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1978 model 700 70 horse mercury thermostat

D

Dave T

New member
I have a 1978 Mercury model 700. Does this motor have a thermostat? I have a service manual but it covers a lot of different years and models and shows most motors with thermostats to have a small cover over the thermostat and pressure relief valve that this motor doesn't have.
 
You must post serial # for Mercury motors.--------My info shows a thermostat and poppit valve one for the 78 models.
 
The serial no. is 4980812. It looks like it may have a thermostat and relief valve under the exhaust cover but I would probably want to get new gaskets before removing it. What is the best way to check if the thermostat is working? this motor seems really cold blooded and takes a long time to warm up. What temperature thermostat should it have?
 
Thermostats are often removed for some reason.-----------Order those gaskets and if it is a fresh water motor it is not hard to do do this project.-------Thermostat is usually in the 145 degree range.
 
Thanks for the replies I checked the info under exhaust cover and parts for serial numbers starting 45 to 55 and it shows a thermostat and relief valve for these motors with serial numbers starting below 48 but not for any above this. Now I'm more confused.
 
Thanks for the replies I checked the info under exhaust cover and parts for serial numbers starting 45 to 55 and it shows a thermostat and relief valve for these motors with serial numbers starting below 48 but not for any above this. Now I'm more confused.
 
Most of the dozen or so Merc triples I've messed with have had their thermostat removed by the dealers. This motor uses an impeller way too small for it, resulting in burnt top cylinders. (All but one of them above had that problem).

So...if it does have a t-stat, you might consider removing it.

Jeff
 
Thanks for the replies guys. From what I've looked at on this site it looks like they did away with the thermostat and relief valve at serial number 4825248 maybe for the reason fastjeff mentioned. Since this motor is 36 years old and has good compression and runs good I won't worry about it. I've installed a new water pump, new switch box, cleaned and rebuilt the carburetors and repaired a lot of the old wiring.
 
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