1985 omc 3.0 140hp issues

[misiek]

I need some advice. I have bought this 17' 1985 Thundercraft with 3.0 OMC 140 HP engine with some issues. The engine starts and boat gets going nicely but when I stop and turn off the engine I have problems starting it again. What seems to help is to lift off the engine cover. Once the engine starts going again it runs very well again. Can this be an air/fuel mixture problem? I know that I have a small leak in the exhaust manifold. Water drips from under the gasket. Does this have anything to do with it? The engine temperature gets up to 160 when running at full throttle for a while. Is this the normal operating temperature? Please advise. I am very new to this type of engines.

P.S. What can cause a new gasket to blow from under the exhaust manifold?

 

[zbnutcase]

Re: 1985 omc 3.0 140hp issues

As there is no water passages between head and manifold on thoses engines I would be taking a closer look. Those blocks tend to crack if frozen up behind manifold where you can't see it.

 

[misiek]

Re: 1985 omc 3.0 140hp issues

So is it the cracked exhaust manifold or the cracked engine block?

 

[81 Checkmate]

Re: 1985 omc 3.0 140hp issues

Pull the plugs and see if water is in the chambers. Then you can go from there.

 

[misiek]

Re: 1985 omc 3.0 140hp issues

I have a cracked block, just in the middle under the exhaust manifold. What are my options at this point? Thanks.

 

[coheej]

Re: 1985 omc 3.0 140hp issues

Usually you replace the block. You may want to price a replacement motor.
It can be welded, but it has to be done by some good at welding cast iron.
The cost to weld mine was $600. I found a replacement block instead.

 

[misiek]

Re: 1985 omc 3.0 140hp issues

I'll try welding first but where do I go to find a replacement block? Thanks.

 

[misiek]

Re: 1985 omc 3.0 140hp issues

What engine can I replace this one with? What can I swap it out with without any modifications to the out drive or anything else? Please advise. Anyone with the same experience? Can you swap it out with a 2.5 OMC without any mods? Help out please!!

 

[tschmidty]

Re: 1985 omc 3.0 140hp issues

Yes you can swap for a 2.5. But I would look at JB Weld on that crack first.

Trouble with hot starts is not uncommon on these engines.

160 Is not a bad temperature to be running at.

 

[misiek]

Re: 1985 omc 3.0 140hp issues

I tried to JB Weld it. Looks good. No leaks. No oil in the water. Good compression on all cylinders. Looks like the block is only cracked on the outside. How long do you think the JB weld will hold? Anyone with similar experience?