1994 74L Mercruiser Coolant Problem

"I have a '94 Sea Ray with

"I have a '94 Sea Ray with twin 7.4L Mercrusiers - I have had issues this past season with both engines heating up from 160(idle) up to 180(higher speeds)they cool back down after I slow down. When this happens there appears to be more than normal steam coming out of the exhaust. I changed the thermostats, impellers,oil coolers, risers/elbows. It is a closed system. I had to clean the intakes under the boat every other week due to growth.
I noticed that one engine, after sitting for a couple of weeks - when first started & just as water begins to come out the exhaust I noticed a small bit of coolant that comes out...for a second..just a splash. There appears to be a bit of steam that smell of collant for about a minute and than it goes away.
A few people have suggested that I either service the Heat Exchangers or replace - The thought is that the collant in the exchanger could be slowly leaking into the fresh water and out of the exhaust when that engine is started.
The engines run great & I do not have collant in the oil. I'm hoping that it is not a head problem.
Does the appearance of coolant upon start up sound like a possible Heat Exchanger problem? I purchase the boat 3 years ago - doubt that they have ever been serviced.
Any suggestions would be appreciated

Michael"

"Mike,

Do you have to add c

"Mike,

Do you have to add coolant to that engine occasionally?

It could be a heat exchanger, it could also be a riser blockoff plate or gasket. These are the only two locations where the raw and fresh water could mingle. As far as your operating temps and steam, I don't see anything abnormal about what you are experiencing. 180 is certainly not too hot and under a load the engine is going to generate more heat than it idle. You can test the integrity of the system by draining the coolant and connecting a cooling system pressure tester. Pump it up to 5 psi and let it sit for an hour. If it doesn't show any drop in pressure take it to 15 PSI and let it sit again.

A cooling system leak will show up if it does exist. If you find it to be leaking, but can't identify where, I would replace the blockoff plates and gaskets and try again. If it solves the problem, bingo. If not, I would remove the exchanger and take it to a reputable radiator shop for testing and repair.

Good luck
Rick"

"Thank you Rick,
I have had t

"Thank you Rick,
I have had to add coolant directly into the exchanger a few times - unfortunatly I did not have the opportunity to use the boat that much this past season...so I cannot be more specific on how much I had to add. I did not pay that much attention to it.
I had changed the riser gaskets about a 3 month ago. I will double check to make sure the bolts are tight. I'm going to focus on the heat exchangers at this point. I do not believe that they were ever serviced...11 years. Do you know if there is a specific hose that I would hook the pressure tester up to - there are like 5 hoses coming out of the exchanger. I would assume that I'm trying to find out if the coil tubes inside the exchanger(salt water)are holding the pressure? If not they might have a pin hole allowing coolant to enter the salt water tubes? If there was a pin hole..couldn't the salt water get into the coolant? I'm thinking I should just remove the exchangers and have serviced.
I appreciate your help.
Michael"

"I use the Snap-On tester whic

"I use the Snap-On tester which has an adapter to connect directly in place of the cap on the heat exchanger. If you don't have this tester, or one similar, available you can tap into any of the hoses or drain fittings in the closed side of the system. It is much easier to test this with the system intact, although you will want to drain the coolant first. Yes it is possible that seawater can enter the exchanger through a pinhole, but it is much more likely, due to the operating pressure that it will leak the other way. Sending coolant out and into the discharge side of the seawater system. Although it's not a bad idea to have the heat exchangers cleaned and checked, I would still rather know where the problem is first.

Keep us abreast on your progress.

Rick"

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