Logo
FULL SITE MENU

Narrowing down antifreeze leak hunt

M

mark_searay

Contributing Member
"Hello and thanks in advance f

"Hello and thanks in advance for all your help.

Boat: “rescued” from in-laws, poor maintenance history from poor marina, this is our first year with boat, moved it from MN to Ozark.
1985 Sea Ray SRV255 / Twin 170’s – stern drive / ~ 1100 hours ea. previous owner ran 98% of hours at 1200-1800 rpm.

55 hours this summer, full range of rpm operations – consistent AF loss from header tank in typical outing of 1-3 hours = loss of 0.5-1.0” down from radiator cap.

Operating temp is in normal range per gauge at all rpm’s.
Over flow tank always full, will not draw back to header tank, radiator cap good.

NO leak from cam/pump weep hole, weep hole is open with packing grease still evident.
Minor leak evidence from bottom of circulating pump gasket, damp AF crystals at gasket, bolts tight. No leak evidence on heat exchangers or any AF hoses.

No evidence of AF on plugs.
Pressure test, 5 hours at 15 psi, no leak, followed by 1 hour at 18 psi, no leak down.

Only significant AF leak evidence is from spray out of overflow tank cap at the tube connection port on top of cap.

No cylinder compression test yet. This is the starboard engine, port runs a bit cooler (about three needle widths, gauge is not numbered) engine warms up per gauge in 5 minutes, port takes about 10-15 minutes.

Thoughts anyone? Which expensive part is this and is there a method to isolate which gasket?

Thanks, Mark"
 
"Port engine needs a new T&#39

"Port engine needs a new T'stat.; too long to warm up.

"Over flow tank always full, will not draw back to header tank, radiator cap good"..."leak evidence from bottom of circulating pump gasket"

Engine needs a circulating pump kit for starters.

"Only significant AF leak evidence is from spray out of overflow tank cap at the tube connection port on top of cap"

Since the engine will not vacuum back into it the expelled antifreeze from normal operation, the air pressure in the block is causing the overflow tank to expell antifreeze from the full overflow tank. Rebuild the circ. pump, replace the main tank cap and the problem should be resolved unless there is a "temperature" related antifreeze leak. With an aluminum block you may have a hairline crack in it or just a defective head gasket. Your pressure tests say you don't. Did you test it with a cold or hot engine?

Consider examining the exhaust manifold and gasket. Antifreeze may be going out with the exhaust."
 
"Thanks Guy,

Coolant pressu

"Thanks Guy,

Coolant pressure test was done with engine cold and in dry dock.

Will replace the radiator cap this weekend and report back results. Will also run boat with radiator cap removed and check for bubbles in the header tank.

Will put new pump kit in during winterization in ~3 weeks and replace port thermostat at same time.

Is it possible that a potential head gasket leak is driven by compression/exhaust pressure and the 15-18 psi leak test would not catch it? (a one way leak?) And a compression test would catch it?

Other than external visual exam of exhaust manifold how to "check it" other than removal of the manifold?

Thus in diagnostic sequence:
1 radiator cap
2 bubbles in tank during operation
3 cylinder compression test
4 exhaust manifold removal, all new top end gaskets, maybe EX manifold
5 block?


Thanks, Mark"
 
"Mark:

You can improve the

"Mark:

You can improve the leak finding process by adding dye to the antifreeze and run the engine awhile. Then use a black light to see the glowing dye where it is leaking.

Anything can happen to gaskets between dissimilar metals when they are heated; in this case an aluminum block and iron head. This engine is notorious for blown head gaskets.

Check the tank pressure while the engine is warm and see if it holds. Also perform dry and wet compression tests on the warm engine and post the results.

In the parts diagram see items 23 and 27. Check to see if they are plugged. If you remove the EXHAUST ELBOW AND RESERVOIR ASSEMBLY you can get a good look at the gasket and the exhaust manifold.

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=%2012488&ivar=images/CRUI SER/12488/23.png&inbr=908&bnbr=110&bdesc=EXHAUST+MANIFOLD+AND+EXHAUST+ELBOW+%28C AST+IRON%29"
 
Back
Top