I'm about to blow this **** boat up( please help)

[mercrude]

1983 mercruiser 485 185 hp i/o<br />boat has been overheating I checked t-stat, changed impeller& pump in lower unit still overheating very quickly took boat to dealer/marine they suspect a blown head gasket cylinders had compression that varried from 105lb to 125lb. I do have two questions #1 what would cause the head gasket to blow. #2 how can I back flush cooling system to make sure none of the old impeller is blocking any passages. thanks for any information and GOD BLESS ALL

 

[Bondo]

Re: I'm about to blow this **** boat up( please help)

mercrude,<br /><br />"#1 what would cause the head gasket to blow.??" #<br /> overheating !!!!!!!! <br />To Test for a headgasket, You should be getting Alot of Pressure,+ Bubbles in your Heatexchanger.... Attach a Cooling System Pressure Tester on the Cap,+ Look for a pressure Rise...<br /><br />" #2 how can I back flush cooling system to make sure none of the old impeller is blocking any passages??"<br />Disconnect the line coming From the outdrive,+ Run the engine.....See if there is Water Flow.... If Not.... Work your way back from there.... You May have to Drop the Lowerunit.....

 

[mercrude]

Re: I'm about to blow this **** boat up( please help)

Bondo, thanks for your reply, I'm very aggravated with this boat its been one problem after another I'll try what you suggested the dealer did a compression check and the cylinders were 105-115-125-125 they all should be 150lb I believe

 

[Bondo]

Re: I'm about to blow this **** boat up( please help)

If they were All 115psi it Wouldn't Necessarily be a Bad Thing, But it Sure Looks like you have a Problem.....<br />I Wish I could help you more, But I know very little about the 470s.....

 

[a.d.mobile]

Re: I'm about to blow this **** boat up( please help)

how about removing both end caps on the heat exchanger and flush it out with a hose. anti freeze will not come out while doing this. these tend to hold a lot of sand and mud.

 

[Northern Eclipse]

Re: I'm about to blow this **** boat up( please help)

Mercrude after the compression test was done, has a leakdown test been done yet, this will tell you if its a head gasket or rings or valves.

 

[flashback]

Re: I'm about to blow this **** boat up( please help)

Got one question? what makes you guys think this is a closed system with a hear exchanger? I don't know anything about a 485 185hp. but mercrude did not say anything about a closed system......I'm guessing this is a 305 with a 4 barrel carb. just my 2 cents but I think you have some blockage in the system, if it is raw water cooled, I would suspect the power steering cooler being blocked up first...then work your way back thru the outdrive........good luck

 

[DJ]

Re: I'm about to blow this **** boat up( please help)

Flashback,<br /><br />All the 470's and 485's were closed systems. They are an aluminum block with a cast iron head, thus the closed system. They are four cylinder engines in the 3.7 liter range.<br /><br />Mercrude,<br /><br />I would be looking for a h-gasket leak between #1 and 2.

 

[Northern Eclipse]

Re: I'm about to blow this **** boat up( please help)

djohns19 is right the 470 was 2bbl carb rated at 165hp and the 485 was a 4bbl rated at 185hp, Mercrude Flash also a point about backflushing, you probably don't have power steering, but the voltage regulator are sea water cooled and are located up under the manifold on the side of the block port side if course. My Pops owns a 3.7 165hp That I take care of for him in 13 years never missed a beat. The trick to these motors is to keep it cool and well tuned. Anyway mercrude get a leakdown test done, as I stated in my previous post and good luck.

 

[worley1]

Re: I'm about to blow this **** boat up( please help)

I have torn the motor apart to change the head gasket. Question #1 should I take the head some where and have it tested or should I just put it back together and torqe to specs

 

[flashback]

Re: I'm about to blow this **** boat up( please help)

learn something new everyday, boy am i dumb... thanks for the info dejohns19......good luck to you, Mercrude.........

 

[worley1]

Re: I'm about to blow this **** boat up( please help)

I forgot to mention when I took off head there was no water on top of pistons or rust on cylinder walls how do I know if the head gasket was blown?