86' 110 Johnson. Left side of block is cooler than right side.

[healey8390]

Hey guys. I had this problem when I first bought the motor and I found out it was only firing on one side so I replaced a powerpack and the cooler side warmed up to match the other side. The boat ran great after that and I've had it out three times without issue. After the last time I went out I flushed it at home and noticed a fuel leak on the plastic part of the line that connects the carbs where it feeds the primer solenoid. I replaced it today and it runs fine but lone behold the cooling on one side problem popped back up. I hit it with my IR thermometer and got 93 on the left side and 130 on the right. I checked spark with my timing light and it's firing on all four. To be certain, I ran the motor with the plug wires only connected to the left side and it did run. Then I checked compression and I'm getting 118-120 on all four. All plugs looked equally wet, a little too wet for my liking.

Is it common for a thermostat to fail open? Could it be something else like the deflectors? I'm probably reaching but I don't feel like doing t-stats on a bubbleback! In the end since it's an older motor I'd be served better doing the stats, head gaskets and deflectors anyway but I'd like to get some opinions. Thank you.

 

[emdsapmgr]

The 130 is probably close to a normal reading when idling. (even higher in warm summer lake water temps.) Normal summer idle temps would be 143-155 at idle. Yes, the stat can fail open, causing this problem. You will need to replace it. When you get the stat housing apart, check the nylon pressure relief valves also. Be sure they are not heat-deformed, leaking some add'l cooling water into the system on that side. Probably want to repl both stats as long as you have it apart. That's good compression for that year engine.