1985 merc 9.8 thermostat/cooling question

[green4themoney]

I recently picked up an exhaust cover kit with the thermostat for my 9.8, it puts a plug where the old telltale elbow comes out of the water jacket cover, and now the water for the telltale exits at the top of the thermostat cover, but now water only exits kind of intermittently, so is the telltale water only exiting after the thermostat is open? I felt the exhaust cover, felt pretty cool, and the motor runs greater at low speeds, doesnt load up at all! like it used too with straight water... also could i put the blank off plug in the thermostat cover and just use the old telltale so ill see a steady stream? Or will this cause the thermostat to work incorrectly? Also the water coming out was pretty hot....

 

[Texasmark]

Edit: I just re-read your post and realized you already have a port on your new exhaust cover. Great. Use it and cap off the tube from the stat for the reason stated below.

Telltale tube is much smaller than the stat opening so I'd expect it to be a parallel path. If you don't have an Ell there already, drill and tap a ⅛" pipe thread in the exhaust manifold cover being careful as there are 2 plates there to form the exhaust cooling water channel. Tap into that with an Ell threaded on one end and hose barb on the other and plumb that over to your trell tale fitting. You'll have water as soon as the engine gets charged with water.

I'm with you. I think Mercs idea to tell tale off the stats was stupid! Late 1990's 150 V6s were plumbed that way too.....sitting around waiting on your stat to open.....will it or won't it....is is too cold to open? Do I even have water pressure to the engine? How long am I supposed to sit at the dock and wait for the stat top open? Maybe it never will............

Edit: On the above statements....looks like Merc came to their senses.

Some smaller engine stats open at 125F (who knows why) where as the larger engines run 143F to open. The hot water heater in your house in the Normal position puts out 140F for a reference as to what's hot and what's not. Over temp alarm on larger engines is 195F for a number to figure how hot you can get before you have a problem.....since 212F at STP is boiling, 195 is steaming, not to be confused with warm water (vapor) on cold mornings.

Edit: Don't know if a 9.8 has an OT alarm, especially if it's tiller without electric start and battery connections.

 

[green4themoney]

I dont know im tempted to give up altogether and sell the engine and just see if i can find a yamaha, the motor calls for a 143 degree thermostat, it almost seem like its overheating at mid throttle.... startslsing a bit of power, than i pulled the stat, doesnt seem to be losing power but motor loads up cause its running too cold at lower rpm.... should i see if i can find a 123 degree thermostat, do you know the part number?

 

[flyingscott]

Actually having the tell tale off of the thermostat was a great idea. You know exactly what is happening with the cooling system. The V6 motors were fine just give them a little gas and they would pee. I suspect you have a blockage somewhere. Have you tried running the motor with the thermostat and cover off how much flow do you have? You should always have a spray out of the pee-hole, because the thermostat should have a small bypass hole. Does it? Are you running this in a barrel?

 

[green4themoney]

The new thermostat doesnt appear to have a "weep" hole, but seems to mist or bypass a little bit upon start up, if i pull the stat i get continuous flow even at low idle, im a little confused as to why mercury didnt use a thermostat on all 9.8s after the fact, just seemingly a select few? And am i missing another part possibly that compliments the thermostat set up?

 

[flyingscott]

Because the original motor design dates to the 50s. Look up your serial # to make sure you have all the parts. It is going to run hotter overall. Have you tried adjusting the carb because those motors ran a long time with no thermostat needed. Are you running the correct plugs? Is the choke opening all the way? When was the carb serviced last?

 

[racerone]

On severe overheat the plastic washer at the TOP of the water tube melted.-----Folded over and blocked water flow to the engine.----Factory replacement part is an iimproved material.

 

[green4themoney]

I serviced the carb last year, put a fuel pump with all of the goodies, tried the low speed mixture screw, the motor has no issues at idle or wide open throttle, just quarter throttle to half, seems to load up or "four stroke" choke is working great, stays open perfectly unless i move it, i do have the correct plugs (B9HS 10) and ive tried the buhw-2 perma gaps both seem to run with different characteristics.....

 

[flyingscott]

Post #7 may have your answer

 

[green4themoney]

Thanks for all the help guys, i replaced that washer last year when i rebuilt the engine, i changed the water outlet to the water cover jacket and plugged off at the thermostat and this seems to be working the best, i tested for a while no overheating and seems to be keeping the heat in so im a happy man, ill take a pic of my set up today!