F80 Pressure Control Valve?

[AGENT 37]

I'm ordering thermostats and a few other parts for my 1999 F80 and was reminded of a question I've had for a while......

What does the "pressure control valve" that is in the exhaust cover actually do? (Item 19, 20, and 21)

http://www.boats.net/parts/search/Yamaha/Outboard/1999/F80TLRX/CYLINDER CRANKCASE 1/parts.html

Both engines were showing "froth" in the dipsticks and the top of the valve cover. One corrected itself, but the other motor has discolored oil (think dark milk-chocolate syrup) and still has the "frothing" evidence that it has been running cool. I've been running in 20F air / 38F water and it is not the typical severe sign of water in the oil. I've just changed the oil and filters and don't plan to run them until the new thermostats are installed.

I was going to do the functional test but wound up bending the thermostats upon removal so I will just replace them.

Any other suggestions? And what's the function of the "pressure control valve"?

 

[AGENT 37]

Re: F80 Pressure Control Valve?

Mueller.....

 

[99yam40]

Re: F80 Pressure Control Valve?

Re-leaves water excess pressure during high RPMs of the motor.
Seals back off at lower pressure and RPM to keep the motor full of water. If it sticks open it can cause hot spots on upper parts due to not having the motor completely full

 

[AGENT 37]

Re: F80 Pressure Control Valve?

How about if stays stuck closed? Would engine run cooler?

I have minimal moisture in my crankcase and the telltale is weak.... decent pressure while running and pumping through the gearcase, but just a dribble when I hook the hose directly to the flushing adapter with the engine off.

I know that a cool running engine due to a closed pressure control valve and a weak telltale due to an open control valve are two conflicting conditions......

Any ideas?

 

[99yam40]

Re: F80 Pressure Control Valve?

Why not pull it and inspect to see. It is a regular maintenance item just like the stats and water pump

 

[AGENT 37]

Re: F80 Pressure Control Valve?

I received my parts today and swapped them out. What a stupidly simple concept.

The PCV and grommet were clean and intact. I'll have to see how the outboard does with the new thermostat and PCV.