Mercruiser 470 overheating - tried everything

[thedockboy]

Mercruiser 470 -4 cylinder 170 HP, serial #5416868 keeps overheating. Replaced hoses, thermostat, water pump/impeller and keeps overheating. Water wasn't flowing so recently removed lower unit to replace waterpump/impeller - old impeller was good but casing on water pump seemed a little melted on the outside as did the sleeve connecting to water inflow pipe. While unit was off connected a hose to the inflow pipe on upper unit and ran the hose without starting engine. Hose circulated water all the way through the unit back out the crack in exhaust bellows. Removed drain plug by exahust manifold and water shot trough as well. After replacing the water pump/impeller etc. and re-instllaing lower unit, started engine with lower unit in large drum of water and water began to flow through systemthought I had it fixed - Shortly afterwards water stopped flowing and engine got hot. I am at a loss as to what it could be - any ideas?

 

[boatdiver2011]

Re: Mercruiser 470 overheating - tried everything

First thing that comes to mind for me is the size of the heat exchanger. 3" will overheat, 4" is just right. 2nd thing- these motors run antifreeze through them, and have a water pump on the engine it's self as well to circulate the anti freeze. It is possible that it is giving you trouble. that heat exchanger can have all the water in the lake, but if the anti freexe isn't carrying the heat out of the motor it does little good.

 

[badkins50]

Re: Mercruiser 470 overheating - tried everything

pull and check the thermostat, open up the heat exchanger and make sure its not plugged, check compression, make sure nothing worked through system and got stuck in the exhaust somewhere. Double check all gaskets, o-rings and installation of impellor. Make sure it was the right kit. If the casing and tube was melted then it got really hot, check all the oils for anything funny looking.

Keep looking and I'm sure some of the mercruiser master mind will be able to help shine some light on it for you. Alot of great people with tons of knowledge on iboats. Good luck.

 

[Don S]

Re: Mercruiser 470 overheating - tried everything

The outside melting on the outside of the pump in the drive would indicate lack of water in the exhaust. Might want to check your exhaust elbow and see if the passages are blocked and preventing water flow.

 

[thedockboy]

Re: Mercruiser 470 overheating - tried everything

Don S. - pulled off exhaust elbow and manifold. It seems previous owner replaced the gasket between the elbow and manifold with a "solid" gasket - one without the openings cut in for the holes to allow antifreeze to flow up into the elbow. I do not know if this is the definitive problem but I would assume that is not good. Could this be THE cause of the lack of waterflow and overheating?

 

[dingdongs]

Re: Mercruiser 470 overheating - tried everything

yes.fit the correct one.if you want to test today and dont have one and the gasket is not destroyed ,cut holes with a scalpel /knife and then test.

 

[lime4x4]

Re: Mercruiser 470 overheating - tried everything

On my 470 my riser gaskets are solid. No slots. My exhaust manifold has antifreeze in it. The riser gets fed from the coolant exchange from a hose which contains lake water. I think if u cut slots into your gaskets you'll be adding antifreeze to the exhaust water which would then create a over heat

 

[Desertsky]

Re: Mercruiser 470 overheating - tried everything

Mine actually has a stainless baffle to prevent coolant from entering the elbow. If you open those holes, you will lose all your coolant. Raw water from the heat exchanger goes into the elbow and out the exhaust cooling the pump housing. If the pump quits, or youhave a leak elsewhere, the pump housing will quickly deform or melt.

 

[stonyloam]

Re: Mercruiser 470 overheating - tried everything

started engine with lower unit in large drum of water and water began to flow through systemthought I had it fixed - Shortly afterwards water stopped flowing and engine got hot. I am at a loss as to what it could be - any ideas?

That could be your problem. As I understand it, the water level must be above the impeller pump for it to pump properly. Just having the water cover the inlets will not do it. If the water level drops below the pump it would stop pumping. Much better to use a hose and muffs to get a positive water flow.

 

[stonyloam]

Re: Mercruiser 470 overheating - tried everything

"pulled off exhaust elbow and manifold. It seems previous owner replaced the gasket between the elbow and manifold with a "solid" gasket - one without the openings cut in for the holes to allow antifreeze to flow up into the elbow"

That is correct.

For your sn you should have a plate like this: http://www.mercruiserparts.com/showSpecialPicture.asp?pn=55730 and here are how the gaskets stack: http://www.mercruiserparts.com/Show...+MANIFOLD+ASSEMBLY+AND+EXHAUST+ELBOW+ASSEMBLY

Seawater exiting the heat exchanger cools the riser, not antifreeze.

 

[45Auto]

Re: Mercruiser 470 overheating - tried everything

As I understand it, the water level must be above the impeller pump for it to pump properly.

Have you ever noticed where your outdrive is when your boat is properly on plane? The anti-ventilation plate should be on the top of the water, and your waterpump is above that ....

You can see the waterpump housing sticking up well above the anti-ventilation plate (level with the boards) in this pic:

 

[stonyloam]

Re: Mercruiser 470 overheating - tried everything

Have you ever noticed where your outdrive is when your boat is properly on plane? The anti-ventilation plate should be on the top of the water, and your waterpump is above that ....

True, but you are also forcing water into the inlets when you are at speed. I do not believe that the impeller is very good at sucking water up in a static situation.

 

[jeepee]

Re: Mercruiser 470 overheating - tried everything

I have the same problem and I'm thinking that it could be the timing. After checking the timing, I will connect the left engine's water hose to the right engine and connect the right to left and see if the same engine still overheats.

 

[d55olds]

Re: Mercruiser 470 overheating - tried everything

I know this is an old thread. I was googling around and came across this topic. You riser is most likely clogged. I have dealt with many of this problem on Merc 470. I own a pair of them myself and love them. Do not and I repeat do not replace with aftermarket. Spend the extra hundred bucks and buy a new Mercruiser only Riser and gasket. This will correct the problem as long as your raw water impeller and cooling path is good. Cheers and good luck.

 

[Bob_VT]

Re: Mercruiser 470 overheating - tried everything

Announcement: -------------Please DO NOT reply to old threads or hijack existing threads. Old threads of a technical nature are like a library book, Do Not write in them.Don S

[FONT=arial, sans-serif]‎(Moderator)[/FONT]

[FONT=arial, sans-serif]and our forum Rules and guidelines[/FONT]
12. Please do not post to threads that have been inactive for more than 3 months UN-LESS you are the original poster. This is a very active forum and any thread that remains inactive for that long should be considered "dead". It is especially confusing when there is an entirely new question posted to an old thread. This is considered a hijack. Please start a new thread of your own.

Welcome to iboats. Trust me...... we get many occasions to answer 470 questions

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