New Member with Mercruiser 470 problems

K

keithnpa42

Recruit
Joined
Jul 26, 2009
Messages
4
I have been reading a lot of posts on here and it has been very helpful. Now I?m hoping to get to the bottom of my problems.

1986 mercruiser 470 3.7 170hp......

First time on the water, it ran great for about an hour. It then started to over heat and I had to shut it down. It got to about 200 to 225 degrees. I got towed in, but it started right back up. When I bought the boat I was told that the lower impeller had just been replaced.

I checked the upper circulating pump and it was in good shape. I back flushed the system including the heat exchanger and replaced the thermostat. I changed the oil and replaced the coolant. Engine ran great on land with ears on never braking 175 degrees.

I take the boat on the water and within a few minutes it starts to get hot, and then started to spit oil out of the dipstick. I lost all the oil. I got it back to the dock put more oil in and it would turn over but would not start.

I took it to my mechanic and he believes I got coolant in the oil probably due to the seals behind the circulating pump failing.

I am having him do a compression test, and I will be changing the seals

What else should I do, and/or be looking at? How the heck can I get this engine to just run and not continue to have problems? Any help would be greatly appreciated.

Thanks
 
X

xltier

Chief Petty Officer
Joined
May 20, 2004
Messages
636
Re: New Member with Mercruiser 470 problems

they are very problamatic,thats y merc dropped them.
 
45Auto

45Auto

Commander
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May 31, 2002
Messages
2,842
Re: New Member with Mercruiser 470 problems

When I bought the boat I was told that the lower impeller had just been replaced.
Click to expand...

Don't trust what anyone tells you when you're buying a used vehicle. Check the impellor before you do anything else.
 
S

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
Re: New Member with Mercruiser 470 problems

Most likely a blown/leaking head gasket. The compression test will tell. If you need to replace it use OEM Mercruiser gasket. Let us know how it turns out. Good luck.
 
CAPTKEV85

CAPTKEV85

Petty Officer 1st Class
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Mar 12, 2008
Messages
229
Re: New Member with Mercruiser 470 problems

sounds like head gasket
 
JustJason

JustJason

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Aug 27, 2007
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5,319
Re: New Member with Mercruiser 470 problems

Check the diameter of the heat exchanger. If you have the old 3 inch one you need to upgrade it to a 4 inch one.
 
K

keithnpa42

Recruit
Joined
Jul 26, 2009
Messages
4
Re: New Member with Mercruiser 470 problems

well I got the compression test back and everything was fine with that. So Its change the seals first. I will look at the lower unit next if this does not fix the problem.

Thank you for all the advice and I will follow up after this weekend.

It does have the 4inch heat exchanger, but does anyone know how much coolant you should put in it? should you be able to see the coolant in the resevoir tank on top of the intake?
 
Last edited:
S

stonyloam

Vice Admiral
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Mar 13, 2009
Messages
5,827
Re: New Member with Mercruiser 470 problems

What were your compression numbers? The blowing oil out of the crankcase is still a mystery.
 
K

keithnpa42

Recruit
Joined
Jul 26, 2009
Messages
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Re: New Member with Mercruiser 470 problems

I have now found out the problem. My coolant reservoir seal was bad and it was leaking coolant right into the engine. This in turn caused the oil to blow out. In addition I now have a knock in the engine. Per a qualified mechanic he believes that the coolant got into the engine and washed the bearings and that is where the knock is coming from. He then told me all the wonderful things that will/could go wrong even if I got that problem fixed. In other words this engine is a piece of s h i t and I should get rid of it as soon as possible. Any other advice out there? Does anyone want to buy a boat real cheap? Let me know.

Thank You
Keith
 
Showtime22

Showtime22

Petty Officer 2nd Class
Joined
Jun 1, 2009
Messages
133
Re: New Member with Mercruiser 470 problems

I just swapped out my blown 470 for a Merc 260. I bought a donor boat for 800 bucks with a good 350 and lifted it with a cherry picker I rented for 42 bucks a day. I then used the cherry picker to place the 470 block in the trash container. By swapping I gained an alternator system, power steering, and a motor that rips.

