dwheeler7676
Cadet
- Joined
- Dec 26, 2007
- Messages
- 14
I have a 1990 Mercruiser 5/0LX, std. (raw water) cooling, that is having temp problems, currently running too cold (~110 deg) all the time.
History:
1996-2006: Boat ran great, temp always read ~160 deg solid (brackish waters of upper Chesapeake Bay w/fresh water flush end of each day).
2007-2008: Boat layed up (gas tank replacement, new starter, manifolds, eng. circ. pump, belts, t-stat).
June 2009: Finally de-winterized, ran hot at idle (to point of overheating), but okay at any RPM above that.
July 2009: Serviced lower unit (noted impellor missing 1/8th of one blade), replaced W/P body and impellor. Temp now fluctuates on low side, but never overheats.
August 2009: After limited (~6) hours, unit now runs cool constantly. Pulled and checked t-stat housing and t-stat (140 deg), all clear, no blockages. Swapped out t-stat housing (including new t-stat and different temp sender), NO CHANGE! ALWAYS COLD! (~100-110 deg).
Note-1: Temp gauge every so often will fluctuate momentarily, 110-180 deg in a matter of seconds, but always return to the cold state. This is hard to verify with a IR thermometer, but I do think I see it, albeit delayed and damped by the thermal mass of the metal t-stat housing. (Intake manifold temp reads ~140-150 deg next to t-stat housing, risers only ~130-140)
Note-2: If I grab hold of the large hose running between t-stat housing and eng. circ. pump, I feel a pulsation, like a sporadic popping - hard to discern if it's metallic vibration, or if the hose is connected to a passage where water is boiling (?) - hose is only warm to the touch, even after running 15-20 min. I need to try this upon first start up, before engine "warms" up.
Questions: Can a blockage (impellor parts/rust chips/etc) working its way through the water system cause UNDER-heating? If so, WHERE is the most likely place(s) to look? Anyone seen this condition before? (Overheating seems all too common... and no, t-stat is not stuck open, mechanically anyway.) Can a blockage [say, in the block] cause back pressure from the eng. circ. pump to "force" the t-stat open [thereby "fooling" the temp sender]?
Please advise, and thanks in advance.
History:
1996-2006: Boat ran great, temp always read ~160 deg solid (brackish waters of upper Chesapeake Bay w/fresh water flush end of each day).
2007-2008: Boat layed up (gas tank replacement, new starter, manifolds, eng. circ. pump, belts, t-stat).
June 2009: Finally de-winterized, ran hot at idle (to point of overheating), but okay at any RPM above that.
July 2009: Serviced lower unit (noted impellor missing 1/8th of one blade), replaced W/P body and impellor. Temp now fluctuates on low side, but never overheats.
August 2009: After limited (~6) hours, unit now runs cool constantly. Pulled and checked t-stat housing and t-stat (140 deg), all clear, no blockages. Swapped out t-stat housing (including new t-stat and different temp sender), NO CHANGE! ALWAYS COLD! (~100-110 deg).
Note-1: Temp gauge every so often will fluctuate momentarily, 110-180 deg in a matter of seconds, but always return to the cold state. This is hard to verify with a IR thermometer, but I do think I see it, albeit delayed and damped by the thermal mass of the metal t-stat housing. (Intake manifold temp reads ~140-150 deg next to t-stat housing, risers only ~130-140)
Note-2: If I grab hold of the large hose running between t-stat housing and eng. circ. pump, I feel a pulsation, like a sporadic popping - hard to discern if it's metallic vibration, or if the hose is connected to a passage where water is boiling (?) - hose is only warm to the touch, even after running 15-20 min. I need to try this upon first start up, before engine "warms" up.
Questions: Can a blockage (impellor parts/rust chips/etc) working its way through the water system cause UNDER-heating? If so, WHERE is the most likely place(s) to look? Anyone seen this condition before? (Overheating seems all too common... and no, t-stat is not stuck open, mechanically anyway.) Can a blockage [say, in the block] cause back pressure from the eng. circ. pump to "force" the t-stat open [thereby "fooling" the temp sender]?
Please advise, and thanks in advance.