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Coolant Disappearing

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dbriceno

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I recently changed manifolds &

I recently changed manifolds & risers on my 1998 Mercruiser 7.4's inboards. Since then whenever I run the boat my starboard engine heats up slowly and will occasionally overflow the overflow tank. Even when that doesn't occur as the engine cools I lose at least a quart of antifreeze. I replaced the heat exchanger cap with a lower pressure cap and the amount of lost antifreeze has decreased to a pint or so. Where is it going? I pressure tested the heat exchanger and looked to see if any coolant was leaking into the raw water side with no luck. The pressure does seem to slowly drop. My oil is fine. Can coolant be leaking into the exhaust manifold and out the exhaust as the engine cools? Any thoughts will help. I'm considering having the heat exchanger looked at and serviced but it seems that it must be related to the manifold job that I did.
 
What brand of manifolds did yo

What brand of manifolds did you install? There is a Chinese made one that has casting porosity problems and poor mating surface machining; name escapes me? If it won't hold pressure there is a leak somewhere. You can put some dye in the antifreeze to see where it's going.
 
The manifolds are GLM Marine.

The manifolds are GLM Marine. Are the mainifolds raw or fresh water cooled? I thought they were raw water cooled and that there wasn't any fresh water in the manifolds or risers. Do you know one way or the other?
 
"If the oil cooler has a leak

"If the oil cooler has a leak then the antifreeze will leak into the engine cooling and be discharged ouver board. If the manifolds were leaking then you (may experience a hydroloc situation.) Since this has not happened then i think that one of the follwing may be happening
1)the oil cooler is in question
2) If the elbow sits on an extention block, the entention block may be leaking(if it has not been changed.)
3.The manifold is not mated properly to the block(rare) because anti freeze would be leaking into the bildge.
4)Check the hoses to the risers and the manifolds for leaks."
 
GLM are the problem manifolds.

GLM are the problem manifolds. When you put them on did you use solid gaskets between the manifold and riser/elbow? That would mean the manifolds are FWC. If the gaskets were slotted then they are RWC. Pressurize the cooling system to 16 lbs. and listen to the oil fill cap opening for gurgling. Pull the rubber coupler sleeves from the exhaust elbows and listen there for the noise. The feed/return hoses on the manifolds can be pinched w/a needle nose vice grips to isolate them to see if the pressure holds.
 
Check the weep hole on the bot

Check the weep hole on the bottom of the engine circulating pump. There may be a hole in the heat exchanger tube.
 
Did you purge all the air from

Did you purge all the air from the cooling system when you renewed the exhaust?
 
"If the t-stat hoses go to the

"If the t-stat hoses go to the manifolds (bottom) and the hoses at the top of the manifolds go to the heat exchanger, the manifolds are in the coolant side. As Guy asked earlier, there are 'different' gaskets for the elbows; these keep the coolant and the raw water from mixing. Those hoses leaving the t-stat housing are the usual place for the air to collect. With new manifolds, you can figure they were dry, too.

I don't have a manual for the '98's, so I can't get you the specific bleeding procedure. The easiest thing is to keep checking it after running it. If you keep the overflow bottle filled to the FULL line, the remmaining air should be bled out over the next few runnings.

As long as the amount you add keeps decreasing, you should be ok. If you suddenly have to add more, something else is going on.

Put the factory rated pressure cap back on after you test it with the pressure tester. They have a valve that will allow coolant to flow back in as the system cools."
 
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