1972 mercruiser 165hp inline6 overheating

[kobe24]

hey guys, im brand new to the forums and a brand new boater. i jus bought my first boat, an old 1972 bonanza fishing boat and i took it to a lake to test it out. well was in the water for like 2mins and saw the temp gauge reach 200. a little smoke was comming from the engine also. turned around and went back home

so from researching i found out it might be an impeller problem ,thermostat or water pump. i have some mechanic skills and would like to do this myself but am new to this engine. i also have to do an oil change to her.

can anyone pls point out where all these parts, or pls chime in with any suggestions. thanks!

p.s. if someone can send me a link to where i can find a servic manual that would be awesome!

 

[kobe24]

Re: 1972 mercruiser 165hp inline6 overheating

bump...

 

[redjmp]

Re: 1972 mercruiser 165hp inline6 overheating

Replace the impeller first. They go bad after 2 or 3 years whether or not they get used.

Chances are good that will fix ya!

If not then its time to take the riser off and have a look for excessive corrosion. Riser are a maintainence item as well and need replacing every 5-10 years...

Manifolds generally speaking last a little longer than risers but also must be replaced after about 10 years.

Unless you see the water pump leaking or hear the bearing sqeaking or rattling, then it is generally ok unless you run in saltwater in which case you need to check that the vanes inside haven't rusted away.

Thermostat would be the last thing I check as in my experience I have never had one go bad in anything!

Oh and if thats a plastic inline fuel filter you have there, then it need to be replaced with a metal one for compliance with the safety regs... or go BOOM!

 

[Bluestream]

Re: 1972 mercruiser 165hp inline6 overheating

There is a fuel filter under the cap on top of your fuel pump. You may want to check it, likely been there since 1972...

 

[dubs283]

Re: 1972 mercruiser 165hp inline6 overheating

Replace the impeller first.

not just the impeller...

replace the entire water pump assy AND the base assy and gasket

often times the base assy gasket fails at the aft and allows exhaust gases to enter the water pump at higher rpms

be sure to pressure test the drive after reassembly to ensure no seals are leaking

also, when the drive is off, inspect the entire transom assy, bellows, gimbal bearing, engine alignment, etc...

 

[ziggy]

Re: 1972 mercruiser 165hp inline6 overheating

if someone can send me a link to where i can find a servic manual

maybe someone else can. but to the best of my knowledge, the s/m have generally be deleted from on line due to copy write. that said, ya really gotta get one. it has the facts in it. for your '72, you'd want C-90-68648. it may come in 2 volumes. you'd need both. mercruiser will sell you one. best i know, about a hundred bucks. or i was successful on ebay for s/m 1 and 2.

so from researching i found out it might be an impeller problem ,thermostat or water pump. i have some mechanic skills and would like to do this myself but am new to this engine. i also have to do an oil change to her.

the impeller is the first place to look. it's located in the lower part of the drive. agree with others, the tstat and circ. pump are not generally the cause of overheats.
for an oil change, i use one of them siphon pumps down the dip stick tube. it's clean and easy to do, albiet a little slow unless the oil is real warm.

you've probably got a little work ahead of you. do a compression test so you have a base idea of what your working with.

in lieu of the s/m. ya might look at the winterize/summerize threads in the adults only sticky at the top of the i/o forum. go though those threads and you'll have a good start on putting her back into service.

as for that inline fuel filter, just get rid of it. they're not uscg approved. if ya really gotta have an extra filter, get a fuel/water separator. it would go in place of the in line fuel filter ya have and be uscg approved. the fuel/water separators are a good idea. though, personally i don't have one.

fwiw, i've had a '72 and a '75 L6 engine. both had to have the manifold and riser replaced. the '75 got water intrusion into the oil. i caught on quick and saved the engine via and oil change or 3 within the first 24 hrs. of failure.

be sure to use marine parts in your repairs. i know they are more expensive, but they are what you must have. auto parts are a no no on boats. most all peripherals on your boat engine are marine parts.

1st place to start with is get that s/m. it has the facts in it. wish i could help ya out with that.. but alas, mercruiser wants your money... imagine that..

lastly. ya've got a good engine there. from reading, the chevy 250 L6 is one of the best engines ever to be marinized for a boat... just a great work engine..

 

[dingdongs]

Re: 1972 mercruiser 165hp inline6 overheating

if you dissconnect 1"hose that runs between carb and rocker cover at the thermostat housing water should be flowing if engine is running whilst on muffs.this will initially give you an inclin if impeller is pumping.don't run 4 too long.report back.
manual you will find on yesterdays posts under 470 mercruiser

 

[dubs283]

Re: 1972 mercruiser 165hp inline6 overheating

manual you will find on yesterdays posts under 470 mercruiser

the OP has an inline 6 cyliner engine

the 470 is a 4 cylinder engine

the thread you are referring to is for a totally different engine and thus, a totally different manual

as stated, the OP needs manual #1

 

[EddiePetty]

Re: 1972 mercruiser 165hp inline6 overheating

......."Oh and if thats a plastic inline fuel filter you have there, then it need to be replaced with a metal one for compliance with the safety regs"...

And if memory serves me correctly, I believe the USCG requires metal fuel line between the fuel pump and carb.

While you're waitin' for a manual, click through the pages of this to help you understand some of your plant....
http://www.mercstuff.com/howdoi.htm

 

[msargius]

Re: 1972 mercruiser 165hp inline6 overheating

I have an inline engine like yours but the only difference is I have clossed cooling system, you have afresh water cooling system. the difference you will have a round cylinder below the exhaust manifold.

I fell for the same thing.... Had to change the riser, the manifold (will look good on the outside but was rusted and clogged on the inisde)....Water pump(impeller and base most propably shot)...also check if the water out passage in the lower unit behind the propeller is free and not clogged (mine was clogged and never cleaned) ....also check flapper (installed after the riser) mine was none existing (rusted out). Beware that sellers spray paint there engines to make things look good....for that age of boat which I own a similar one a 1973 but with no experience in boats I fell in the same trap....