grouper249
Recruit
- Joined
- Jul 10, 2011
- Messages
- 3
First time posting, however many of the testing i've done to date have come from this forum. Thank you all!
Having an overheating problem that is unlike any other that i've tackled. Boat is a 1989 26 Shamrock predator with a 1996 mercruiser 5.7 MPI. Motor has a FWC half-system (block only) and was rebuilt 3 years ago and now has approx 350 hours. Manifold and Elbow are new from 2 years ago (200 hours). Original RWC hoses to the manifolds.
Problem first arose after a 2 hour cruise around tampa bay, when backing down to idle the temp gauge rose from 170 to over 200. I shut her down immediately, waited about 15 minutes, opened the heat exchanger cap, and noticed the HE was empty. refilled about 1 gallon of the 50/50 mix, placed the cap back on, and made it home at 160 degrees. Due note, i've run the boat about 4 times since, and the problem only surfaces when under load and at speed 3200 RPM's after running for 30+ minutes. The engine has been run above 3400 RPM's once since the rebuild.
To date, below are the tests i've gone through.
1) Confirmed RW pump, and associated hoses had no blockage and were "sucking" at appropriate rates (5 gallon bucket in 30 seconds at 700 RPM).
2) pressure tested the HEX (no leaks detected after 15 minutes at 15 lbs )
3) Compression test after engine warm up with biggest drop in compression 6% (165lbs to 155 lbs). No water in cylinders. Also no water in oil.
4) Purchased a exhaust leak detector kit from NAPA and it showed exhaust leaking into the HEX. Also have bubbles in the overflow tube exiting the HEX to the overflow reservoir.
what's puzzling me is compression checks out normal, however it appears i have exhaust gases entering the HEX, (test #4 above), and thus the coolant exiting out the overflow reservoir. When i did the compression check today. i noticed two spark plugs were "extremely" loose, only requiring one full turn to remove them from the block. Lastly, other than the overheating, the motor runs very smooth from idle to cruise with no misses inbetween.
What else could cause the "back" pressure other than a head gasket? Any help would be appreciated.
Jeff
Having an overheating problem that is unlike any other that i've tackled. Boat is a 1989 26 Shamrock predator with a 1996 mercruiser 5.7 MPI. Motor has a FWC half-system (block only) and was rebuilt 3 years ago and now has approx 350 hours. Manifold and Elbow are new from 2 years ago (200 hours). Original RWC hoses to the manifolds.
Problem first arose after a 2 hour cruise around tampa bay, when backing down to idle the temp gauge rose from 170 to over 200. I shut her down immediately, waited about 15 minutes, opened the heat exchanger cap, and noticed the HE was empty. refilled about 1 gallon of the 50/50 mix, placed the cap back on, and made it home at 160 degrees. Due note, i've run the boat about 4 times since, and the problem only surfaces when under load and at speed 3200 RPM's after running for 30+ minutes. The engine has been run above 3400 RPM's once since the rebuild.
To date, below are the tests i've gone through.
1) Confirmed RW pump, and associated hoses had no blockage and were "sucking" at appropriate rates (5 gallon bucket in 30 seconds at 700 RPM).
2) pressure tested the HEX (no leaks detected after 15 minutes at 15 lbs )
3) Compression test after engine warm up with biggest drop in compression 6% (165lbs to 155 lbs). No water in cylinders. Also no water in oil.
4) Purchased a exhaust leak detector kit from NAPA and it showed exhaust leaking into the HEX. Also have bubbles in the overflow tube exiting the HEX to the overflow reservoir.
what's puzzling me is compression checks out normal, however it appears i have exhaust gases entering the HEX, (test #4 above), and thus the coolant exiting out the overflow reservoir. When i did the compression check today. i noticed two spark plugs were "extremely" loose, only requiring one full turn to remove them from the block. Lastly, other than the overheating, the motor runs very smooth from idle to cruise with no misses inbetween.
What else could cause the "back" pressure other than a head gasket? Any help would be appreciated.
Jeff
