1986 Johnson 150 V6 Thermostat Replacement

[Terrapin]

One side of my engine is running cool. My diagnosis is that the thermostat must be stuck wide open. Am I missing any other root causes?

Reviewing my OEM service manual for thermostat service, it seems to be a relatively simple replacement operation. My question is, "is it necessary to replace the pressure release valve seat and washer?" I'm trying to avoid having to remove the cylinder head cover. While I have a torque wrench to reinstall it properly, I'm just trying to get a feel for whether this is an item that gets damaged and should be replaced to be prudent, or can I shorten the job up by eliminating this step. Let me know your thoughts, I will then order my parts.

Lastly, where can I order a small tube of OMC Gasket Sealing Compound?

Thank you,

 

[boobie]

Re: 1986 Johnson 150 V6 Thermostat Replacement

If the pressure relief valve seat and ect look good, leave them in.

 

[Terrapin]

Re: 1986 Johnson 150 V6 Thermostat Replacement

To clarify, I can easily get to all of the thermostat and pressure release valve components except for the pressure release valve seat and washer which I must pull the cylinder head cover to get to and inspect. I'm trying to understand whether the pressure valve seat and washer are a functional concern or are they robust enough that I can eliminate pulling the cylinder head cover to replace?

 

[boobie]

Re: 1986 Johnson 150 V6 Thermostat Replacement

Has the mtr ever been overheated ?? If not leave them in.

 

[Terrapin]

Re: 1986 Johnson 150 V6 Thermostat Replacement

I finally got around to changing out the thermostats and pressure relief valves. I replaced all the components under the thermostat cover except for the pressure relief valve screw and the pressure relief valve seat and washer which are under the cylinder head cover.

After performing the service and prior to leaving on vacation I splashed the Whaler in the local river and fired it up from its winter nap. There was lots of angel hair like weed that may have got sucked against the intake which shortly into the test gave me a scare with no water pressure and temperature increasing. Revving the engine brought the temperature down to what I thought was the new normal.

Running on the cleaner bay water on vacation, the overheat alarm came on after about 45 minutes of running at about 3000 RPM. I shut it down, let it cool and limped back at slow speed and no alarm. After the service, the:
Water pressure gauge is reading 2 PSI at low idle of around 1000 RPM.
Water pressure increases to 8 PSI at about 3,000 RPM
Temperature gauge is reading higher than before, but it seemed one of the old banks was running cool which prompted the service.
I have a tell tale, can’t say it’s strong, but it is not weak.
I am due for a water pump kit change, but I am seeing the above water pressure and tell tale. Is the water pump the problem, or do I have the wrong thermostats (BRP P/N 5005440) or something? The new thermostat seemed to be longer in length.

I may have placed the thermostat grommets on backwards, would that be an issue?
Given the water pressures, and higher temperature tripping the warning horn, any thoughts on how I can salvage the vacation? Should I throw the old thermostats back in? Can I salvage the new gasket I just put in, or should this be replaced if I change the thermostats? Should I pull the thermostats until I get home to change the pump out?

Any thoughts/solutions would be appreciated.

 

[Terrapin]

Re: 1986 Johnson 150 V6 Thermostat Replacement

I pulled boith thermostats and both pressure relief valves. I left the thermostat covers off and started the engine (in water not muffs) to insure water was pumping thru both heads. I had water flowing out of the open thermostat cover area.

I reassembled leaving the thermostats out. I'm now running ok with approximately 95 degrees on both heads while idling and 130 degrees after running at 4500 RPM. Temps were measured with IR thermometer.

I tested the two old thermometers and two new thermometers for function on the stove and all four seem to be functrional and open fully around 145 degrees.

Do I have a restriction from salt build up or is my water pump impeller getting weak? What should I look at next to enable me to install the new thermostats and prevent over heating? Will running with out thermostats resultin more carbon build up?

 

[emdsapmgr]

Re: 1986 Johnson 150 V6 Thermostat Replacement

Normal water pressure would be 6-8 lbs at idle. Nearly 19-20 when you are blasting down the lake. You really need to run that engine with both thermostats. Without stats that engine will run cool. Cool running crossflows tend to accumulate carbon around the ringsets/piston skirts quicker than engines running stats. That engine should idle at 145-155 degrees. Once on plane, the pressure relief valves will open and the temps could go down 20 degrees or more. Put the stats in and do a test run. Check the telltale nozzle in the cowling for a possible restriction.

 

[Terrapin]

Re: 1986 Johnson 150 V6 Thermostat Replacement

emdsapmgr, Thanks for the reply. While I can throw the thermostats back in, I really haven't changed anything, since my overheat alarm incident, which would give me any confidence in a different result. Unless, running the engine for a few seconds with the thermostat covers off purged the system?

Regarding the pressures you mentioned, I haven't seen anything in the past 10 years over 10 psi with the current new Teleflex water pressure gauge or my old OMC gauge. There was even a new water pump installed 6 years ago. However, all of these gauges seem to provide relative readings.

I read something about diverters being damaged or collapsed in a separate thread. Would that be a possibility?

Also, I seem to have a steady tell tale stream. Are you thinking it may not be fully opened and restricting the water flow through the engine? I was thinking that it is only a tell tale and it didn't represent all of the water volume going through the engine block. Am I wrong? I'm just trying to understand. . .

 

[Fed]

Re: 1986 Johnson 150 V6 Thermostat Replacement

I read something about diverters being damaged or collapsed in a separate thread. Would that be a possibility?

Yes.

 

[emdsapmgr]

Re: 1986 Johnson 150 V6 Thermostat Replacement

The telltale nozzles can/do plug up with dirt, sand. The visual appearance is that there may be a problem in the cooling system, when it's just a minor restriction in the nozzle. You obviously have both a water pressure gauge and a telltale. Do you have the telltale line "T'd" to run both the gauge and the telltale? You might just plug the gauge hose to the telltale hose barb. (disconnect the telltale line.) See what pressure the gauge reads. Sometimes a t'd line will cause the gauge to somewhat lower, as some of the pressure bleeds of to feed the telltale. Over the past many, many years, I've had more than one water pressure gauge go bad over the winter. If there is any residual water in the gauge in October, the freezing temps destroy the bladder and the mechanism inside. Once that happens, the gauge will read, but it's always 10 lbs off. You've tested between two gauges with same results, so that serves to validate your low pressure readings. Pretty unusual.

 

[Terrapin]

Re: 1986 Johnson 150 V6 Thermostat Replacement

Normal water pressure would be 6-8 lbs at idle. Nearly 19-20 when you are blasting down the lake. You really need to run that engine with both thermostats. Without stats that engine will run cool. Cool running crossflows tend to accumulate carbon around the ringsets/piston skirts quicker than engines running stats. That engine should idle at 145-155 degrees. Once on plane, the pressure relief valves will open and the temps could go down 20 degrees or more. Put the stats in and do a test run. Check the telltale nozzle in the cowling for a possible restriction.

Can you explain how the pressure relief valves open up on plane? I was thinking that these remained closed unless the engine overheated and built up enough pressure to overcome the pressure relief valve spring. It just seems like it would take a lot of pressure to open it up at a higher speed and water pressure???