Back With The Wounderful 470

[CAPTKEV85]

Well all summer I had an over heating issue about 15 minutes being under a load. 3000rpms the boat would run great. push it a little more and about 5 minutes a 3500 she would run hot and then push antifreeze out of the resivour bottle. This motor is driving me nuts. I did another compression test and all cylinders are around 125 psi. then i performed a leakdown test no bubble in the antifreeze. Replaced the sea water pump and new heat exchanger. Now I hauled the boat and ran her on fresh water. no syptoms what so ever. What the hell is going on. please help

 

[abj87]

Re: Back With The Wounderful 470

It wouldn't show up on the hose because there is no load on the engine.
Is the heat exchanger the 3in or the 4in?
Did you test it with the new heat exchanger its hard to tell from your post?
Is the exhaust riser clear? its one of the only things left. Since it runs fine at low speeds im guessing the coolant side of the system is just fine.

 

[Rocky_Road]

Re: Back With The Wounderful 470

You might want to check to see if you have the correct plate, between the two gaskets, at the exhaust elbow.

This plate is necessary for a closed loop setup.

You might also want to check the thermostat...make sure that someone hasn't removed it from the system.

 

[180shabah]

Re: Back With The Wounderful 470

You replaced the seawater pump - how did the impeller look? Any missing pieces? If so, did you retrieve them all?

How old is your exhaust elbow? Average life span in salt water is 5 years. When they deteriorate two things can happen, the water passages get clogged which causes overheating.....Or they rot through allowing water to drain back into the cylinders via open exhaust valves.

If you haven't pulled and inspected the elbow, do so now. Failure is not an option.....at least not a good one.

 

[CAPTKEV85]

Re: Back With The Wounderful 470

i replaced the stat riser and i have a new 3" exchanger. I replaced the seawater pump. the impeller was had cracks but no missing pieces. I rebuilt the lower half of this motor of this year. its been bored .030 over. since its a larger bore could i need to upgrade to a 4" exchanger. I dont know. All the spark plugs a clean as a whistle. no sings of losing antifreeze in the exhaust. but loose antifreeze whenever i go over 3000 rpms. it just overflows out of the bottle. I just wanna solve this issue so i can enjoy my boat again.

 

[TilliamWe]

Re: Back With The Wounderful 470

i have a new 3" exchanger.

Everything I have read about these engines say that you NEED the 4" exchanger.

You replaced the impeller, but did you replace the entire pump housing assembly? Have you backflushed the raw water side of the cooling system make sure there are no old impeller pieces still in it?

 

[cfelton]

Re: Back With The Wounderful 470

I would suggest checking the water intake on the outdrive for old impeller pieces and to upgrade to the 4 inch heat exchanger. Mine has been bored .040 over and runs about 160 at full throttle. When I replaced the raw water impeller I replaced the whole pump. I found that using about 1/2 qt. of Lucus oil stabilizer with my oil also makes better oil pressure and helps it run cooler!

 

[abj87]

Re: Back With The Wounderful 470

Hopfully you will be able to return the 3" and upgrade to the 4" merc switched over the 4" in the early 80 when it 3" was found to inadequate. I have the 4in and it NEVER goes over 160*!

 

[CAPTKEV85]

Re: Back With The Wounderful 470

ILL back wash the saltwater side this weekend. i i take the hose off the riser and rev the engine i can shoot a stream like 6 feet. also i bought the impeller kit the housing impeller the gaskets and the metal plate. I did notice the old white plastic tube was melted. I have a strong feeling its the heat exchanger. to small. cause this motor runs great. it moves my 26 foot proline at 35 mph estimaited by gps. but thes overheating above 3000 rpms is a killer.

 

[CAPTKEV85]

Re: Back With The Wounderful 470

well did another leakdown test today. and boy do i have a blown head gasket. Its blown between number 3 and 4 cylinder. pushing air into the coolant system. so i took the head off and you can see that the gasket pushed over. im sending the head out this week to be checked, and checking the block with a straight edge.