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C

carogator

Regular Contributor
Sold as a 1994, marked as a 4HP. ser.# OD90096C..Mercury
Does this motor have a thermostat? At the bottom of the
driveshaft housing,opposite the propeller, there are two small
half-round holes, that blow air bubbles out when running. Water
stream starts as it warms up, and stops for a short spell, and starts again.
doesn't seem to get hot. But I thought it should put out water continually.
Any help would be appreciated. Doesn't show up in the ser.# listings.
 
Last edited:
I'll see what I can tell you about your motor.

By the production number (serial) I make it as a built in late 1992 and probably sold as a new 93 model. BUT since the year of mfg is not encoded in the serial, it absolutely could have been sold as a "brand new" 1994 model if it sat around a couple years after it was built - I (personally believe) Merc did that on purpose so they wouldn't have "old stock/out of date models" sitting in the showroom.

I believe this model, and it's sister the 5 horse, were built by Tohatsu for Merc - they have a Japanese style carb and ignition system which Merc never used on their own designed/built models. This would be nothing new. For years Yamaha built major components and total motors (some Mariners) for Merc. After a falling out, Merc entered into a joint venture with Tohatsu and Tohatsu now builds most of the Merc 4 strokes under 40 horses in power.

Anyhow, there is no thermostat listed or shown in the parts lists/diagrams for this model as far as I can see. I don't have a service manual for this model as it was not included in the master set covering your possible model years (which reinforces to me at least that this was NOT a Merc built model, simply Merc "branded").

I'm not sure which "two holes" you are referring to from your description of where they are located. There is a strainer on the underside of the cavitation plate (so directly above the prop, but on the underside of the plate) where water is "sucked in" to water pump. Given that there does not appear to be a thermostat an inconsistent water flow from the tell-tale (may) indicate an issue somewhere in the system.

That could be anything from the impeller, to any of the gaskets/seals on the water pump cover - a compromised water tube, partial blockage somewhere in the tube itself or the water channels in the power head etc. If the bubble you note are coming from the pick-up tube strainer that would further reinforce that it's either not pumping correctly, or a seal somewhere is compromised and all the water is NOT being directed to the powerhead.
 
The reason your serial# comes up blank is because it's wrong. Newer Merc serial#s are always a 0 or a 1, followed by a letter, followed by 6 numbers (never a letter at the end). So.. with my Sherlock Hemlock wisdom, I figured that the C at the end might be a zero with a little bit missing. Ran that number, and she comes up as a 1992 4 hp.:cool:

No t-stat on this outboard, and I can't picture the 2 holes you speak of- could you post a picture? Intermittent water flow could indicate you need your water pump serviced- when was the last time the impeller was changed?
 
Document (1) (Small).jpgHey, thanks guys, upon closer examination with plenty of light, it is a 0 at the end
of the number. This motor was supposed to have set up at least a year. I saw it
run and pump water as described. Did the same at home. He said he changed the oil in the foot that morning, but I think he may have been covering something up. Today, while
checking the numbers, I saw white emulsified oil collected on the foot where it sat in the
water. Hopefully is a drawing of where the holes are that are blowing air bubbles.
They are at the line where the drive shaft housing and lower unit bolt together.
Thanks
 
Okay, thanks to all who responded. Time to start opening it up,and see
what is going on. Seems it may not be anything major, so it will worth doing.
Again, Thanks. may take a couple weeks but will report findings.
 
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