Running Hot

[Quadruplecccc]

Just dropped a rebuilt 351 w (233) in boat . Cam in motor is no longer stock ,(higher duration) Old motor ran at 150 degrees with same outdrive. This one runs at 190 deg. Does not go over that. Is it possible that this motor will run that hot or must I keep digging into this? T-stat was just replaced w/140 deg. Also replaced exhaust shutters. This motor had about 30hrs on it when purchased. What do you all think?

 

[Don S]

Re: Running Hot

Shouldn't run that hot. New thermostats do fail. Did you install a new raw water pump impeller in for your NEW engine? If not, do so, and inspect the pump itself. Nothing worse than overheating a brand new engine.

 

[Quadruplecccc]

Re: Running Hot

I'll be getting a new water pump kit for outdrive tomorrow. That being said, this is what I checked so far ;Pulled circ. pump and inspected. Nothing bad here., Pulled hoses off manifolds and ran hose water through, lots of flow. Since previous owner had run it for such a short time I don't believe there should be any blockage in the block. ( not ruling this out ). How much water pressure does the outdrive impeller put out? Could it be that the existing impeller pushed just enough water to keep old motor happy and does not have enough life left in it to supply new motor with enough . For a standard cooling system this shouldn't be this difficult to figure out but, its got me sratching my head a little

 

[Don S]

Re: Running Hot

If you did all that BEFORE checking the raw water pump, you are doing things Bass Ackwards.
The impeller is the first thing to check on an IO overheat. There are just too many things that can take out an impeller. Plus, if they are over 1 year old, they are suspect.

 

[Quadruplecccc]

Re: Running Hot

I agree I'm working backwards but I was working with a few unknowns. I know my lower unit was ok before engine swap, or atleast I thought. Had to check the things that the previous owner may have overlooked. What other test can I do If same problem shows up after water pump is replaced?

 

[Quadruplecccc]

Re: Running Hot

changed water pump and tried it again. Slow temp rise to 180* and then stopped. I just can't figure this one out. Elbows are nice and cool but the manifold start getting hot as compared to the elbows. I can feel the water pushing through the hoses if I squeeze them. I have all the hoses on the way my clymer book says to but it lmost seems as though the elbow hose and the rear manifold hoses should be reversed. This way colder water will be pushed into the manifold instead of flushing out the elbows with all that cool water. Any thoughts??

 

[P 0 P E Y E]

Re: Running Hot

The "new" engine temp sender, is it the one that goes with the gage?
just checking.

Does the engine actually overheat?

 

[Quadruplecccc]

Re: Running Hot

Well, the temp sender is an automotive type but seems to work ok. I wired my marine temp guage and they agreed with eachother. As far as actually overheating, I would say no. The fact that it wants to run at 180 to 190 has me concerned. Several of my motor head friends say it is not uncommon for a beefed up motor to run hotter than the original. This puts me a little out of my comfort zone because I'm used to my old motor.

 

[Quadruplecccc]

Re: Running Hot

Is it possible this motor has a higher running temp than an older motor and will cool down as it breaks in over time

 

[jtybt]

Re: Running Hot

What drive do you have? The type I has a different style pump and has always been more sensitive to wear out/going bad.

Didn't notice if you had FWC or raw water but with a 140*, I'd guess you have raw water. Check the risers. they are notorious for clogging because of the small water outlets in them. They need them small so the water will fill the risers water jacket before draining out.

Chances are, cuz they're cool to the touch, they are good, though.


180-190 is too hot for a raw water cooled engine. I'm not sure how far back the thermostat housing with the little balls went but they are critical to the water circulation thru the block. They were notorious for rusting up and not working.


Are you in saltwater by any chance?

 

[Quadruplecccc]

Re: Running Hot

50/50 salt and fresh water usage. Never heard of any balls in thermo. housing . Can you elaborate on this? 1976 233hp motor w/ standrd cooling and a #1 outdrive w/new water pump. Once again I hooked garden hose to manifolds and elbows and had plenty of flow . Circ pump looked fine , new thermostat (140*) still runs @ 180* @ idle.

 

[Quadruplecccc]

Re: Running Hot

Ok, I found something new! I discovered that there is a hole in the carb to intake gasket. Ran the motor a little and then sprayed wd-40 at base of carb and around intake gasket, Should have bogged or killed engine but, found that the wd was blown away from carb gasket instead of being sucked in. I should have lots of vacuum there, not exhaust blowing out. I'm thinking bad intake gasket because this would have been the last place previous owner would have touched and had the chance to damage the gasket. First I will have to check the compression to see if there is a bad head gasket or worst case a cracked head. Oil is clean. Which of these possibilities would fit my running hot condition? Thanx!

 

[jtybt]

Re: Running Hot

Hmmmm! Never ran across that problem...at least never did that test and have pressure instead of vacuum from the base of a carb.

Did you spray long enuff to see if it was related to valve timing...as in one or more valve was not seating/adjusted too tight? This may be your problem


A vacuum test would be real good at this time.

 

[Quadruplecccc]

Re: Running Hot

never did a vac. test. How do I get started??