150 Saltwater Thermostats

[NOLA26]

I have been reading up on all of the little tricks people have done to keep their motors up. One thing I keep seeing when it comes to the tell tale output and/or water pump, is to "gut" the thermostats. I understand the tell tale is down stream of the thermostats. I just replaced the entire water pump- housing, impeller, gaskets, etc. When I start the motor the tell tale doesn't start peeing until I raise the rpm's. I keep reading about gutting the thermostats, but I can't find a "how-to" detailing the procedure. Can someone shed some light on what exactly needs to be done? I am assuming this procedure keeps the thermostats open all the time so the tell tale is always outputting a stream, right? Thanks for any help.

 

[Dukedog]

some in "southern water" get away with gutted stats but if they were meant ta be that way merc would produced 'em that way.. if anything with tha motor doesn't perform as it should straight outta tha box then something is wrong with it.. tha "peeing thing" at idle can vary with motors.. not all will do tha exact same thing.. as long as you don't get an over temp alarm there shouldn't be any problem or worry...…….

if ya bound n determined ta do it its simple... pair of dikes, snip, snip and done... but merc makes replacement restrictor "washers" with different size holes in 'em.. one is 1/8" for high perf stuff and one is 3/8' for more "production" stuff.. just keep in mind these are for use only if ya know what ya doin' and/or lookin' for a specific results...… jmo

jan.. a water pressure gauge is really a must as far as i'm concerned for tha water stuff... it will show pressure at idle even when no "pee" there on "production motors".

 

[Sea Rider]

Peeing port which shows water pump is working and thermos are independent systems from each other. Rremove the rubber hose that exists the powerhead if having one. Insert the red cannula of a WD-40 or Carb Cleaner can and spray an overdose of product, let soak. Run cannula back and forth to help clean any water obstruction if any, also check outter hose for water obstruction.

If with no avail, there's already a salt build up inside the powerhead where discharges water through the peeing port directly or by means of a rubber hose. Try a long OB flush with Salt Away using a barrel. You can remove thermostats, soak them in pure vinegar for 30 minutes and brush off with a hard bristle toothbrush whatever is building on them to keep them clean and OB cooling nicely.

Happy Boating

 

[Chris1956]

Not all Merc V6 motors are plumbed exactly the same. However, a lot of them will not have a telltale until the motor warms up and the 'stats open. On a garden hose and flusher, this may not occur,unless idle speed is increased to add some load to warm the cooling water.

At about 1500-2000 RPM the water pressure is high enough to push the poppit valve open, adding to the cooling water flow.

The stock motor cooling system design is a good one. I am not sure why you want to change it. I would recommend a water pressure valve with a 0-15PSi scale, be plumbed into the cooling system.

 

[Texasmark]

I assume "gutting" the TS is analogous to just removing it. On some engines, like Merc V6 blocks (late 1990s 150 for a reference) the pee is plumbed off the output of the stat meaning the engine cooling water has to get to 143F to get the stat to unseat and let water out. This means that initially you have to wait for it and then when it first comes out it's on and off as the engine warms up.

Other engines are plumbed directly and as soon as you get a few # of water pressure you get pee. Changing from the former to the later on those engines is no big effort and I did it because I didn't want to wait.....just tapped into the bypass valve feed hose instead.

On removing the stats, or modifying the block cooling water per se, on the mentioned V6 and other engines surely, the stat is at the top of each cylinder bank and if you pull them out, and let water free flow, the top cylinder on each bank doesn't get fully covered in water at engine speeds below 2500 rpms (serv. manual number). Above 2500 water pressure (when the proper stat. is installed) is sufficient to force the bypass valve (popoff) off it's seat and allow full flow through the powerhead.

Side note: The engine in my Avatar, 2002 90, triple, looper, was purchased (with the boat) 2 years old. On my maiden voyage, I got out past the "no wake" zone and was putting around getting used to things and the Over Temp. alarm sounded. Didn't know what to do so I decided to punch it out to get some "ram" water assist to the impeller and once up on plane, a few seconds later it extinguished. Didn't reoccur until I slowed back down (below 2500 rpm). Short story....my stat was stuck shut (failed) and the bypass valve kicked in at the higher rpms as was it's design.

If I were operating in salt water, a new stat(s) would be an annual maintenance event!

 

[Chris1956]

Mark, I think you took a large chance running that motor. Not sure what "Ram" water is.

JMO

 

[Faztbullet]

Peeing port which shows water pump is working and thermos are independent systems from each other. Rremove the rubber hose that exists the powerhead if having one. Insert the red cannula of a WD-40 or Carb Cleaner can and spray an overdose of product, let soak.​

Nope...… Spraying lube up the line will just wet t-stat or run out into adapter plate and out exhaust.

 

[Texasmark]

Mark, I think you took a large chance running that motor. Not sure what "Ram" water is.

JMO

It ran at home ok on the water hose in pre checks before I took it out for it's maiden voyage. Water pressure was apparently adequate to unseat the popoff valve and get adequate engine cooling at idle and a couple of revs.

Ram water is ram induction water driven into the water inlet ports on the front sides of the lower unit as a result of boat speed. Same kind of air pickups on aircraft for the same reason. Between that and the rpms, the displacement water pump becomes a centrifugal pump as the impeller blades fold back.....per some text I read years ago in a service manual.

 

[Faztbullet]

There may be a little ram pressure but its not that noticeable.. If so water pressure gauge readings(PSI) would continue to increase the faster you go to a point gauge is pegged... JMO

 

[Texasmark]

There may be a little ram pressure but its not that noticeable.. If so water pressure gauge readings(PSI) would continue to increase the faster you go to a point gauge is pegged... JMO

I don't have a pressure gauge so I couldn't elaborate on that. Info on impeller blades comes from Merc. publications,,,,forget just where. Considering the shape and location, gotta be designed like that for that reason. Otherwise would be just holes in a flat plate on the side of the LU like the old OMC bullet LU. (opinion).......buttttt their water pickup on that LU was attached to the antivent plate and on the leading edge of the exhaust casting was the screen wire covering the water inlet.....right where propwash would force water into it and generate water pressure to aid in cooling at the higher rpms. (opinion)