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318 heating Gremlin

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rayb

Member
"Hi all, whilst you gentlemen

"Hi all, whilst you gentlemen are getting ready for winterization, ( whatever that is) we in OZ are just about to start our summer, although we have been boating all winter, this is when it gets really enjoyable. After saying that you may not want to help me with my little problem.

I have a LM318 1980ish, with half closed fresh water cooling.

It has started throwing a new trick at me after running flawlessly for the last year or so.

The symptoms are, start up OK, idle up to a reasonable temperature about 150F, ( 160F thermostat) and head out to sea. Run up to cruise about 2800 RPM and temp goes right up to just under 200F. I pull the throttle back to 2000RPM and she immediately cools back to about 170F.

Throttle back up to 2800 and the same thing, straight back up to 200F. On this second time back to 2000RPM, down comes the temp back to 170F, and after that never moves off the 170F mark for the rest of the day at any RPMs, 3500, 2000, or at idle, stops and starts perfectly when hot, no other problems.

It seems that it is not a raw water pump issue,
and I have recently put in a new thermostat, after testing it first in a container of hot water.

I am beginning to think it may be an air pocket somewhere that clears after a run, and then re appears somehow before the next use. New heat exchanger less than 25 hours use.

Am i missing something basic, has anyone else experienced a similar symptom, any comments will be sincerely appreciated, thanks in advance for any assistance.

Ray"
 
"Sounds like either your raw w

"Sounds like either your raw water impeller is getting ready to give up the ghost, or perhaps you have a riser or manifold that needs to be cleaned out. If you suspect an air pocket somewhere, you could find that quite easily using a surface temp gun."
 
"Hi Andy, thanks for your repl

"Hi Andy, thanks for your reply.

New manifolds and risers 2 months ago, so probably not that.

I thought of the impeller, but sort of discarded that idea because it pumps ok at all revs after we have the initial episode each day. I will revisit that now that you have mentioned it.

I have an infra red temp gun on the boat and will take your advice and run it over the motor.

I seem to remember on a previous occasion a couple of years ago after the boat had been slipped for anti fouling, that on start up the temp went right up to well over 220F and the mechanic started squeezing and working a hose down near the heat exchanger saying it had air in it, and after that the temp was normal.

I had better investigate that possibility as well.

Thank you for your inerest and time taken to reply.

Ray."
 
"G-day! I'll bet you a pi

"G-day! I'll bet you a pint o' bitters you have an air leak before the raw water pump. The TINIEST air leak raises holy hell with cooling, as I discovered this summer; the gasket on the strainer was leaking. Did exactly what you're describing.

Jeff"
 
"Hi Jeff,

I had the boat sl

"Hi Jeff,

I had the boat slipped and then re launched just prior to this happening. Does that mean that the air that obviously filled the raw water intake was then pushed up into the strainer and from there into the pump etc from the pressure of the sea coming up under the boat on re launch.

Would that do it ? and if so how would I "Bleed " it out, or will it work it's way out over time ?

Thanks for your comments, and interest."
 
"Jeff ,here in QLD have a 0.05

"Jeff ,here in QLD have a 0.05 level land or sea. I enjoy a can of XXXX GOLD. Summer activity. The procedure is to remove a can from the refrigerator and place into the freezer, for 10 minutes. When this operating time and hence temperature has been reached, the can and a beer glass are removed. Upon opening and pouring there should be mild ice flows forming on the surface in the glass. [ My beer glass lives in the freezer.] On all models of the Australian Beer Can a pressurized leak does develop when the ring pull is activates. This is a design feature!. I have been told that this manufactured product has a use by date. My participation would make a bar owner go broke. I am unsure what the conversion factor is for minuter. As for our climate in Brisbane. Google Earth. Frederick Pel"
 
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