Mercruiser 4.3 cracked intake manifold

[Lou C]

Also if the engine is level when you drain it (as it should be) and you pull the bottom end of that big hose on the circulating pump off, I'd be curious to see if there is any water in the intake if you then pull the plug. First few times I'd do both!
Even after pulling the block drains, disconnecting that hose drains a LOT of water, like a couple qts at least. I'm surprised it didn't crack before.
Also make sure to poke the block drains they do clog up.

Interesting, so the difference between the 2 intakes:
they both have the front water passage that allows hot water to flow out of the cyl heads and through the stat housing
BUT....
the Pre-Vortec has no hot water passage under the throttle body area...there is an exhaust crossover but no water flow there at all, it is ONLY right in front....look at my pic above of the pre-vortec intakes, under the throttle body area is an exhaust crossover, and that tin cover is to keep the oil from cooking off from the hot exhaust crossover in the intake manifold.
so that's why maybe water can get trapped on the Vortec....

 

[LWD]

disconnecting that hose drains a LOT of water, like a couple qts at least. I'm surprised it didn't crack before.

If this is the hose you're talking about, I have a drain port on it.

 

[LWD]

be careful with the intake gasket and make sure you use the correct torque specs, there were some mistakes in manuals on this because the pre vortec took like 30-35 ft lbs but the vortecs are much lower like 10 or 15, you have to check, or else you'll be back where you started (water in the oil!)

I was surprised how easy those bolts came off. Appreciate the heads up.

 

[Lou C]

If this is the hose you're talking about, I have a drain port on it.

View attachment 342027

yep that's it. Nice to have the drain port.

 

[LWD]

I knew my boat was high on the bow end, and it's also high on the starboard side. That would make it difficult for the water to drain from the passageway above the #1 and #3 cylinders. I have a feeling that was my downfall.

 

[Scott06]

I knew my boat was high on the bow end, and it's also high on the starboard side. That would make it difficult for the water to drain from the passageway above the #1 and #3 cylinders. I have a feeling that was my downfall.

View attachment 342037

Is that a water passageway or exhaust cross over? If that has raw water in it then yes that is what did you in. At this point get the sludge out and replace with kero and oil as quickly as possible, likely you will be ok bearing wise. Only one way to find out... be prepared to do 3-4 oil changes to get all of it out after yo get it running .

 

[Lou C]

Could be. I'm not sure why they changed from the exhaust crossover to the water heated passage but that's what they did. Come to think of it I had a Ford 5.0 V8 back in the '70s and it was the same, intake was heated under the carb by antifreeze. To prevent carb icing.

 

[Lou C]

Is that a water passageway or exhaust cross over? If that has raw water in it then yes that is what did you in. At this point get the sludge out and replace with kero and oil as quickly as possible, likely you will be ok bearing wise. Only one way to find out... be prepared to do 3-4 oil changes to get all of it out after yo get it running .

Vortec has no exhaust cross over. That's why you have to use an electric choke if you are using a carb. My old pre-vortec has a well type divorced choke that is heated by the exhaust crossover.

 

[LWD]

Is that a water passageway or exhaust cross over? If that has raw water in it then yes that is what did you in. At this point get the sludge out and replace with kero and oil as quickly as possible, likely you will be ok bearing wise. Only one way to find out... be prepared to do 3-4 oil changes to get all of it out after yo get it running .

After 3 days of draining, the sludge is about drained. I'm hoping the bearings are good, because I've decided to go that route. I'm looking for a new intake manifold (I don't see one through this site), gaskets, lots of oil, and a few filters.... So far, this is a best case scenario, and if it stays that way I will consider myself very lucky.

 

[Lou C]

These were marine specific manifolds, not used in auto applications (maybe only in trucks back in the '80s). You will find them on ebay and at places that sell new and reman engines.

 

[achris]

Yeah, dunno the reason, but it isn't a standard drain plug, and it's horizontal, and there's a lot of room in there for water to expand. Would be odd for omc to have a TSB and not merc if the manifold and potential issues are the same. Maybe @achris knows of one?

News to me.

 

[Scott06]

After 3 days of draining, the sludge is about drained. I'm hoping the bearings are good, because I've decided to go that route. I'm looking for a new intake manifold (I don't see one through this site), gaskets, lots of oil, and a few filters.... So far, this is a best case scenario, and if it stays that way I will consider myself very lucky.

I believe michigan motorz sells that intake

 

[Lou C]

They do as does Center State engines and others. eBay can be good as well, I found a couple of spares for my old pre Vortec that way and they are a bit harder to find than the Vortec intakes since they haven’t been made in like 25 years! Meanwhile my original still hasn’t rotted out even with salt water use since about 2000 or so....

 

[LWD]

I bought an intake off eBay from Michigan Motorz this morning. I called Michigan Motorz to verify the intake, but they only do free shipping off ebay. I bought 3 gallons of cheap 20w50 oil, 1 gallon of 25w40 Mercury oil, 4 oil filters, and gaskets for my distributor and thermostat. Also a couple cans of brake cleaner. The intake comes with gaskets. Hopefully 4 oil changes will do it.

I still need gasket sealer for the paper gaskets, and gasket maker for the front and back of the intake manifold. I think that should do it?

 

[nola mike]

You don't need any sealant for the gaskets

 

[Lou C]

Those gaskets (Vortec style) have a plastic base and a rubber style sealing ring, they also have locator tabs that fit into holes in the cyl head so you don't need sealer for them, unless you have pitting/corrosion around the water ports on the cyl heads. I think yours looked pretty clean. On the older pre Vortecs I use sealer because that keeps them from sliding around while you are trying to lower the manifold in place. The front and rear "china wall" parts of the block you use an RTV sealer that you run up the edge of the gaskets about 1/2" on each side.

 

[LWD]

You don't need any sealant for the gaskets

Not even on the thermostat or distributor gaskets? Just an FYI, I wouldn't use gasket maker on them. For some reason I thought sealant was used on one side, maybe that was mostly to keep them in place. Good to know though.

I see you used to own an '86 Glastron Conroy X-19, that was our first boat, it had the 140hp MerCruiser. We absolutely wore that boat out, some of our best boating memories!

 

[nola mike]

I see you used to own an '86 Glastron Conroy X-19, that was our first boat, it had the 140hp MerCruiser. We absolutely wore that boat out, some of our best boating memories!

Still have it, though the interior is redone with a different layout and the 4.3 replacing the 3.7

 

[LWD]

be careful with the intake gasket and make sure you use the correct torque specs, there were some mistakes in manuals on this because the pre vortec took like 30-35 ft lbs but the vortecs are much lower like 10 or 15, you have to check, or else you'll be back where you started (water in the oil!)

My new intake should be here Wednesday, so I'm cleaning my gasket surfaces and looking through the manual. I got to the torque specs and it says 35 ft. lbs., then I remembered your comment. Then found the service bulletin about it. So glad you made this comment....

 

[Lou C]

Glad to help out. The 35 ft lbs is for the pre-vortec that I have. I saw that bulletin as well, I'm not sure who made the mistake (GM or Merc) but yes there was confusion about that. Its because the composition of the gasket changed, the older ones were not as sensitive to overtorquing, the new ones are a plastic/rubber type composite and over-torquing them can distort the rubber or break the plastic.