91 Merc 150 - Re-assembly questions

[91_Arriva_150]

Howdy all,

Yeah, newb here. Troubleshooting an overheating problem on my 91 150 Blackmax hanging on a 91 Arriva (no jack plate).

Cliff notes:
- No temperature or pressure gauges, just the auditory continous beep after 15 seconds of being on plane.
- New t-stats, new poppet valve. Water pump replaced 6x in my 18yrs of ownership. Current one has 1.5 seasons.
- Tell-tales show reasonable water pressure, increases with RPM.
- Only run out at the lower colorado river (i.e fresh water).
- Backflushing thermostat openings and poppet revealed no sand in the system.
- Problem developed over the last 2 trips after many years of trouble-free use with typical preventative maintenance.

Talking with old timers, they pointed me to pressurizing the cooling system.

I have the heads off and will be resurfaced to 0.003 flatness max lenghtwise, 0.002 max widthtwise unless directed otherwise. Will be replacing the exhaust manifold gaskets at this time as well.

My questions are:
1. When re-installing the head gaskets would a thin coat of copper-spray-a-gasket be of any benefit?
2. The cylinder head bolts utilize torque-to-yield bolts, should I buy new OEM replacements or use ARP hardware?

I have Teleflex temp and pressure guages that I will also be installing.

Any other tips would be greatly appreciated. Many thanks in advance.

-Mike Malone
1991 Arriva, Mercury 150 BlackMax (0D0332289)

[91_Arriva_150]

Doing more searching:

Looks like most people like 35flt-lbs for the head bolts with motor oil lightly applied to the thread & washers.

Torque IAW - http://www.biggerhammer.net/mercury/....5_fishing.jpg

[hsbob]

one of the noted builder used the copper, but cant remember who. i tried it once but cant comment on if it was worth the effort.

[91_Arriva_150]

Update as of 8/6/12

- replaced both head gaskets and the exhaust manifold gasket. Old gaskets didn't look bad other than +20 of life.
- installed water pressure gauge (tied into tell-tale) and water temp gauge (cylinder head fitting)

At 4000rpm I have about 10psi water perssure and she still overheats after 20-30 seconds on plane. I was told 15/16 psi water perssure is typical when at cruising speed. Going to replace the pump and assocaited hardware. I am also going to be installing a set of side scoops(Mercury #17280A2) </SPAN></SPAN>

[91_Arriva_150]

Update 9/6/12

After replacing the water pump and fabricating a set of water pick up scoops (were on back order ad infinitum from Mercury) the motor would still over heat after being on plane for 20-30 seconds. Temp gauge would register 3/4 and rise. About 4/5 on the temp gauge, engine sensor would sound. Plenty of water pressure 16-20 psi.

I pulled the cover and when running at slow speed I observed that water was leaking from the poppet weep hole at rate of roughly 2-3 drips per second. So that obviously is not correct.

Once on shore I took the poppet valve apart (again) all gaskets sealed well and diaphrams looked in good condition but possibly not seated well. I took the assembly down and spoke to Bill the mechanic out at Fisher's Landing, AZ and he inquired as to where the poppet itself fit firmly or was loose in the mating hole and I noted it was firm fit. He indicated that poppet should fit loosley in that area.

He cleaned up the diaphram seat area and modified the poppet fins. He removed material from the fins, effectively reducing diameter of the poppet where the 4 fins are located. After paying for a new set of gaskets and leaving a healthy tip I went back to my place and re-installed the assembly.

Once back in the water, cruising in the marina the temp gauge again read 3/4 but once out on the river and up on plane the temperature gauge dove down to 1/4 and remained there as long I was on plane. This was the fix. Now I can pull wakeboarders, ski, and go for top end blasts just like normal and the temp stays solid.

Now with the boat back in functional order I have baselines where the new temp and pressure gauges should read. Hopefully this info will help someone else out there someday.

[EricB527]

Thanks, I will try it on my poppet valve…

[TEXAS20225]

you know the poppet valve is what cools your motor on plane right , thermostats go out of the picture above idle

[TEXAS20225]

it has caused me many problems over the years i rebuilt Merc v6 only for a long long time ( too long) even brand new ones have issues where vains become frictionus against the carrier in the gromet