1986 110HP Crossflow Help With Stuck Thermostat Needed

[mrmamiller]

I have a 1986 Johnson 110HP crossflow V4 (bubbleback). Got boat out of winter storage and on first fire-up, starboard side overheats. I shut it down before the alarm. Running on muffs in driveway for blowing out the fogging oil and quick check out. Port side is cool 110 DegF (water is cold well water). Starboard side gets to 155F and climbing, the point where I kill it. I know that on first fire up, these things happen, and usually once restarted, problem goes away. I have gone through the shut down/fire up sequence 4 times to no avail. I changed the thermostats and poppet valves 2 years ago and have had no problems at all since. I regularly monitor motor temps with affixed thermocouples and no problems have been seen. This hot starboard side temp has been measured with thermocouple as well as IR gun. Results match. The hose port where the hose exits to the thermostat is cold. The thermostat housing is cold. I assume that there is no hot water getting to the thermostat so it can open. FYI, when doing the thermostat job 2 years ago, I cleaned/slightly enlarged the bleed hole in the adapter plate to help alleviate this sort of issue. Pee stream is strong

So, any quick fix that I can do so I am not going through that horrible T-stat job again?

 

[mrmamiller]

Re: 1986 110HP Crossflow Help With Stuck Thermostat Needed

UPDATE: I decided to remove the short hose section between the stbd head and the T-stat and connect a piece of plastic tubing to the port on the head, allowing water to flow freely through the heads while running. Water poured out of the disconnected short hose segment which was still connected to the T-Stat housing as well. After running for a while, the port head temp came up as far as could be expected (120F) and the stbd side remained cold (102F) with no restrictions. This was for a period of 10 minutes at idle speed. After putting the hose segment back in its normal position, the temp on the stbd side no longer overheated. There is a temp imbalance and they are not at their usual temps, but this will clear up when I put the boat in the water (past experience). So, short term, I think I am out of the woods. Any thoughts to pass along as to what happened to cause the problem in the first place and how to prevent it in the future? (And I'm going to carry a section of hose or two with me when I stray far from home with the boat).

 

[emdsapmgr]

Re: 1986 110HP Crossflow Help With Stuck Thermostat Needed

Once side can overheat if the stat sticks shut. I'd probably pull the housing apart and replace both stats, just for good measure. Best not to overheat when 2 miles from the launch ramp. I know these bubble backs are a pain, but it's a prudent thing to do. Check something else when you get the housing apart. The plastic center body in the thermostat housing (called the valve body) has small holes in it to pass water to the backside of the stats so they will heat up and open. There were two versions. Starting in 78 up through maybe 85, there were two pinholes. One would feed each stat. They are very small and can plug up with dirt, debris, sand, and prevent water from reaching the back of each stat. If one plugs up, that side of the block will surely overheat, even with new stats. Somewhere around 86-but by 1992, the valve body was changed by the factory. The two pinholes gave way to a larger, single hole which would feed both stats and not plug up as easily. Not sure which you have, but check your valve body to be sure water can flow thru it. The factory changed the design, but not the part number of the valve body. The picture is the later valve body with the single hole.