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1977 LM318 overheats

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bostoncruiser

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Recently tuned up my 1977 Luhrs single Chrysler 318 LH rotation vdrive and after running it up to 3000 rpm split a hose on the port intake manifold.

Pulled old hose and put on new one and the motor runs hot...shut down and pulled that hose that I just replaced and fired it back up and water flows good through that hose. pulled last hose right before exhaust and it seems to flow ok.

the system is just pumping hot water no cooling...and I can't figure out where the thermostat housing is???

Raw water intake has no strainer...into a sherwood pump....then over to a heat exchanger hanging on the starboard side...there is an overflow tank at the top of the motor centered on the stern side next to the carb

I learned from this forum that I have to bleed the air out when I pull a hose like that, so I guess that when I removed the last fitting before one of the exhaust that would bleed out the air as I ran it??

If the cooling system is moving water ok throughout then it must be in the heat exchanger or the thermostat is not opening??

any help would be great the season is so short here in MA.

thanks
Captn Steve
 
Thermostat is indeed underneath overflow tank
Coolant is flowing into overlow tank with cap off
hoses are cool coming into heat exchanger
hot coming out still running too hot??
 
I pulled the heat exchanger and took it to Holt in Saugus MA to get it checked out...looks clean Zinc was broken off and floating around inside.

Next place to look is transmission cooler since I do not have a raw water strainer might be blocked there
 
You could also try disconnecting the cooling hoses starting at the heat exchanger and flushing out with a hose in the reverse way water would normally flow. you could have broken impeller pieces or grass in there. then do the same for the other hoses and trans cooler, hoses to the risers and manifolds etc. Also if you have a walter vee, there's a rectangle cover plate on top of the unit where cooling raw water flows take it off and clean any gunk out, it gets clogged in there, hope this helps
 
Help !
I bolted up the heat exchanger that checked out fine from Holt in Saugus MA
checked out the transmission oil cooler no blockage there.
filled it up with 50/50 and started it up and same thing happens.

pumps cool in all the right places for a while and then starts heating up from the exhaust manifolds and then creeps backwards.

the tstat opens and fluid is circulating in overflow tank with cap off.

I would guess that I need to check the exhaust manifold logs to look for a blockage ???

I have LM318 short block with exhaust manifold logs on each side water comes into the back, how do I remove and check these. and then what.. move to the risers I have never done it for motors like this.
and of course the boat is on a mooring also.

summers flying by.
thanks to all Capt. Steve
 
Try a couple of easier items before tackling the manifold. Replace the impellor and try it. If that doesn't solve the problem, replace the T-stat.
 
Have rebuilt many and worked on LM318's most of my life. Had a 32' luhrs with twin 318's (v drives) and now have a 31' Egg Harbor with same (straight drive). Try running the motor without the thermostat and see if it still heats up. I agree that you may want to check the impeller. An easy way to do is to take off just the belt and if possible a single hose off the sherwood RW Pump and use a flashlight to look in the hose fitting and turn the pump by hand to check if all tabs are still on the impeller. this is a quick check method, but, an impeller can also just get worn and soft. A new impeller will most always give you quite a few degrees less temp. I don't know where you live, but, if eel grass is in your area not having strainers will most likely clog your oil cooler. If you don't know hte last time you changed your impeller DO IT!! and keep a log of all your maintenance. you can check your stat on the stove in boiling water with a thermometer to see if it's working at the correct temp, however, they are so cheap if you have it out just replace it. Since your running a fresh water motor you can use a regular automotive stat. fresh water stat should be around 170-180 degrees salt water motor should be brass or stainlees marine stat at around 140 degees tops. If you need help on the manifold job contact me. Many tricks can be done without removing the manifolds. You will want to get all the gaskets before this is performed.

Good luck!!
 
Thanks for the help WoodieMan & dlcarrvdot,

I did take a look at the impeller when I had the upper hose off the Sherwood raw water pump and it had tabs on it, I didn't rotate it, I can try that next.
I did pull the overflow tank off and look at the tstat it looked open to me, but I can try it without it in there.
I did look at the oil cooler and it looked clean, no grass or jellyfish in there I am in salt water.

Since everything was working fine and then boom I split a hose, I am thinking that it is a blockage in the manifold or riser. I can tackle it next week sometime.
I'll send you a message dlcarrvdot thanks !
 
Is it possible that I have air in the system, making it so that water does not move through the manifolds?

how do you remove and check the manifolds & risers while in the water??
I have never done it
 
Hook your fresh water tank up to each side of the manifolds

Compare the flow

Better to take off the elbow

Dont know what you got different setups

If you have the 20 gegree elbow take those off and inspect the log manifold have an extra gasket for assembly.if the bolts are to rusted and you can get them loose its

Dont bother unless your ready to do the whole side or both sides with new ones

Pictures are nice to see what you got
 
Here's a photo of my single LM318 FWC

hose going into the manifold on the right opened up
I replaced it and it has been overheating ever since.
 

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i believe it is a single impellor pump
if it is building up pressure and expanding those hoses going into the manifolds
then it must be a blockage somewhere after that right?
 
As of today I learned that whenever you can see rust on the exterior of the surface that bad the inside is seriously worse I say the log to riser is clogged and that elbow is done

I just took the elbow of the log and it was half what you got there on the right looking at the pic
 
Acctually your elbow looks decent but the log is older and all that rust is going into the riser and other elbow make sure you clean those out if you reuse them
 
you could take the manifolds and risers to a radiator shop and have them boiled out, but be careful, if the things are over 6 or 7 yrs old, the manifolds could be in danger of rotting out. If they do, seawater will be sucked into the cylinders at shutdown, causing big problems. Also, do you get steam out of the exhaust? if so, then you got clogged manifolds or risers, Went thru the same thing 2 yrs ago, replaced both sides and problem gone.
 
I did get steam coming out yes...That's my next step I think pull both sides off if I can and take them to my friends at Holt in Saugus MA they are very helpful. Get them to check them out for me.
Much thanks to all on this forum for the help.
Isn't boating fun :)
 
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