‘85 190hp 3.7L blown head gasket

[Myride85]

Bought this POS boat a few months ago and nothing but issues. Hit the lake 3 times for testing purposes. Had a low rpm, wouldn’t plane at all. New prop, tune up. Found a vacuum hose off for the choke. BUT, the main issue is it’s a closed cooling system and I’m loosing coolant, fast
Did a pressure test on all 4 cylinders. With all the plugs out. I placed my air hose into each cylinder, the tip has a rubber tip to fit perfectly in the plug hole. Well #4 is leaking air back into the coolant tank. I’m guessing I now have a blown head gasket. I’m pretty good on fixing things. But am I over my head now? Also found the exhaust manifold exhaust port between the 2 chambers for the exhaust, it’s cracked need good recommendations on a good site etc for parts for this rebuild. So tempted to pull the motor out and have it rebuilt. If that is an option I want to do. What would be a going rate to have it completely rebuilt? Top to bottom
Thanks everyone

 

[Eric 3.7LX Alpha 1]

These engines have a Mercruiser aluminum block mated with a Ford 460 cast iron head. They also use the 460 rods and pistons so they have a big bore and good torque, and fuel economy is good with them. They are very sensitive to overheating. The different expansion rates of the two metals almost always causes a blown head gasket if it overheat.

The earlier versions where made with a 3" diameter heat exchanger that was later replaced with a 4" for better cooling. You will want a good temperature gauge at the helm, and stay on replacing the impeller in the drive every few years.

Personally I wouldn't do a total rebuild unless it was necessary. Coolant can also leak out the drive water inlet if the heat exchanger has damage from not winterizing soon enough. You'd see antifreeze running down where water gets drawn into the drive.

I would fix what is broken, and run it. There is plenty of other ways so spend money into the boat.

 

[Scott Danforth]

the head is a modified for 460 (it has a big ol hole drilled in it)

if you want to rebuild the 470, suggest you add a bore stabilizing spider (sometimes called a deck girdle) to the block and get an edelbrock aluminum head for a ford FE engine. you will also need to sleeve the bores

as Eric indicated, these things are sensitive to over heating. the open deck (floating bores) and the aluminum block/iron head means as little as a 10 degree overheat and you will loose the head gasket

there are other design flaws with the engine

I also would not rebuild unless needed, as the cost to get the block sleeved, modify the block, new pistons, rods, bearings, head, etc, brings the price of a rebuild over $2k. swapping to a 4.3 is also an option.

plenty of places to buy exhaust manifolds and elbows hold on to your hat when you see the price. the elbow isnt bad at $300, however the exhaust manifold is over $1200 most places

 

[Myride85]

Thanks all, was thinking of just a complete rebuild as my season is about done here in MN doing it during the winter time.
Holy shi** $1200 for the riser? Damn. I’ll snap a pic in a min and post it what I see wrong

 

[Myride85]

Pics of the exhaust manifold.
I know that's not my main issue. But it's still a problem

 

[Scott Danforth]

you need a new manifold. its the manifold that is $1200

 

[jhamblett]

you need a new manifold. its the manifold that is $1200

No other options?

 

[Scott Danforth]

No other options?

You may find used.

However used manifolds are like buying used depends......


Remember, boating is an expensive hobby, and $1200 for an aluminum manifold that is no longer available from the manufacturer is a deal

 

[jhamblett]

You may find used.

However used manifolds are like buying used depends......


Remember, boating is an expensive hobby, and $1200 for an aluminum manifold that is no longer available from the manufacturer is a deal

That's why I asked, I thought there was a aluminum option.

 

[Eric 3.7LX Alpha 1]

Yes you can switch to the aluminum version, that's what I have. You also have to replace the riser/exhaust elbow/reservoir if you switch to Al. They are different. I replaced mine probably 15+ years ago, they where a lot cheaper back then.

 

[Myride85]

Any leads on where to see the aluminum riser and the coolant reservoir?

 

[Myride85]

Having a hard time to find the combo I need. Can not find a cast iron manifold. Can find aluminum manifold, but can’t find the reservoir for the aluminum. Any ideas or leads on where or who to look up?
thank you

 

[Eric 3.7LX Alpha 1]

Here is a new riser for sale on ebay for the aluminum manifold. It's not cheap but it's brand new. There are some used one's out there you can also try to take a chance on.

Mercury Marine Mercruiser New OEM, 165 HP Exhaust Elbow Assembly, 98562A6 | eBay

Find many great new & used options and get the best deals for Mercury Marine Mercruiser New OEM, 165 HP Exhaust Elbow Assembly, 98562A6 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[Eric 3.7LX Alpha 1]

Here is a brand new aluminum exhaust manifold they have listed as an intake. The price is cheaper than other new one's I've seen. There are also used exhaust manifolds out there. You can try used, you may get lucky but it's a gamble.

Mercruiser Intake Manifold 816219A 4 | eBay

Casting number on the manifold is 816219C. Fits 3.7 170/ 470. Includes thermostat and housing and temperature sending unit. Gaskets are NOT included. Don't see what you are looking for?.

www.ebay.com

 

[Myride85]

Really beginning to think. Is the crack in the chambers separated a really that big of deal to replace? It’s just the exhaust. It’s not broken and it Leads into 1 chamber at the riser.

 

[Scott Danforth]

the crack in your exhaust will allow water to come back, run down the exhaust and fill your cylinders.