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Johnson and towers 671 N Thermostats

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arielmiller

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I have two 1980 detroit diesel

I have two 1980 detroit diesels 6-71n which are running too cool even at cruise speed. about 160 F at cruise and 150 F at idle. Both are marinized by Johnson and Towers with N80 injectors. Does anyone have a part number on the thermostats to be used? Someone told me the correct thermostats are 173 F. Is this true? If thats the case the ones i have are probably stuck in the open position. Any input would be great.
 
"Hi, don't have any part n

"Hi, don't have any part numbers to offer but just wanted to point out that the 71 USUALLY utilizes "full blocking" type thermostats as opposed to poppet and or bypass type. You may very well be right that yours are stuck open but you must also consider that they may be the wrong stats for your housing. Also, the full blocking stats were used in conjunction with a set of seals press fit into the housing and, in many instances, the seals are failed or installed incorrectly."
 
Thanks for the input. Did jt c

Thanks for the input. Did jt change the thermostat housing or is this a detroit design and parts. The only Reason I ask is that the service center needs to know which part numbers to use. Apperantly getting jt parts for this engine is very tough.
 
"J&T usually can tell you

"J&T usually can tell you everything about your motors, Just call them with the serial numbers and they should have them in the computer. My 1980 Viking 671-N's came from J&T out of their Mount Holly shop in New Jersey. I gave them my serial numbers and they told me the day they left the shop for delivery to Viking."
 
I called them with serial numb

I called them with serial number and they told me they accidently threw away a bunch of files and my engines were one of them. Btw I have a 1980 viking aft cabin. Do u know what thermostats you have in your boat?
 
"I would think it is highly un

"I would think it is highly unlikely that they would alter the thermostat housing or the thermostats. They probably just needed to plumb in the heat exchanger. If you pull the thermostats, they will probably have the 7 digit GM part number stamped in the body and the temp setting will be stamped on the end of the piston wax reservoir if they are genuine DDC. You should also see the DDC "spinning arrows" on them if they aren't aftermarket."
 
"Ariel- I had a similar proble

"Ariel- I had a similar problem with my starboard 671 engine. Was running extremely cold at idle, even after cruise. Smoking badly and leaving a fuel slick out the exhaust port. After changing injectors and a compression test on each cylinder, still had the problem. I could only imagine that the thermostat was stuck open. Pulled it, found a piece of trash hanging it up, and swapped it out. Problem solved - and yes, it is a 173 degree stat."
 
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