Low water pressure at idle...2003 Yamaha 150 hp vmax.

[Bassin46]

(2003 yamaha 150hp efi vmax vx150)Problem...Only 0-2 psi on (New) water pressure gauge at idle,visual water stream is present on rear of motor,17-20psi at 4000-5500rpm.No overheating Yet!Rebuilt water pump to include plate,gasket,o/rings,impeller....Twice! Same problem....idle is 600/700 rpm.Motor well maintained flushed regularly.Thought I had 5-6psi water press. when brand new at idle???? Thanks for any help!

 

[Captain Paul]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

could be pressure relief valve. I was told by a respected poster on this site it could be a cause of an overheat on my vmax when I was running on the muffs. I am also installing new thermostats, but I don't think thats a low pressure possibilty. On my ox66 the prv appears to be behind the computer on the low end, has a big black hose on the bottom of it. I'm going to try and take it apart tomorrow. Does not look like a horrible job.

 

[Bassin46]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

Thank -you! Did try cleaning prv...not much found to clean....put back together...still same low pressure problem.Next going to remove starboard side tstat....increase rpms above idle...if a good stream of water shots from removed tstat AND water shooting from top of moter block (water press. gauge connector)....was told not to worry about 0-2 psi at idle?Got this info. from a marine tech. at local boat dealer?

 

[Captain Paul]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

Mine has never been really strong at idle either and I do not have a water pressure gauge. Where does the line connect to the block? Is it just a small pickup tube running to the gauge?

 

[Bassin46]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

The water press.fitting on my 2003 Yam vmax is on the port side (left)...top section of powerhead just above tstat.(small barbed brass fitting)Tried the above mentioned test removing starboard side tstat.Lots of water flows out tsat hole in powerhead when increasing rpms slightly above idle.Also shot a 18in stream of water straight up from port side water pressure fitting!Decided to replace BOTH tstats while at this point....Water press. at idle is now 3-4 psi...slight improvement...happy something panned out!Other pressures at higher rpms look great....1000 rpm 5psi,2500rpm12-14psi,3500-4000rpm 16-18psi,any higher rpms 18-22psi on water press. gauge.Going to keep eye on pressures....but get back to fishing!Good luck with your Yam.and THANKS! for your help and input.If I can help you anymore let me know!

 

[Captain Paul]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

That is some pressure. I may invest in a gauge. One more thing to play with. Thanks Bassin. I just did my stats and pressure control valve this morning. The pcv was a bit grungy, I cleaned and re-installed. Thank you Rodbolt for the help. After I tightened it all up,I wondered about adding a very light coat of silicone spray to the pcv and rubbing some on the inner gasket. Has anyone tried this, or just stick with a regular cleaning schedule.

 

[richardr]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

happy sat.
I have a problem with over heating alarm going off at high rpms it runns fine when the engine is running at 3800 and under .its a 1996 saltwater 200.
also my pressure garge is not working at all I wounder what is the problem with that?? I was told maybe the water jackets have to be cleaned out again.
The problem is that I dont use the boat enough .any words of advise for water pressure garge?Also the pissing never gets hot maybe warm but not hot so am i really over heating ??
rich r

 

[TonyNoriega]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

On my 200hpdi which idles at 600-700 rpm, I never get more than 3-4 lbs of pressure at idle. At operating rpm's it goes up to between 15 and 20. I've never really known exactly what I should expect but all seems well with what I'm getting.

 

[rodbolt]

Re: Low water pressure at idle...2003 Yamaha 150 hp vmax.

when you clean the pressure relief valve you really need to remove and discard to old grommet,use a pick and carefully clean the pocket of corrosion and replace the grommet with a new one.
as the tell tale streamis picked off at the point of water entry into the motor it should always be cold even if the engine is boiling.
all it is is an indicator that the pump works, well on certain engines with a water cooled voltage regulator it also cools the rectifier/regulator assy.
but the poppit valve and the t-stats and seals all aid in controlling water presure and must be maintained.