'92 C115 Yamaha water pressure problems

[enmcneely]

’92 - C115 Yamaha. One year ago temp alarm sounded and water press gauge showed 5 psig. Mechanic said the impeller had "spun" on the shaft. First use after new water pump, I noticed initially good water pressure then a severe drop in pressure upon first throttle up. Mechanic determined the water pressure regulator (poppet) had stuck in the open position. He blamed higher water pressure from the new water pump and corrosion. After new poppet valve and spring, and two new thermostats for good measure, no more temp alarms and water pressure at 17 - 18 psig at cruising speed. Last week the pressure was running 12 psig at 3800 rpms and would drop even lower when the engine speed increased. Running very long under 10 psig caused the high temp alarm to sound. When I would stop and let the engine idle down for a few seconds, I could put in gear and throttle up and the pressure would go up to 18 - 20 psig, but would began dropping again after a few seconds. If I did not put it in gear and increased rpms, the pressure would hold near 20 psig, but as soon as I put in gear and throttled up, the pressure would start dropping. No obstructions can be seen at water intakes and the pee stream has a seemingly good flow.

 

[nahanni]

Re: '92 C115 Yamaha water pressure problems

Hello,<br />I am having the "exact" same problem with my 98 c115. I sure hope someone will come up with a solution or probable cause for this. Very Frustrating......

 

[Ray Neudecker]

Re: '92 C115 Yamaha water pressure problems

First, I would check the compression to be sure I didn't have a leaking head gasket. I would also disassemble and clean the poppet valve and seal.

 

[huanca]

Re: '92 C115 Yamaha water pressure problems

Having EXACTLY the same problem: Did you solve yours? How? Please?<br /><br />Yamaha 140 BET 4 cyls 140 HP outboard, premix, 6 x 3 months seasons is salt water (aprox 300 hours). Off seasons ran it weekly for 15 minutes with the garden hose and muffs.<br /><br />Last year it started overheating past 4000 RPMs, sometimes: pressure would climb up to 20 psi and suddenly start to drop to 2 or 4 psi. Took it to idle and restarted and sometimes it would stay OK at around 16 psi, others it would go down again to 2 or 4 psi. Apart from that, never a problem. <br /><br />Spark plugs and lower unit oil changed twice a year. Always started (except for a bad battery once which cured it for good). Impeller changed once every 2 years, and greasing points relubed yearly.<br /><br />Last week I changed the impeller, head gaskets, cylinder zincs, Tstats, and removed some sand and salt from head cover, Tstat housings and everywhere I could reach with a wire or hose. Flushed it several times and to the ocean. Ran this weekend OK upto 4,000 RPMs. At idle in less taht 10 seconds pressure clibs to 6 or 8 psi. At 4000 RPM pressure upto 16 psi, after 10 seconds or maybe 20, pressure slides down to 2 or 4 psi and temperature starts to rise. I think it used to go higher to approximately 20 psi before. Tell tale shows a good??? stream of water. Tried replicating this in neutral with no success although the water pressure will rise above 20 psi at over 4500 RPMS in neutral. Been able to replicate the probelm reliably this weekend while in gear. My idea is that the poppet valve spring is weak (salt water, 6 years) and running at speed creates a vaccum which aids the poppet valve opening. Since this vacuum is not present at dile, I cannot replicate this in neutral.<br /><br />I will try to open the poppet valve with water pressure and a gage to see what readings I get.<br /><br />Can anyone confirms these ideas for me?<br /><br />Can anyone confirm how the poppet valve should be placed: long end towards the engine or short end towards the engine?

 

[enmcneely]

Re: '92 C115 Yamaha water pressure problems

Yes, I think my overheating problem has been solved. I enlisted the help of a local OB mechanic who found two problems. The metal tubing from the discharge of the water pump enters the bottom of the engine and is sealed at the entry point by a rubber sleeve. This rubber sleeve had partially popped out allowing some water pressure to be lost. He also found considerable corrosion in the cooling passages which was causing loss of heat transfer. A reduced cooling water flow plus the corrosion was causing the overheat problem. He removed the corrosion and replaced the rubber sleeve and I have had no problems, having put approx. 30 hrs. runtime on it since. According to the mechanic, normal pressure is 10 – 12 psig at wide open throttle which is what I am seeing now. At lower rpm’s, the pressure is higher. <br />As for your situation, it sounds like you have a poppet valve sticking open resulting in the 2 -4 psig pressure you’re seeing. Remove the cover, then remove the poppet valve and spring. I suspect you will see some corrosion which you should clean thoroughly. If you have not replaced the poppet valve before, I suggest you do so at this time. If this doesn’t correct your problem, you may have a problem similar to mine. Also, I’m not sure if it really can cause a problem, but I’ve always been reluctant to rev up my engine in neutral past about 2,000 rpm’s.