It's not a real hard swap but I do not recommend it unless the boat is at least an 8 out of 10. Mine is a 6. If you do decide to do a swap I will post a longer list of issues I dealt with in the swap.
 
K

keithnpa42

Recruit
Joined
Jul 26, 2009
Messages
4
Re: New Member with Mercruiser 470 problems

I am looking at a few options on an engine change out. Will a 165hp mercruiser straight 6 fit without any modifications to the boat? It is a front mount engine, but do you have to change the out drive? Is there any other issues that I should know about when changing it out?

Thanks,
Keith
 
B

boltonranger

Petty Officer 1st Class
Joined
May 2, 2004
Messages
204
Re: New Member with Mercruiser 470 problems

keithnpa42 said:
I have now found out the problem. My coolant reservoir seal was bad and it was leaking coolant right into the engine. This in turn caused the oil to blow out. In addition I now have a knock in the engine. Per a qualified mechanic he believes that the coolant got into the engine and washed the bearings and that is where the knock is coming from. He then told me all the wonderful things that will/could go wrong even if I got that problem fixed. In other words this engine is a piece of s h i t and I should get rid of it as soon as possible. Any other advice out there? Does anyone want to buy a boat real cheap? Let me know.

Thank You
Keith
Click to expand...

Keith that gasket can fail on different motors - it didn't fail because it was a 470.
What I mean is you could have had this happen with a different engine/boat.
The 470 is not a "bad" engine. Why not repair it?
Then you'll KNOW what you have instead of taking someone elses word.

How bad of a loss do you think you will take if you sell it?
-br
 
bigskiohio

bigskiohio

Master Chief Petty Officer
Joined
May 3, 2008
Messages
882
Re: New Member with Mercruiser 470 problems

what i have read the aluminum head is a problem with them and they problematic , my suggestion is dont buy one to find out if it is true or not.
 
B

boltonranger

Petty Officer 1st Class
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May 2, 2004
Messages
204
Re: New Member with Mercruiser 470 problems

bigskiohio said:
what i have read the aluminum head is a problem with them and they problematic , my suggestion is dont buy one to find out if it is true or not.
Click to expand...

Head is iron, not aluminum.
-br
 
Rocky_Road

Rocky_Road

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Oct 8, 2008
Messages
1,798
Re: New Member with Mercruiser 470 problems

boltonranger said:
Head is iron, not aluminum.
-br
Click to expand...

Agreed...the block is aluminum, and the head is iron. There are aluminum heads out there, but I have never heard of one being adapted to the marine engine.

Many people blame the head gasket problems on the differing metals used by Mercruiser....
 
W

whatsagm

Seaman
Joined
Feb 26, 2008
Messages
58
Re: New Member with Mercruiser 470 problems

Keep the 470, I have done all the up grades on mine. I love this engine. Good on gas and good power. I fixed the cam seal issues upgraded my charging system and heat exchanger.
 
T

The Begginer

Seaman
Joined
May 28, 2021
Messages
66
whatsagm said:
Re: New Member with Mercruiser 470 problems

Keep the 470, I have done all the up grades on mine. I love this engine. Good on gas and good power. I fixed the cam seal issues upgraded my charging system and heat exchanger.
Click to expand...
What uprgrades do you speccifucally have ??
 
Scott06

Scott06

Vice Admiral
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Apr 20, 2014
Messages
5,657
The Begginer said:
Thanks but i dont need a block just wondering about the flaws of these 470s and what are the fixes
Click to expand...
Assumed u needed to rebuild engine due to knock…

head gaskets prone to blow in minor overheat
cam drive water pump - cam snout wears from seals leaks af into oil needs speedi sleeve
alternator conversion kit needed when voltage regulator dies

you may face some parts nla due to age but there are several folks that successfully run theirs for years
 
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