1994 or 1995 Johnson 250 V8 Ocean Runner Thermostat/cooling issue

Joined
Jun 22, 2014
Messages
17
I recently purchased a Johnson 250 V8 Ocean Runner from craiglsist (As my 1979 Evinrude 150 :( recently blew a piston.) It has a serial number but not a model number, I was on hold with BRP for 30 minutes on two seperate occasions yesterday attempting to identify my exact model number. I will keep trying different hours etc. But I am pretty sure it is either a J250TXEOR 1995, or J250TXERC 1994. This motor sounds completely and totally awesome!! When I first started it, it popped to life! The cooling system has some unusual hoses attached to it that I haven't been able to quite identify just yet.

My question is in regards to the Thermostat. When I first fired up the motor, the Port side bank was much warmer than the Starboard side Bank, which has me concerned. Also, the indicator was not spraying water out of it, so I turned it off immediately and promptly installed a new water pump/impeller(I was planning to do this anyways). On my test run the indicator began spraying immediately. My Port Side was still hotter than my Starboard side, so my next step was to inspect my Port side thermostat. I managed to break off a bolt head holding the thermostat housing #@$%! The rubber diaphram had two holes in it, I didnt test the thermostat, just replaced both that and the diaphram and new gasket....of course after going through hell to get that bolt out of the hole!

The bolt is a long story, I ll just summarize it by saying after breaking the tap off in the hole and going through 4 drill bits and about 4 hours of chipping away at the tap, I was successfully able to get a heli coil in there! I hope I dont have to go through that ever again!

So after all of that, I run the motor again, and still the Port side was hotter than the Starboard side, although it took longer to get hot. Next I inspected the T-stat on the Starboard side and found that there was no thermostat in there at ALL!!

I have read about people intentionally removing the t-stat, so now I am thinking the Port side might be OK, just compared to the cold Starboard side it seemed hot. My next step is to install a t-stat in the Starboard side and get a thermometer to actually measure the exact temp. Does anyone have a recommendation for measuring/monitoring the temp from personal experience?

Also, What affect will this have moving forward for the performance of this motor? I still need to measure the compression after running it, the motor sat for 8 months according to the person I bought it from. I did a compression test when I first bought it, before running it, the Port side is 125/125/120/120, the Starboard side is 140/125/125/115. Writing this, I realize I should check the compression #'s again after running it.

Thank You for your inputs,

​Matt
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
one of those temp infra red guns are a good way to read temp. About fifty bucks
shouldnt get above 70ish degrees celcius . Make sure you check at idle too as it can be hotter then that at full speed
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Do a good decarb on the motor and it should help the compression numbers.
 

175se

Petty Officer 1st Class
Joined
Mar 6, 2014
Messages
274
The stbd side seems to run a few degrees hotter than the port side, like boobie said do a good decarb, but being the courious sob that I am why is #1 compression that much higher? JMO.
 
Joined
Jun 22, 2014
Messages
17
I will do a decarb after I get the tstat installed, I have to wait for parts to be delivered now. For decarb, what is your preferred method?
 
Joined
Jun 22, 2014
Messages
17
I am also curious about that compression # being so high, I have looked for signs of water and havent found any. I heard that a cylinder with moisture would possibly have higher compression #'s because water doesnt compress. But I haven't heard an alternative theory to that yet....
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
I am also curious about that compression # being so high, I have looked for signs of water and havent found any. I heard that a cylinder with moisture would possibly have higher compression #'s because water doesnt compress. But I haven't heard an alternative theory to that yet....
yes thats how you blow up a diesel, if youre worried look at the piston head, if waters getting in itl look steam cleaned
 
Joined
Jun 22, 2014
Messages
17
That is good news, because the color matches all of the other cylinders, and the spark plugs look good too.
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Get some BRP Engine Tuner and follow the directions on the can to the letter.
 
Joined
Jun 22, 2014
Messages
17
I installed my Tstat and did a decarb. My compression numbers are all at 125 now except that one top cylinder at 140. I took my boat out for a test drive on the water and it was leaking a lot of fuel when I got back! The carberator on the cylinder with 140 was leaking a lot of fuel. I was able to stop the leak by draining the float bowl and spraying a bunch of carb cleaner in there. Does it make sense to have high compression because of the carb though????
 
Joined
Jun 22, 2014
Messages
17
Ffollowing up about the tstat, both banks are the same temperature now. I purchased an infrared heat gun and confirmed both are now in the 150's at idle, which is within the normal range. Took it out for WOT, and the temp is in the 140's, after stopping and removing cowling etc. Seems good to me! The Starboard side was definitely under heating. What would the damage be from it being run with one tstat missing? Is there anything in particular that I should be looking for?

Thank You All!
 
Top