70hp thermostat compatibilities?

[garry-in-michigan]

The service bulletins I have theoretically run from 1958 to 1971, but some of the early ones I recalled as interesting must have been thrown out as being no longer relevant. The highest numbers I see are in the nine hundrads. . . 😎

[johnyrude200]

I was able to find a copy of SB 2221, it explains how the heat sensor in the head can cause the motor to go into SLOW mode when the engine is used in water that is above 70°.

Well the river water is currently at 74°, and the motor keeps going into slow mode when left at 4800RPM or above for much more than 10-15 seconds, yet it is not overheating. I have checked in with both a regular prop and test prop and been able to reproduce the same symptom both ways.

Don and Dan have been very helpful, so as not to hyjack my own thread, but it seems I need a new sensor to rule that out as a culprit next. Just glad it isn’t due to aeration on my boat, that would have been disappointing because I can’t change the boat!

[dan-in-tn]

Sorry Joel, just finished packing for Tomahawk! They changed from a solid brown sensor wire to a brown with blue stripe (higher temp setting). In some cases the horn would go off before the engine was considered to be over the threshold for an overheat.
I probably have a blue stripe sensor out in my junk drawer. I’ll have to check if I can remember before we leave in the AM.

Dan in TN

[johnyrude200]

I scavanged a blue/brown sensor off a 50hp motor ai had here. So that stopped the SLOW mode situation but now the motor is simply shutting off randomly at different RPMs.

Don had recommended I change plugs to QL77JC4s to rule out interference but unfortunately that doesnt seem to be the problem.

I have a new stator and pack in the mail, they seem to be testing out OK but that doesnt mean they are of course.

Certainly an ignition issue IMHO at this point. Motor starts easy and runs fine otherwise but has been erratic since day 1 with the ignition. My tach was spinning like a pinwheel and its never done that before, but the battery is charging normally.

It is not overheating. Its running just right at 130-145 at
Idle and drops to 105-115 at higher RPM.

[fleetwin]

OK, seems like the sensor with the blue tracer has solved the SLOW condition. You still have a random ignition miss and a crazy tach…
I don’t think the two situations are related, doesn’t seem likely you have a bad ignition charge coil and a bad alternator winding, but anything is possible. Does this engine use the simple three wire rectifier, or does it have the big ol aluminum regulator rectifier? It seems like the 1990 models still used the simple system with the three wire rectifier, can’t remember though. Joel, you were mentioning something about a stray lead on the back of the tach that you grounded to the aluminum frame that seemed to calm the tach down…Anymore info on this?
Sorry to be absent here, been battling a no hot water situation….I feel like the three stooges, down stairs banging on pipes and cursing….

[johnyrude200]

After switching sensors the SLOW issue went away, but now the motor shuts off randomly. Prior to the sensor change it would shut off and come back on randomly.

This would not happen at idle.

Rectifier is the simple triangle 3 lead style. I switched tachs and the new one seemed to work correctly but still went haywire a few times.

The original tach had a 4th lead which after looking at a few others appears to be power for the trim guage if connected. Not sure why grounding it somehow made it work better in this situation but it still wasnt reading accurately even with this band aid.

Hope your hot water comes back but at least with the heat wave it has to be luke warm still in the pipes!

[fleetwin]

Finally got it running by replacing one of those damn Taco zone valves…The Weil Mclain hot water tank uses the hot water from the boiler to heat up the water instead of having its own gas fired unit…
Unfortunately, looks like the expensive water tank is weaping a bit…Hoping this is just condensation, but that is not the kind of luck I have…
Post some pictures of that tach wiring…

[johnyrude200]

Old thread but wanted to provide a conclusion/update. I replaced the stator with a new unit and everything is working as it should now. My tachometer isn’t going haywire and the 4th lead need not be grounded, the motor is not shutting off randomly either.

Once again, testing numbers may show good results but that isn’t always the full story.

[Author]

Posts