Mercruiser 470 Oil & Water mix in engine

[Mattb22006]

I'm buying a 20' boat with a Mercruiser 470 engine (and yes I've read all about them). But the owner has stated he had it running last season until the motor starting mixing oil and water. I'm looking to the experts to help me understand the possible causes for this. Not to tell me not to buy it please.

It has already had the alternator conversion. I am planning on doing the heat exchanger upgrade myself after purchase.

 

[wahlejim]

Most likely causes in a new to you boat:

1) Improper winterization resulting in a cracked block. Remedy: replace engine

2) Overheating causing major problems, including failed exhaust system gaskets, melted shutters, failed engine gaskets.

 

[Mattb22006]

I doubt it was improperly winterized since they used it for a whole season and then experienced the water/oil mixture. Since it still runs, I'm leaning more towards failed gaskets. I will likely tear down the motor and replace all the gaskets anyway.

 

[GA_Boater]

Welcome aboard.

Since we won't try to talk you out of buying :smile:, and 470's should have antifreeze in the closed cooling system which should preclude freezing and cracking the block, the most likely fault is a blown head gasket. 470's blow head gaskets because the aluminum block and cast iron head expand at different rates. Do a compression test before tearing it apart.

 

[Maclin]

These can leak at the cam bearing seals and coolant mix can get into the crankcase that way, common problem with these engines. There are some remedies for this involving speedisleeves I believe.

 

[GA_Boater]

These can leak at the cam bearing seals and coolant mix can get into the crankcase that way, common problem with these engines. There are some remedies for this involving speedisleeves I believe.

Yep - Forgot this one on the "most likely" list.

 

[Mattb22006]

Thanks guys, thats what my research has precluded as well. Going to give her a compression test and see what happens. After all $600 for a 20' boat, motor and trailer is quite a steal.

 

[Mattb22006]

Welcome aboard.

Since we won't try to talk you out of buying :smile:, and 470's should have antifreeze in the closed cooling system which should preclude freezing and cracking the block, the most likely fault is a blown head gasket. 470's blow head gaskets because the aluminum block and cast iron head expand at different rates. Do a compression test before tearing it apart.

Just for my own curiousity, how does a blown head gasket cause water to seep into the oil? Wouldnt it be antifreeze?

 

[stonyloam]

Yeah, first question, is it water or antifreeze? You should be able to smell antifreeze in the oil. If it is antifreeze check the weep hole in the engine water pump. Is it open? If it is plugged coolant will leak past the first of two seals, and then past the second seal into the engine. The weep hole is designed to let coolant leak out rather than past the second seal. Sometimes folks will see the antifreeze leaking out and plug the hole. Bad head gasket will let coolant into the oil. If it is water, the only place it could get into the oil is at the exhaust elbow. If you have a 3" exchanger and it is in good shape, IF you keep the outdrive impeller in good shape ( change every other year) it should work fine, already has for 30 years.

 

[GA_Boater]

Just for my own curiousity, how does a blown head gasket cause water to seep into the oil? Wouldnt it be antifreeze?

Because it is an AF/water mix, not pure antifreeze. Milk shake oil won't look any different whether it's straight water or a mix.

 

[stonyloam]

Because it is an AF/water mix, not pure antifreeze. Milk shake oil won't look any different whether it's straight water or a mix.

That is correct, but you should be able to detect the distinct odor of antifreeze in the oil.

 

[Scott Danforth]

Thanks guys, thats what my research has precluded as well. Going to give her a compression test and see what happens. After all $600 for a 20' boat, motor and trailer is quite a steal.

the cheap and free boats are the most expensive to own.

at least you got it cheap enough you can go get a 4.3 to replace the 470.

have you priced the larger heat exchanger, and the updated manifold/elbow yet. you may want to look into the costs.

 

[Mattb22006]

the cheap and free boats are the most expensive to own.

at least you got it cheap enough you can go get a 4.3 to replace the 470.

have you priced the larger heat exchanger, and the updated manifold/elbow yet. you may want to look into the costs.

Yeah, I've looked at all options really. Any idea how much a used 4.3 would run me ball park? Assuming all the labor was done by myself.

 

[Mattb22006]

Also, just wanted to say thanks guys. Your community has been extremely helpful. I'll keep updated if I buy this boat, going to look at it tomorrow. Looking forward to your valuable assistance in the future.

