Mystery coolant leak

[koresample]

7.4 L MPI FWC motor in the 98 270 DA has started a mystery coolant leak. I say mystery becasue I filled the overflow to the 'cold' line and ran the boat for about 5-6 hours. After the motor cooled down (and for a couple of days) the coolant level in the overflow pretty much stayed at the same level. I checked on the boat last night and happened to see that the level is down a couple of inches now.

I don't see any coolant in the bilge or behind the motor or under the overflow bottle....any suggestions? There is no white smoke when I start the motor and I had the manifold, risers and gaskets replaced 20 hours ago. I double checked the bolts on top of the risers and they are torqued down correctly. All that would make sense if it was losing coolant when the motor was running...but when it's sitting?

 

[hottoddie]

You may not have actually lost any coolant at all. The system has several gallons in it and as the motor cools the AF in the overflow tank is drawn back into the block. If the outside temp rises enough and the block warms up it will push it's way back out into the overflow tank. My big block Crusader's took 30-40 running hours to completely get all the air out of system. I thought I had leaks but they were just slowly getting back to normal. Keep an eye on it for a while and most likely it will level off and hold steady.

 

[koresample]

You may not have actually lost any coolant at all. The system has several gallons in it and as the motor cools the AF in the overflow tank is drawn back into the block. If the outside temp rises enough and the block warms up it will push it's way back out into the overflow tank. My big block Crusader's took 30-40 running hours to completely get all the air out of system. I thought I had leaks but they were just slowly getting back to normal. Keep an eye on it for a while and most likely it will level off and hold steady.

Thanks for the reply - so, should I top it off again back up to the 'cold' line? I had thought about air in the system as I had a BUSS heater that I had disconnected because they installed the unit above the level of the overflow and it was causing the rad cap to leak. I would assume the mechanic had bled the system but assuming is not always a safe idea.

 

[northern]

Both my engines do the same. It is not normal. I feel mine is caused by the heat exchanges. I had them both rebuilt and the loose increased a bit. I have a Jet Boat that had the same problem and I got a new heat exchanger and it stopped the problem. When I replace the risers and manifolds next I will replace the heat exchamgers. Until then a gallon or so of anti freeze cost less than new heat exchangers.
Losts of post on this you should look them up as it will give you some good information and point out other things it could be.