470 Mercruiser and the dreaded front seal

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nemyarbretlaw

Recruit
Joined
Oct 18, 2009
Messages
4
I have a 470 Merc that I bought in a 19 foot Renken from a guy not knowing of the dreaded front seal tendency to leak. (I am new to boating) After it was too late and I had bought it, I figured the front seal was leaking and I would have to R and R it. I bought a radiator pressure test kit and put it on just to be sure. What I found was that many of the hoses were loose and leaking. I tightened all of them, I put 16 pounds of pressure on the system and it never moved for 20 minutes. Do you think it was just the hose clamps or can a leak or blown head gasket not show up until higher pressures? The owner before me said it was getting warm and he pulled it out of the water. I found pieces of the impeller in the exchanger so that is why I tried a pressure test fearing a head gasket. Long story short, I bought two boats on auctions and will sell one so I am hoping this can just be serviced and sold. It has the original charging system, 4 inch exchanger and has not had the front seal done. Serial number is 6379025. The other boat is a merc 3.0 and does not scare me as much as the opinion of the 470's. What do you think. Thanks for the help. :confused:
 
ErieRon

ErieRon

Chief Petty Officer
Joined
May 5, 2009
Messages
463
Re: 470 Mercruiser and the dreaded front seal

If the front seal is leaking you will see it dripping from the weep hole at the bottom left of the pump housing.

As for the other stuff...sounds like it wasn't well maintained. To do it now would be expensive and time consuming, but not out of the question. Have you done a compression test on it yet? I think you need to do a little more discovery before deciding.

If the PO said it was running hot, and you found pieces of the impeller in the heat exchanger it likely over heated. These engines are prone to head gasket problems if overheated.

I would inspect and flush the raw water side and do a compression test first.
 
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nemyarbretlaw

Recruit
Joined
Oct 18, 2009
Messages
4
Re: 470 Mercruiser and the dreaded front seal

I did not run the compression check yet, I started but it is really hard to get at the back 3 plugs. The first one was 125lbs. I am just hoping that the thing is not sporting a blown head gasket or cracked head. I thought maybe since it did not leak any more it may have been loose clamps that the po thought was leaking. It is not leaking from the weep hole althought where the hoses were leaking first it was running down and appeared to be in that area. Thanks for the help.
 
Rocky_Road

Rocky_Road

Lieutenant Commander
Joined
Oct 8, 2008
Messages
1,798
Re: 470 Mercruiser and the dreaded front seal

nemyarbretlaw said:
I have a 470 Merc that I bought in a 19 foot Renken from a guy not knowing of the dreaded front seal tendency to leak. (I am new to boating) After it was too late and I had bought it, I figured the front seal was leaking and I would have to R and R it. I bought a radiator pressure test kit and put it on just to be sure. What I found was that many of the hoses were loose and leaking. I tightened all of them, I put 16 pounds of pressure on the system and it never moved for 20 minutes. Do you think it was just the hose clamps or can a leak or blown head gasket not show up until higher pressures? The owner before me said it was getting warm and he pulled it out of the water. I found pieces of the impeller in the exchanger so that is why I tried a pressure test fearing a head gasket. Long story short, I bought two boats on auctions and will sell one so I am hoping this can just be serviced and sold. It has the original charging system, 4 inch exchanger and has not had the front seal done. Serial number is 6379025. The other boat is a merc 3.0 and does not scare me as much as the opinion of the 470's. What do you think. Thanks for the help. :confused:
Click to expand...

If you are looking for an opinion as to which engine to keep...I have to vote for the 3.0L.

I have both a 470, and a 3.0L...and the 470 has been 'parked' for the past year, due to what I believe to be a head gasket issue. I admit that the 470 was the first of my two boats, and I have a 'soft' spot for the 470...but when I actually think objectively about the reliability, I know that I will have fewer (knock on teak) problems with the 3.0. My 470 has been resleeved at the cam and I was still losing coolant. One day I get around to 'fixing' it....

Do the compression check, and fire her up! Then...take the 3.0L out for a fun day on the water.

Happy boating!
 
ErieRon

ErieRon

Chief Petty Officer
Joined
May 5, 2009
Messages
463
Re: 470 Mercruiser and the dreaded front seal

Yeah, the last two plugs are a bear. Try a long extension with a universal joint between the extension and the socket...works for me.
 
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