OB Overheating

[GCarlover]

Rich-V174SS, just wondering about your knowledge on OBs.  Ordered new thermostats because it's running ice cold on the Muffs. (After 5 min one side was lukewarm.)  They were stuck open.  Read this on a couple sites:  "If you perform your own engine servicing, be aware that an accurate temperature reading cannot be obtained while running the outboard on a flushing device. It has to be in the water for the pump, relief valves, and thermostats to operate as they were designed."  It used to run warm in the lake last time I checked a few yrs ago.  Running completely cold on the cylinder and head.(On the muffs).  They should be closed, right?  One open and the other 1/2.  1987 140 Johnson with 850 hrs.  New impeller last yr.  Rich

[Rich_V174SS]

Rich-V174SS, just wondering about your knowledge on OBs.  Ordered new thermostats because it's running ice cold on the Muffs. (After 5 min one side was lukewarm.)  They were stuck open.  Read this on a couple sites:  "If you perform your own engine servicing, be aware that an accurate temperature reading cannot be obtained while running the outboard on a flushing device. It has to be in the water for the pump, relief valves, and thermostats to operate as they were designed."  It used to run warm in the lake last time I checked a few yrs ago.  Running completely cold on the cylinder and head.(On the muffs).  They should be closed, right?  One open and the other 1/2.  1987 140 Johnson with 850 hrs.  New impeller last yr.  Rich

I get conflicting views on this. I've seen some engines overheat when run on the hose but run at the proper temperature in the water. But, if you've got proper water flow up to the powerhead then the thermostats should still control the temperature whether you're on the hose or in the lake. If all else fails run the engine with the lower unit submersed in a leaf barrel.

[Jerry]

I only test in a stock tank. You can't tell if the pump is working right if you are forcing water in through a hose. I got this one at a garage sale, but I'm sure you can find one if you look. It also works as a great Keg Cooler for a party.

[MarkS]

If it's any help at all, the two OMC Crossflows I've worked with both acted differently on the hose and muffs than they did in the water.  Yes, the thermostats should still close when cold, almost all the water coming out the prop.  But on the hose when they open up they don't discharge out the bypass the same (not as much) as when they're submersed, probably due to lack of back pressure?

The '78 Erude 115 I'm running now was a bugger to get everything tucked back in when replacing the t-stat's and bypass valves!  They recommend you do that every year or two, but I think I'll wait until I see issues before tackling that job again. 

[V153]

probably due to lack of back pressure?

Correct. They don't run like they're sposed to on muffs. They need to be submerged.

[GCarlover]

Still waiting for thermostats from Wholesale Marine.  Two weeks tomorrow.  They said it was special order (10 days) from  the Manf.  Last year I ordered a gasket from Boats.net and got a needle bearing for a Mercury.  Last chance for them.  The ildle setting on my looper will be around 1800 on the muffs and 1100 - 1200 in the lake.  About 900 in gear; for anyone that sets it slow and then it dies when you launch it.