 

[Maclin]

Here is something I posted a long time ago to a 470-curious member that you may find relevant...

Maybe you know of these, but here are some typical upgrades and things to watch for with the 470, all of this is from posts here in iBoats..

External alternator upgrade.
The 470 uses the same type of charging as an outboard with magnets and stator, with a water cooled voltage regulator. I am probably not getting it quite right, but a very common upgrade is to install an actual pulley driven alternator internally regulated. You need to dig in a bit and scrape the magnets off the back of the balancer, as even though they are no longer used (after this upgrade) they can come loose and sometime even bind up to where the engine won't turn.

4 inch heat exchanger.
Yours may already have this, but if it is just the 3 inch then changing it out for the 4 inch is a very good idea and worth the effort. A common demise of the 470 is an overheat, and the head can warp, lots of things go wrong as fallout from the event cascades. With the aluminum head and iron block, and the head floating with no dowels or other locating help this is one thing (bad overheat) that can cause high dollar fix due to hard to find parts.

Cam bearing seal leaks, another very common epitaph on a 470's tombstone.
The front cam bearing sealing components almost always eventually fail I guess. There is a speedy-sleeve fix, all I have about this is from reading some very sad posts here. If caught in time while it is just weeping, the speedy sleeve fix can save it. Just depends on how long the engine has been run as water is entering the oil pan the whole time.

I may be leaving some small items out, and of course your mileage may vary. Another common upgrade is electronic ignition, again searching here can produce some success stories in each of these areas. Some guys here run these very successfully. While you need to be mechanical, when you stay ahead of them you get a lot of power and reliability out of them.


Good luck with you project!

 

[Scott Danforth]

Yeah, I've looked at all options really. Any idea how much a used 4.3 would run me ball park? Assuming all the labor was done by myself.

You can find running 4.3's all day long in junk boats for about $1500. scrap the boat, sell the trailer and sell off your 470 stuff and you could come out money ahead

 

[stonyloam]

A 3" heat exchanger is perfectly adiquate IF you do the proper routine maintenance, keep it clean and change the impeller every other year. The 4" gives an extra margin of safety if you get reduced flow from a neglected impeller. I would suggest, if you keep it, replace the whole impeller and housing with a new OEM unit, and you should be good.

 

[QBhoy]

Is the FW internal cooling header tank loosing water ?
That would tell you if it's internal cooling issue like cylinder head or mechanical engine driven water pump seal (although I think there is a tell tale for this if it's leaking outwardly)
If not, can't quite remember, but is there an oil cooler that is SW or external/raw water cooled that has an interface seal leaking ? Been a while since I've been around this engine....since my friend got rid of it.
As some have said...if it looks serious...don't persist and invest too much.
A 3.0 or 4.3 can be picked up really cheap. The 4.3 needs fibreglass work for new engine mounts...the 3.0 goes straight in. Depending on the boat and weight...may need to think about different gear ratios or props, if so.

 

[2fishy4u]

I started the same way. I bought a 12k boat for 3k. Because one of the 470's "was not running" turned out number 4 had a big hole from a overheat. So, I figured no biggie. I had it completely rebuilt. It ran awesome for 50 hours. Then a piston rod broke..... Problem with rebuilds is there are still 25 year old parts being used. So, I bought a reman. At least I had a warranty. Its been running fairly well for 130 hours. Then the other engine starts knocking...... Uggh..... So, another reman is bought. 120 hours later. Within a 5 minute span of not looking at the temp gauge. Blown head gasket....... $40k later I wish I would have listened to all the people saying run from this thing. Still trying to fix a NEW heat issue before I can finally sell it and buy something reliable......I got a boat worth 8k if I can get it to stop overheating...... And it only cost me 40k to get it there. I hope to some day get everything running right so I can finally get rid of it.

 

[stonyloam]

If you decide to go with a "conventional" Mercruiser, forget the 3.0, in a 20' boat it would be a dog, and the outdrive gear ratio would be wrong. A 4.3 uses the same outdrive gear ratio as the 470 but is about 200 pounds heavier. Couple of things with the 470: if you have the alternator conversion, you do not remove the magnets, because the rotor is balanced with them in there, you remove the stator, so if a magnet does come loose it will not jam up. If your weep hole is leaking antifreeze, chances are it is not going into the crankcase because there is a second seal in there to keep it out, as long as the weep hole is not plugged.