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Engine Thermostats on Honda 150 HP OB

S

Senior Ron

New member
IS IT POSSIBLE ? For a defective thermostat to affect the computer and cause the engine RPM to fluctuate (or vary) approx. 300 RPM at 2000 RPM engine speed. If not, any other possible causes for this to occur.v
 
Electronics can get damaged from excessive heat under the cowling, What makes you think or know thermostat is defective? alarms? Lights on? Codes?
 
Thermostats would probably not cause "surging". But, of course, they do need to function properly for the engine to run efficiently.

It's more likely the carbs are out of balance with one another. Or they need cleaning.

Or, if you have fuel injection this could be something like a faulty O2 sensor or MAP sensor.

In either case, It's going to require some diagnosis and the use of specialty tools like carb balance gauges or Dr.H in the case of fuel injection.
 
johnnygjr said:
Electronics can get damaged from excessive heat under the cowling, What makes you think or know thermostat is defective? alarms? Lights on? Codes?
Click to expand...

Thank you all for the replies and advice. Presently I have no lights or alarms. Diagnosed in the fall and no current or stored faults were found yet the engine surges at 2000 RPM. I only asked about the T stats possibly giving a false reading to the computer if so I can change the T stats myself before getting into more expensive diagnostics at the marina. Today I ordered 2 T stats/ O-rings....TBC......
 
Senior Ron, t-stats can be tested on the stove in a pot of hot water, they usually open up around 143 degrees and about 3 millimeters,If they check out,save them for spares! You can buy a infrared temperature gun for 20 bucks at harbor freight store to verify temp. on heads while she's running. A little more history on your engine would help us with your issue, Has it ever overheated? Does engine achieve w.o.t. Same fuel from last fall?
 
Post your engine year model and frame number. Hondadude might be able to tell you if there are any technical service bulletins or known pattern failures for this complaint on your specific model. If so, that might save you a bundle in diagnosis.

In the meantime, you might want to pull and inspect your spark plugs to possibly identify any issues there. As in; all of them gapped correctly? Excessive electrode wear? One plug looking "whiter" (lean) or "blacker" (rich) than the others?

Or, if all of them look blackened it might indicate an overall rich condition which, by the way, could actually be caused by faulty Tstats. In which case you may want to change the plugs out for some new NGK's. Still not likely to be the cause of your issue but it's something you can do yourself. The more you know, the better off you'll be if you end having conversations with a shop.

Good luck.
 
Almost forgot!
If your engine is fuel injected, there could be a problem with the VST. It needs to be drained and cleaned out periodically and the fuel filters serviced. Have you been keeping up with that?
 
Agree that you should post engine and frame number so Hondadude can see what you have.

On my BF 225, typically, if you are having a spark or timing problem, it affects the programmed fuel injection and will throw a code. A fuel feed problem will not typically throw a code, so I suspect you have a fuel feed problem.

Is the surging just around 2000 rpm, or does it occur at all ranges above 2000? If all ranges, the first thing to check is the high pressure fuel filter. If that has not been changed in a year or so, it's time to do so.
 
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