Where to Look For Cooling/Water Flow Problem?

[minuteman62-64]

Motor: 1982 Mariner 30A. Wasn't used for about a year. Ran OK when last used.

Started it up a week or so ago, in a barrel. Ran OK at idle and about 1200 rpm for maybe 10 minutes, with normal temperatures (based on my cylinder head sensor) and good flow from tell-tale. Then, running at idle, tell-tale flow petered out to just a dribble and motor over heated.

OK, I know this drill. Impeller over a year old, sitting for a long time, needs replacing. Installed new impeller and put motor thru its paces in barrel. All OK.

Thursday took it out to Mission Bay (San Diego) for a victory lap. Everything good to start. Then, on a long run (maybe 30 minutes) in the 5 mph zone, the head temperature started drifting up a bit. Still decent flow from tell-tale, both at idle and when I goosed the throttle a bit just to test it.

On the return leg, about half way back, overheat alarm went off and flow from tell-tale stopped. No kelp clogs so waited awhile and started up again. Tell-tale flow to start, then tapered off to nothing.

Limped back to the landing with help of tail wind and intermittent motor thrusts. Sat at the dock for about 15 minutes then it started up with modest tell-tale flow and ran enough to get on the trailer.

Back home, I pulled the lower unit expecting a messed up impeller. Nope, impeller was in great shape.

Where do I look for problem?. Seems to be a combination of intermittent pumping after warm up and low water flow in general.

 

[QBhoy]

Hi
i didn’t think these had an alarm in those days, but regardless, maybe if it is in sea water, your channels are clogged with crystallised salt. Seen this a few times. Take the tell tale pipe off at its source on the head and see if it pumps water out there. Often the tell tale pipe gets clogged, but not often the main cooling flow does.

 

[minuteman62-64]

Hi
i didn’t think these had an alarm in those days, but regardless, maybe if it is in sea water, your channels are clogged with crystallised salt. Seen this a few times. Take the tell tale pipe off at its source on the head and see if it pumps water out there. Often the tell tale pipe gets clogged, but not often the main cooling flow does.

I added both the alarm and the cylinder head gauge a few years back (with assists from some of the guys on here). No tube to tell-tale. Near as I can tell there is an internal passage from somewhere where the water tube enters the head.

Anyways, my next step will be to begin squirting water up the water tube and down thru the thermostat housing to see if it seems open. Then test the thermostat.

What confuses me is that, on the Bay run, it pumped for about 30 minutes and then flow started to shut down and eventually stopped. I'm hoping something will blow out during the water squirting that might be the cause - but not optimistic.

 

[minuteman62-64]

Well, found a smoking gun and maybe a couple of spent cartridges.

Squirted water through the block/water tube in all possible directions. No indication of any stoppage. I also scoped the LU from the water pump base down to the water intakes and up the water supply tube. No problems noted. Finally, checked compression. Upper cylinder 136, lower cylinder 135 - within 1 psi of what I got about 5 years ago so I'm hoping that's a sign of no head gasket problems.

However, when I did the thermostat test (supposedly a 140 degree unit) it didn't open till 165 degrees and then closed back down at 150 degrees. There was also some crud (salt/corrosion/sludge) that seemed like it would restrict flow thru the thermostat when it did open. OK, maybe major problem solved.

Two other issues I noticed. First, the metal cartridge (that holds the impeller) was sticking out of the pump housing further than the thickness of the gasket. Result was that any sealing of the impeller housing was being accomplished by metal to metal contact between the cartridge and the bottom plate. I am assuming this is not a good thing. I had another housing (OEM, I believe) and checked that. A lot less projection, but, the gasket supplied was still not thick enough to prevent metal to metal contact. So, I've switched to the OEM housing and hand cut a thicker gasket that will actually provide a seal and will try that.

The second issue I noticed when I pulled the pump's bottom plate. No gasket underneath - just a few shreds of silicone "form a gasket." I remember now that the last pump kit I purchased only came with one gasket for the pump base - the factory manual shows two gaskets - one on the bottom of the pump base and one between the pump base and the bottom plate. So, I improvised. So much for "form a gasket" stuff. Now making up a proper gasket for the top of the water pump base.

Next steps: get a new thermostat and put everything back together and see how it runs in a barrel.

 

[minuteman62-64]

I'm going to call this one a success and take a short victory lap (at least around the kitchen).

So, re-installed the old, but still functioning, 143 degree thermostat. I had been using the form-a-gasket stuff for the thermostat cover, but decided to cut one from gasket material while I was in gasket making mode.

Replaced the disintegrated form-a-gasket stuff between the pump housing and the base plate with a hand made gasket. Also replaced the gasket between the pump housing and base plate with a hand made gasket thick enough so the gasket mates before metal-to-metal contact between the impeller cartridge and base plate. Finally, switched to the OEM pump housing and impeller cartridge I had on hand and installed a new OEM impeller.

Ran it today in a barrel. Ran about 20 degrees cooler at all rpm's than before (duh - replaced 160 degree thermostat with 143 degree one). Stream from tell-tale, even at idle, was unbroken. Previously stream at low rpm's kind of sputtered out. Tell-tale stream shot out about 4 feet at 1500 rpm - better than before. Finally, temperature, as measured by my cylinder head temp gauge, was steady at 143 degrees at all rpms.

Since the water pump feeds the tell-tale before the thermostat, I'm pretty sure the improvements to the water pump helped quite a bit with the flow from the tell-tale . Of course having a thermostat designed to keep the engine about 20 degrees cooler is also a big factor.

Well, I guess the old Mariner isn't quite ready to head for Mexico yet. Next, time for a Bay run.

 

[Texasmark]

Super! You did good "Mr. Mechanic!" On the T stat, the 90 hp in my avatar is a 2002 and I bought it in 2004 used. First time out (maiden voyage) I had temp problems at low speed. In short, it was the T stat. Big guns on here, especially those operating in salt water recommended frequent stat changes, some as often as annually. Years ago, before the days of sensors and alarms, I had a 70 hp Rude and in short, a stuck stuck stat cost me a power head overhaul, $1k machine work and parts...my labor otherwise. Nasty little (sometimes necessary) suckers!