Over heating on inboard Mercruiser (HELP)

[theresajo1]

I am writting this for my dad since he is computer scared! anyway his boat runs good at 30 mph temp. at 140 to 150 but when he hammers it down like he says it climbs over 200 and then he cruises again at around 30 mph it slowly goes back down? We ahve a book on how to take it apart but not what is wrong with it?? new water pump in stern drive, and that all redone. is it the exhaust elbow? we took that off and it looks fine but ther is no gaskets there anymoe? could that cause the problem or the Exhaust manifold? there is a little water the drips from underneath there? if that is the problem is it or any of it hard to change? or fix.... also by changing plugs help it start better? Any help would be greatly appreciated! Thanks so Much!

 

[Skipster1]

Re: Over heating on inboard Mercruiser (HELP)

We need more specifics.<br />What engine is it and what year?<br />How many people on board when he "hammers it down"?<br />What RPM is "hammer it down"?<br />What kind of boat and how big?<br />When was the last time the impeller was changed?<br />What other changes have been made recently?

 

[theresajo1]

Re: Over heating on inboard Mercruiser (HELP)

ok this is what i got from my dad<br />Engine 140 hp 4 cyl, mercruiser inboard...... 1976 for year <br />we had 3 people on board <br />RPM's dad said he never looked for got about that part<br />boat it is a glass master at length of 16 feet capsity of 6<br />I don't know what the impeller is? or were it is located? so no has not been changed<br />new oil new oil filter, all the whole stern drive redone what else will help let me know?

 

[theresajo1]

Re: Over heating on inboard Mercruiser (HELP)

forgot Alpha one

 

[theresajo1]

Re: Over heating on inboard Mercruiser (HELP)

anyone?

 

[fripsy]

Re: Over heating on inboard Mercruiser (HELP)

I don't know that Mercury engine, but the impeller is that thingy inside the rawwaterpump, it pumps seawater to cool through the heat-exchanger the closed water circuit of the engine.<br />If that impeller is worn out or cracked, it pumps not enough water to cool the engine.<br />Also chack the filter on the rawwater circuit.<br /><br />Frank

 

[fripsy]

Re: Over heating on inboard Mercruiser (HELP)

ChEck the filter... that is...

 

[fripsy]

Re: Over heating on inboard Mercruiser (HELP)

look at this thread, there is a drawing of an impeller:<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=007753

 

[Skipster1]

Re: Over heating on inboard Mercruiser (HELP)

Need to know also what themrmostat you are using. If it is a 140 I would guess that, given the conditions you describe, this is not a big deal. Especially if you have the hammer down for a long period of time and three people.<br />Basic thumb rule: Keep it under 4000 rpm unless you have to go higher. When running above 4000 - for sustained periods of time - you will wear out parts such as oil pump, fuel pump, etc.... and engine will wear out much faster.<br />So go ahead and take her out and run her at 3500 for a couple of minutes and watch the Temp gauge .... does it rise right away? If it does then come on back here and let us know.<br />If the temp just slowly rises and then holds at 200 degrees - with a heavy load - it's probably okay. <br />And then come on back an let us know.

 

[theresajo1]

Re: Over heating on inboard Mercruiser (HELP)

Ok now I know what the impeller looks like so that is in the stern drive right? if that is the case that is brand new.... This is fresh water also. <br /><br />As for the temp I can tell you thatit stayed at a constant 145 150 as long as it stayed around 30 mph..... but then when we would go around 50 which it was plenty fast for me it shot to 200 and above but when we went back around 30 again it slowly went down to 180 then 150 but took a while then we would run it again! Dad was thinking of replacing the thermostat? Also on the elbow the Gaskets are non exsistent.. so have to get soemthing for that? can you jimmy one up from something like NAPA close to it? Dad's Idea? Also there is a little water leak from under the Exhaust manifold? i mean nothing major but a little one? anything to do over heating? and do all those imboard boat hard to start? and changing spark plugs will that help to improve it's start? thanks so much great help to my dad! and well to me to since I have to help him.

 

[HULKSTERUPS]

Re: Over heating on inboard Mercruiser (HELP)

50mph Thats fast for a 140.

 

[theresajo1]

Re: Over heating on inboard Mercruiser (HELP)

would that help if to put in a higher thermostat in?

 

[Skipster1]

Re: Over heating on inboard Mercruiser (HELP)

You have to be more specific. Did you run it up to 50mph or 5000RPM?<br />If 5000RPMs you're over-revving and causing over-heating.<br />What thermostat do you have in? (I asked this once already). Don't change anything yet .... all in all, it sounds like the engine is running fine.... you're just pushing it a bit too hard.

 

[theresajo1]

Re: Over heating on inboard Mercruiser (HELP)

It is a 140 thermostat in it, RPM's Dad was not sure what it was running it? but he wanted to know how fast do you need to go for it to pull a skier? I know 50 is way to fast and to hard for boat for an older boat also... we will take it out sunday and check it all over again. Thanks a bunch you don't know how much that helped out!

 

[theresajo1]

Re: Over heating on inboard Mercruiser (HELP)

I just wanted to update you after I took that boat out....... We took it out sunday after changing the plugs, adn changing the elbow gasket and we had 4 people in the boat, and extra water in it since people don't know how to put the plug in boat... ( not me ) but anyway we ran around 40 to 50 mph adn the boat temp ran about oh 160- 180 adn went down when the mph went down? I think that temp is alright? But thanks for all your help out there... wishI could help out others but not smart enough on boats yet. Thanks again! Theresajo

 

[Regal27]

Merccruiser Alpha one 350- 265 HP Overheat

Merccruiser Alpha one 350- 265 HP Overheat

Hello All,
I really need your help. I seem to have tried everything.

Have a two year old rebuild 350 with raw water cooling. No problems for one season and 3 months. One day lst week- at about 3200 RPM for ten minutes - I burned up the RT side (starboard) rubber exhaust boots.

Rt Exhaust header had rust problems.
New headers installed both sides- still overheating.

No thermostat - new Impeller- Still overheating
Find Cracked exhaust manifold-replace -----Still Overheating

Rt side runs 40-50 degrees hotter that LT side using IR thermometer

Any ideas? Our Club mechanic is out of ideas.

Thanks for any help

 

[ESekelsky]

Re: Over heating on inboard Mercruiser (HELP)

I really think you should get the correct thermostat in the boat. Then test the flow from either the lower and if applicable upper hoses to your exhaust manifolds. Look at the thermostat housing does it have check valves. Test of they are stuck or remove and replace thermostat housing if you cannot get water to come out of the feeds to the manifolds. You can remove one exhaust cooling hose at a time and report back with your findings. That?s what I am currently working on with my boat. lookup ESekelsky posts. I have one manifold hotter than the other. Reduced flow from one cooling hose coming from TSTAT. I also suspect wrong gasket in exhaust. Boat has restrictor but literature states to use open or 4 port.
Also verify correct elbow and riser gaskets. 4 port or 4 hole or restrictor or closed. you need to have the correct exhaust gaskets in your exhaust system. Also BOTH sides must be correct and match.

 

[gadget73]

Re: Over heating on inboard Mercruiser (HELP)

If I had to guess, you've got old impeller bits somewhere clogging up the works.Try backflushing the water feed lines to see if any garbage comes out. Either that, or one of those check balls is stuck and you're not getting proper flow to the manifolds.