cooling question

[russman]

i have a 1976, 888, 302 ford, pre alpha merc leg<br /><br />i had a over heating problem late last year.<br /><br />a new lower unit was installed 3-05 with new impeller so i figured the impeller pump on the lower unit was ok and changed the thermostat out with a new one (140-160 degree?)on the main motor.<br /><br />tested the boat and temp still continued to creep up to allmost 190-200.<br />so last weekend i removed the new marine thermostat and tested it in hot water and it opened up with no problems.<br /><br />next i removed the lower unit and checked the impeller, it to look like new and had not spun out on the hub.<br />so now iam puzeled and start looking at the the complete cooling system and decided to remove the water pump.<br /><br />other then being pitted and rusty inside it apears to turn smoth and it doesent apear to have leaked water out of the hole by the main bearing.<br /><br />so my question is their a way to tell if it needs to be replaced?<br /><br />also i remove the hoses to one of the manifolds and gave it the old blow test(wife was busy) and there did not seem to be any blockage.<br /> <br />does any one have any other ideas to check out.<br /><br />Lost in Kansas<br /><br /><br />russman

 

[I/O WALDO]

Re: cooling question

Look at the hose from the bellhous to the transom hous and 1-see if the hose is good and 2-look at where it connects to the bellhous and see if the is a hole corroded tru the nipple.If it is,water will shoot out while on the muffs!These bellhousings do that alot if crusty!

 

[Haut Medoc]

Re: cooling question

I have that model, but with closed cooling.....<br />I am assuming that you have a raw water cooled system....<br />You can do what Waldo says...<br />In fact a visual check for any obvious leaks would be the first thing to do.....<br />Next, I would take off the hose that runs from the transom to the engine & see how much water flow you have with the engine running.....<br />You should be able to fill a 5 gallon bucket in a fairly short time.....<br />Keep in mind not to run the engine too long with out the water supply or you will fry the rubber exhaust "boots"....<br />If that checks out, I would look for a restriction in the ports on the exhaust risers...<br />They can fill up with scale & restrict water from exiting the engine......JK

 

[Don S]

Re: cooling question

I would also recheck that impeller. Even if it was new, there is no way of knowing if it's damaged without looking at it. All it would take is a plastic bag over the water intake for a few seconds to damage the impeller.

 

[Buttanic]

Re: cooling question

Did you replace the stainless steel liner in the pump housing when you changed impeller. I had a creeping temperature problem on a 75 pre alfa 233. I changed the impeller and it didn't help, changed the liner and problem solved.

 

[russman]

Re: cooling question

Thanks for all the tips guys<br /><br />I did inspect the impeller on the outdrive and it looked good. i also tried to turn it to see if maybe it was spun loose from its center but it was tight.<br />the new lower unit has only a bout 10 hrs on it.<br /><br />i will reassemble and do some more tests this weekend and will advise what i find.<br /><br /><br />P. S.<br /><br />Congrats to Don S for the recent upgrade to <br />" Vice Admiral "<br /><br />You are a great source of wisdom on Mercs and other models for this web site!<br /><br /><br />again thanks to all<br /><br /><br />russman

 

[Buttanic]

Re: cooling question

Be sure part number 31 the pump liner is in place<br /><br /> http://media.stemtostern.com/defaul...n.com/LSDATA/LSDATA_FULL/CRUISER\60700\11.GIF

 

[Bondo]

Re: cooling question

Next, I would take off the hose that runs from the transom to the engine & see how much water flow you have with the engine running.....<br />

Before you reinstall the lowerunit,......<br /><br />Back-Flush this waterline,..... There Could be some bits,+ pieces of Old long gone Impeller pieces lodged in this line.......

 

[russman]

Re: cooling question

An up date;<br /><br />i removed all the hoses for the cooling system and flushed them with the garden hose.<br /><br />re-assembled everything, hooked up the water hose and woke the beast up for the first time of the year. <br /><br />after watching the temp gauge for 5-10 mins the temp went up to 160-170 and then started to drop down to 150 ish. all was good.<br /><br />next<br /><br />I wanted to see the water flow comming from the lower unit to the water pump so i removed the hose and turned the motor on.<br />At idle 600-800 rpms there is not much water being pumped out, as the rpm was increased it did increase the flow as well.<br /><br />but still i thought there would be alot more water comming out, i know the water pump outlet is only 1/2" <br />and the hose going to the motor is 1, 1-1/4" there just does not seem to be alot of flow.<br /><br />is this normal?<br />iam suprised it is enough to keep a v8 cool during trolling.<br /><br />the tempature seems to be ok on the hose but i will wet test it this week. <br /><br />any thoughts?<br /><br />russman