First post, so be gentle!
Yet another overheating
4.108. I've not had a problem with my engine
at all. Normal operating temp under all conditions. Went from zero problems to overheating
Here's what happened: After something like 45 minutes of normal running (1750 rpm), engine
suddenly overheated. I was more than fortunate to got the boat back to the dock
without too much trouble, but the engine would not run at anything more than an idle for more than 5-8 minutes before overheating again.
Here's what I did:
1. Checked alternator
belt - Intact and tensioned. Checked coolant
level- It was good. Checked raw-water flow - It was good. Checked the entire raw-water circuit for any obstruction, component failure or leakage. This included the through-hull, raw-water strainer, raw-water pump (including impeller), heat-exchanger and tubing stack. All is fine here. Normal flow, no obstructions, all parts
in good order and serviceable.
2. Begin to check freshwater circuit. First thing I suspected was a stuck thermostat. Removed same and replaced with a new one. Checked both the old and new one to make sure they were working. All fine. Installed new thermostat and gasket
and ran engine. Overheated immediately.
Perhaps a vapor lock? I drained all fresh-water coolant
from the system, removed the pressure cap from the header tank/heat exchanger, and the water-temp sensor fittings from the front and back of the cylinder head
. I added 50/50 coolant at the highest point (expansion tank above all hose runs) until coolant flowed out of the water-temp sensor locations. Refitted those and added coolant until it flowed out of the top of the header tank/heat exchanger.
Started engine, waited a few minutes until it was "warm" then backed off first the forward temp-sensor ensuring there was no air present, then the rear fitting. Engine overheated.
Perhaps a blown head-gasket or cracked head/block? No oil
in coolant or coolant in oil
. At least by visual inspection
of the dipstick, beneath the oil filler cap or in the coolant itself. Engine is not smoking abnormally (no clouds of white smoke or sweet-smelling exhaust). I checked the coolant with the pressure cap off to see if there was any bubbling. None. At least none I could detect visually.
Perhaps the freshwater circulation pump? It's not leaking externally, not making any strange noises. BUT, and here's the rub, there seems to be no freshwater circulating. Despite the engine overheating, the freshwater hoses all remain cold to the touch (water temp around here at this time of year is 44). The header tank/heat exchanger is too hot to keep your hand on, but the hoses are cold. Lift muffler
is cool. Injection elbow
Since the freshwater pump pulley and the pump vanes are press-fit onto the same shaft, if the pulley is turning, is not the vane turning as well? And if that's the case, shouldn't the pump be pumping?
So, my questions are these:
1. Can the freshwater pump fail so that it stops pumping coolant? I can only find reference to freshwater pump failures that include leaking fluid externally or oil internally. But nothing about them turning and not actually pumping.
2. Did I miss something or do something wrong when it came to bleeding the freshwater cooling
system? There doesn't appear to be any physical blockages in the system. I don't suspect any physical blockages as there is no indication of a gradual build-up of scale/sludge as the system never had a tendency to overheat. But no coolant flow would suggest an obstruction...
3. Can a blown head gasket
or cracked cylinder/block stop coolant from circulating?
I've been reading around this problem for a couple of days now without making any more progress or knowing what to try next. I'm at my wits end and would appreciate any thoughts or advice!