mercruiser 470 burning coolant (long)

bansheejoel

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I bought a boat with a 470 in it last year. Runs great but it has always lost a little coolant while sitting over night if i didnt relieve the rad. cap and release the pressure. It never smelled like coolant however today i took it out for the first time this season. It ran good on muffs the day before.

When i went to start it in the water it took forever to start, when it did it blew a decent cloud of white smoke and stunk like coolant. I fished all day and when powering up i could smell the coolant again, pretty much the whole time i was heading to shore (4miles). Got home, checked coolant level and it was low.

Pulled the plugs and 2, 3, and 4 were dark brown. Plug 1 was a little lighter but not much. Checked compression and it was a solid 150 psi on all cylinders. My engine has a newer aluminum exhaust manifold and heat exchanger. Any ideas? Only thing i can think of is maybe the riser gasket is leaking and its burning and going out the exhaust. Any help is appreciated! Thanks
 

alldodge

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Re: mercruiser 470 burning coolant (long)

I bought a boat with a 470 in it last year. Runs great but it has always lost a little coolant while sitting over night if i didnt relieve the rad. cap and release the pressure. It never smelled like coolant however today i took it out for the first time this season. It ran good on muffs the day before.

When i went to start it in the water it took forever to start, when it did it blew a decent cloud of white smoke and stunk like coolant. I fished all day and when powering up i could smell the coolant again, pretty much the whole time i was heading to shore (4miles). Got home, checked coolant level and it was low.

Pulled the plugs and 2, 3, and 4 were dark brown. Plug 1 was a little lighter but not much. Checked compression and it was a solid 150 psi on all cylinders. My engine has a newer aluminum exhaust manifold and heat exchanger. Any ideas? Only thing i can think of is maybe the riser gasket is leaking and its burning and going out the exhaust. Any help is appreciated! Thanks

I would suggest pulling the exhaust and have a look, you have a leak
 

achris

More fish than mountain goat
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Re: mercruiser 470 burning coolant (long)

Pressurise the cooling system and see if you can locate the leak...
 

stonyloam

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Re: mercruiser 470 burning coolant (long)

If you were leaking that much into a cylinder seems like you would have steam cleaned the plug insulator snow white (like mine did). Agree with the other guys, look to the exhaust elbow gaskers first. Good luck.
 

VeroWing

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Re: mercruiser 470 burning coolant (long)

How does your oil look? I recall having a 470 that had a leaky seal between the water pump and inside of motor. Water pump is on end of camshaft and seal is behind impeller separating water from oil. Sometimes a groove is worn into the camshaft from hardened seal and starts to leak water into crankcase. There is a kit available to press a sleeve over this area on cam and then a new seal to correct problem.
 

bansheejoel

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Re: mercruiser 470 burning coolant (long)

Oil looks perfect. Put 11 hours on it trolling saturday. Im going to try and pressurize the cooling system today. Hope i can find something. Did notice last night the exhaust manifold bolts were very very loose. Im not sure if that would have anything to do with it?
 

stonyloam

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Re: mercruiser 470 burning coolant (long)

Well coolant flows through the manifold to cool it so retotquing the bolts might be a good idea.
 

bansheejoel

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Re: mercruiser 470 burning coolant (long)

Well i broke down and spent the $85 for a pressure tester. Pumped it up to 15psi and let it sit. It deffinatly lost some pressure but not much. Maybe 1psi in 10 mins. I pulled the exhaust manifold and all the exhaust ports have alot of carbon on them and the tops of the pistons are dry. It DID however lose some coolant after being run yesterday on muffs then sitting all day today. I didnt see any signs of coolant in the manifold (upgraded aluminum not cast). I dont understand this damn thing.
 

alldodge

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Re: mercruiser 470 burning coolant (long)

Well i broke down and spent the $85 for a pressure tester. Pumped it up to 15psi and let it sit. It deffinatly lost some pressure but not much. Maybe 1psi in 10 mins. I pulled the exhaust manifold and all the exhaust ports have alot of carbon on them and the tops of the pistons are dry. It DID however lose some coolant after being run yesterday on muffs then sitting all day today. I didnt see any signs of coolant in the manifold (upgraded aluminum not cast). I dont understand this damn thing.

When the engine is running it's at 140 or better degrees. Heat expands things, I'll still suggest removing the manifolds and elbows, it's probably leaking in that area
 

bansheejoel

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Re: mercruiser 470 burning coolant (long)

I pulled the exhaust manifold. Im going to get some rubber caps and pressure test the manifold/riser tomarrow. Is it possable its leaking in the intake manifold? If it was doing that i would think the plugs would be steam cleaned and their not.....
 

alldodge

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Re: mercruiser 470 burning coolant (long)

I pulled the exhaust manifold. Im going to get some rubber caps and pressure test the manifold/riser tomarrow. Is it possable its leaking in the intake manifold? If it was doing that i would think the plugs would be steam cleaned and their not.....

I don't see that as a possibility because of the plugs as you mentioned. Also if it was the intake there would be running problems
 

bansheejoel

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Re: mercruiser 470 burning coolant (long)

The weep hole doesnt leak. I have a bill that came with the boat for $2700 which included new cam, rebuilt long block, new aluminum manifold, and heat exchanger, head was also rebuilt. Had a two year warranty but ofcourse the warranty expired 9 months ago. I ordered a oem riser and manifold gasket. I will let ya know if i find anything tomarrow. Thanks for the help guys i appreciate it!
 

jabfd

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Re: mercruiser 470 burning coolant (long)

The weep hole doesnt leak. I have a bill that came with the boat for $2700 which included new cam, rebuilt long block, new aluminum manifold, and heat exchanger, head was also rebuilt. Had a two year warranty but ofcourse the warranty expired 9 months ago. I ordered a oem riser and manifold gasket. I will let ya know if i find anything tomarrow. Thanks for the help guys i appreciate it!

I would put the pressure test up to 15 psi and run a paper clip into the weep hole
Last year I spent I lot of time on my manifold thinking it was my problem turns out it was my cams seal people have replaced them and still have leaks bottom line just run paper clip or wire in the weep hole make sure nothing is blocked up it should go in about 3 and half inches . Let us know how the pressure test goes on the manifold .good luck
 

bansheejoel

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Re: mercruiser 470 burning coolant (long)

Manifold didnt leak at all. I did however find a leak on the front engine cover. The leak is coming out around a bolt my alternator bracket is bolted to. It explains why i could smell coolant but i still dont understand why i got the puff of white smoke on the inital startup? I took a pic of the bolt that its leaking around but cant seem to find how to post it.....
 

stonyloam

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Re: mercruiser 470 burning coolant (long)

A little NAPA (Permatex) aviation sealant on the bolt threads might fix that. The white smoke might be a little oil from worn valve guides??
 

bansheejoel

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Re: mercruiser 470 burning coolant (long)

I always thought oil burned blue? According to the engine bill the engine/head should have around 120hrs as of now. Hard telling though, im going to pressure test again today afterwork hoping the thread sealant sealed it up. If it did i can rule out a head gasket and put a new gasket on the front cover and be done.
 
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