Help!!! Merc Overheating Question

[tonka_shores]

I've checked past posts but still have a question. The boat: 1972 Ford 302 & 888 Merc sterndrive. A bit of history: I purchased the boat late last season. It went directly to a reputable mechanic to replace the impeller. When back on the water, it had a tendency to overheat at low RPM, but was OK at WOT. This season, it seemed to get worse every time out. Now, we can't make it across the bay without overheating. I've replaced the thermostat. I've pulled the hose from the lower unit with the motor running and I get lots of water flow. I've blown into the manifold hoses and there seems to be no restrictions there. My last option seems to be the water pump on the engine. But there's no squeal or leakage from the pump. Could this be the problem? Is there a troubleshooting procedure I could follow? I'll soon be bald from pulling my hair.

 

[dodge1971340]

Re: Help!!! Merc Overheating Question

Hi! before you bought The boat was the boat ever ran in salt water? because i got my boat from salt water and the water curclation pump (water pump) was shot on the inside all ate away and it is a 1992 302 and if your pump is a 1972 who nose how old it could be. if you changed the impeller and it is still overheating and you changed thermostat eather its your block water passages are ploged or your waterpump is shot, i would start there, when you have the waterpump off were the water gose threw the block look at it to see if there is any restiction. at low idel overheat sound like waterpump to me but boats have mine of there own LOL. and they will make you pull your hair out! Im getting my block back from the machine shop this week so we can start pulling my hair out. but love boatn and wrenchen. I hope that works for you. God bless Gary

 

[tonka_shores]

Re: Help!!! Merc Overheating Question

The boat's never been in salt water. It spent all of it's life on the St.Croix River (Minnesota) and the upper Mississippi River. I thought that the dirty water from the Mississippi might have built up in the manifolds, but as I mentioned, I blew through the manfold hoses and they seem free of restriction. I love the boatn, but you can have the wrenchin. My lovely wife and I just spent a romantic evening cruise tonight dinking around with an overheated motor. And I ain't talking about the her's . . .

 

[Haut Medoc]

Re: Help!!! Merc Overheating Question

Is it raw water cooled or a closed system?....<br />I will assume raw because you are in MN.<br />Blowing into the hoses, (I gotta laugh at the visual ) a'int really gonna tell ya nuthin' unless it is totally clogged .....<br />If you are convinced that you have enough flow from the transom......<br />I would look at the water dumps in the risers for partial clogs due to scale....<br />Just how old are the risers & mans anyway, they may be due for replacement....<br />At least the risers are easy to get at, so check them first....<br />I seriously doubt that the engine circulating pump is bad ....<br />I can't see the vanes rotting off in fresh water.....Check where I suggested first....<br />& post back ......JK

 

[tonka_shores]

Re: Help!!! Merc Overheating Question

I talked to the original owner and to his knowledge, the mans have never been rodded. I tried to pull the front plate on one of the manifolds but it wouldn't come off without excessive force. (So I didn't get it off. I didn't want to break anything.) When you say risers, do you mean the elbows? I can pull those off and look at them. What are the vanes you mention?

 

[Haut Medoc]

Re: Help!!! Merc Overheating Question

Yes, the risers are the 'elbows'....<br />If the manifolds & risers have never been off (or replaced) for that matter, you are way, way, way overdue for replacement....<br />Like I said, the 'elbows' are about the easiest thing to remove on that set-up......<br />You can remove them & check for scale where I said & see if it corrects your problem, but you are on borrowed time with risers & manifolds that old ......<br />When they fail, (and they will), you will get water intrusion into your engine & you will be looking at replacing that as well .....<br />Not trying to portray gloom & doom here, but old manifolds & risers failing is a fact of life....<br />Look in the 'search' function & punch in 'water intrusion' & you will see what I'm talking about ......JK

 

[tonka_shores]

Re: Help!!! Merc Overheating Question

Here's the latest. I pulled the risers off. At close inspection, they don't appear to be the same age as the manifolds--thicker paint and different pattern. There was some crud in there, like scale and small chunks. After flushing, water ran freely throughout. The manifolds are obviously not restricted. Water flows freely through there too. One thing I thought odd, although the mans and risers have matching holes at their connection point, the metal gasket does not have holes to let water pass through. There is a water line from the front of the engine to the riser itself, but is water supposed to pass from the man to the riser? Is that the right gasket? According to the picture on mercruiserparts.com the gasket should have holes. Also, where is the flapper located?

 

[tonka_shores]

Re: Help!!! Merc Overheating Question

One other quick question. What are the plugs in the riser for, and how the heck do I get them out? I put a half inch driver to them, but the don't budge.

 

[tystick]

Re: Help!!! Merc Overheating Question

Did you or po have overheating symptoms before changing impeller?<br /><br />Is there any possibility that your reputable mechanic is not so reputable? Maybe used the wrong impeller or did not change housing?

 

[tonka_shores]

Re: Help!!! Merc Overheating Question

At the end a full day of working on that boat, I can report that the hose from the impeller gushes water at idle. Water flows freely through the manifolds and pumps out of the front end of each one. So I can conclude that the engine circulating pump and lower unit impeller are working. Right? When I had the risers off, water flowed freely through them and out the dumps. I have had all the hoses off and there are no restricitons, old impeller vanes, or other clogs. When the water heats, up the brand new thermostat opens all the way. The boat still idles to an overheat condition. The guage is entering the red and the manifolds are too hot to touch.<br /><br />What the heck else is there?

 

[dodge1971340]

Re: Help!!! Merc Overheating Question

not to ask as a stuped ?? if you are getting all this flow how old is your heat gage if it was me i would try that if you getting good flow. when you say you are running the boat it is with ears with garden hose not in a barrel of water because if its in a barrel it will overheat in a short time no fresh water. and also like JK and i said with stuff that old there has to be some scale were you can not see also water will flow it will find its way but with scale it will slow over time kinda like when you eat bacon every day for 35 years your gona get ploged up the presser gose up but you still have flow till one spot you cant see plogs up completly and you die your motor will do the same just ask me after $700.00 mach work on the block and crank and 400.00 for a rebuld kit because of rizer falure and water intrustion into the motor i would take the rizers mans and curclation pump and start all over new and you can do that new for under 1/2 of a new motor. just take one of the rizers and mans off completly take to a hot high presser washer and and spray down in the water jackets and you will see what we mean everything but the kitchen sink will come out. I hate to sound that way but falure will happen if you are over heating. Good luck to ya. and God bless GP

 

[ski_atomic]

Re: Help!!! Merc Overheating Question

do you get water to the thermostat housing,and do you run it in the lake/river or from the bucket.

 

[dodge1971340]

Re: Help!!! Merc Overheating Question

Hey tonka any luck?? ??? just wandering.... Thanks and god bless!! Dodge