows the coolant flow down and it has no issues. But as you said... to "build pressure or temp or both" So to build temp, they slow the flow down so that the heat transfers from the block to the coolant/water, then on a boat, it leaves the motor, but on a car it also needs to go through the radiator and transfer that heat back out.

Nascar run low flow pumps. The pressure in that system is due to heat and expansion, not due to the pump.
Nascar also runs 280-290 degree coolant temps and 100psi of water pressure to raise the boiling point to about 330 degrees.

But.. that aside.. I'm not trying to argue. I could be wrong, but I have read this in text books, been taught it at high level factory training, and seen it first hand.

With this, the poppet gets stuck closed, not allowing the excess water to bypass, which raises pressure and also increases water speed through the motor, and it overheats. At least that's what makes sense to me.

Again... I can be wrong, and I'm ok with that.

**David - WI** · 07-28-2021, 08:44 AM

The things you're describing are caused by other issues/problems, not from the coolant leaving the motor too fast.

Too much flow causing overheating is a myth, according to Edelbrock’s, Smitty Smith. “There is a whole lot of science behind heat exchangers, but the bottom line is more flow will never cause a decrease in cooling performance,” he said.

https://www.chevyhardcore.com/tech-s...-your-hot-rod/

IMPROVEMENT RULE # 1 -Anything you can do to increase the coolant flow rate, within limits described, will improve heat transfer and cooling performance. Anything you do to restrict or reduce the coolant flow rate will hurt cooling performance.

(From this we see that increasing the coolant flow rate will result in better heat transfer performance. There are some cautions to be observed in increasing coolant flow rate, however. Going too far may result in aeration and foaming of the coolant, possible damage to the radiator by overpressure, cavitation of the pump due to excessive pressure drop through the radiator, and erosion of the radiator tubes. The ideal coolant flow rate is one that will provide optimum coolant flow velocity through the radiator tubes in the range of 6 to 8 feet per second. Flow velocities above 10 feet per second should be avoided.)

http://www.ausrotary.com/viewtopic.php?t=202497

**powerabout** · 07-28-2021, 09:01 AM

I have seen people cook engines (4 strokes but not pushrod v8's)when they took the thermos out as the thermo had the valve built into it which controlled the bypass so the water just bypassed the radiator.
You need to check the rad water temp in and out to understand whats happening for a starter

**DieselDood** · 07-28-2021, 09:10 AM

Ok... so in this case... back to this motor...

I'd like to understand why it overheats when the poppet sticks closed.

What is the purpose of the Poppet? I thought it was to bleed off excessive pressure/flow.