any harm in back flushing ’67 Johnson 100 hp?

[boatman]

Hi,

Dipped the Lone Star in the water for the first time yesterday. Johnson V4 100 hp idled well at dock for a few minutes. Strong water flow out of the pee hole from start up. Just about to cast off and "hot" light came on. 2/4 (port side) cylinder bank was normal temp, 1/3 (starboard) bank was hot. Pulled the t-stat today and it looks like parts are missing from inside. I assume that is why I get a strong pee hole spray from start up. Any harm in back flushing this motor through the fitting where the starboard side of the t-stat hose attached to the cylinder head? Read somewhere that this will force water through the exhaust port into the power head, but have not seen a diagram and have no idea.

How do you try to dislodge stuff trapped in water passages, what is best way to back flush?

Appreciate all the help so far guys!

Paul

[dan-in-tn]

Its early AM here in TN and hopefully someone will be along to correct me if I am wrong, but V-4s won’t cool properly if thermostats aren’t in those motors and working properly. As I remember it has to do with balancing the water flow to both sides of the engine.

Dan in TN

[frankr]

Yeah, you can’t expect it to work if you throw the parts overboard. As for the back flushing you propose, it won’t hurt anything if you do it the way you said. Probably won’t accomplish anything either. You could throw a screaming cat through the water passages on that motor, so it is unlikely they are plugged up.

[boatman]

Frank and t2stroke,

Thanks for the advice. Who knows why it was taken apart and put back together without any of the innards. Lots of hose clamps on that S shaped hose going to the starboard side cylinder bank so somebody was trying to bandage it up. Maybe like me they didn’t realize that the thermostat will come apart with springs flying everywhere like a Jack-in-the-Box when you take it off. At least I found all the parts from the one off of the donor motor I am using. Will try and backflush since I have it apart anyways.

Frank, I have two cats at home. I’ll see if one of them would like to take a run through the passages and check for blockages 😉

Paul

[frankr]

I hear plumbers use a "snake".

[gjonz]

Hehehehe

[fleetwin]

There is supposed to be a spring loaded bypass in that thermostat housing along with the thermostat, the engine won’t cool properly if those items are missing as well.

[boatman]

Back flushed the cooling passages, looked like they flowed water pretty well. Put in the replacement thermostat. Will get it on the water tomorrow for a test.

I put two of the thermostats from donor engines in a pot of boiling water. One plunger moved a little, one didn’t seem to move at all. Also one plunger rod comes out of the thermostat completely. The other one seems to be attached. Is this normal? I put the one with the detachable plunger rod in the motor and buttoned it up.

Thanks,
Paul

[boatman]

Replaced the thermostat, dropped the Lone Star El Dorado in the river today and…. it fired up and ran well. Pulled out from the dock and got it up on plane easily. Only issue was that the steering is reversed! Had to dodge a barge and tried to steer left, boat went hard right almost onto the rock lined shores of the shipping channel. Holy crap! I changed the teleflex sytem from a rear steering bracket to a front steering setup by fabbing up a bracket to mount in the splashwell. Didn’t realize that now the steering is reversed.

Pumps water great, planes out nicely and cruises at about 29 mph. Ran about 17 miles on the Cal Sag shipping channel towards downtown Chicago, repeating the mantra "left is right, right is left" and made it back in one piece. Drinks petrol like a drunken sailor- burned about 7 gallons in a little over an hour on water even with throttle pulled back to 3/4. Is this what you guys get?

Anyways, really happy the motor runs, the impeller pumps, boat doesn’t leak after I sealed seams with Gluvit and bucked rivets and plugged the through hull holes from the old marine head. Had a great day.

Really appreciate all the advice. Thanks Frank, Dan and fleetwin!

[fleetwin]

Yeah buddy, these old engines really drink the fuel, your results seem normal for that vintage/style of engine with the big ol 4bbl carb. I know that the recommended fuel/oil mix for that engine is 50:1, but I would double it and use 24:1. In other words, use 1 quart of TCW3 outboard oil to 6 gallons of gas.

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