Overheating - Was It The Thermostat?

[minuteman62-64]

I've got a 1982 30 HP Mariner. Took a run in San Diego Bay this a.m. All seemed normal. Good flow from tell-tale. Didn't notice the exact head temperature, but didn't recall it being excessive (normally shows in the 145-150 degree range, again, on my home made head gauge). Shut the motor down to do some fishing, and, a few seconds later my home made overheat alarm went off. Since the motor was shut down, I figured the thermistor had crapped out so I pulled the fuse to shut it off.

Started the motor and began running at low speed to change location. Noticed the head temperature reading was about 180, but, still strong flow from tell-tale. When I speeded up, the temperature began to drop and got back to the 145-150 degree range.

We fished some more, then decided to cruise by the Spanish Landing area, about 1/2 mile down bay. Same thing with the head temperature, except after a few minutes it wouldn't drop even going at a higher speed. Still strong flow through tell-tale.

Limped back to the launch ramp with a run/shut down/run shut down sequence. Got to the dock with head temperature showing about 200. Running OK, no steam or smoke, still good flow from tell-tale, but definitely way too hot. Let it cool for awhile, then pulled the thermostat. Housing was bone dry, and thermostat was wide open.

Buttoned it up w/o thermostat. Head temperature was still showing 140 degrees, but dropped like a rock as soon as the water started pumping with out the thermostat.

Ran OK to put back on trailer and to flush back home.

Any ideas on problem? New thermostat, last I looked, was about $140. Cheap for peace of mind, but, I'd like to make sure I've zero'd in on the problem.

 

[joed]

Bad Impeller. Had the same issue one time. The impeller was hardened. The vanes would not flex tight against the side of the pump housing and it did not pump enough water at low speed. It was fine at high speed.

 

[minuteman62-64]

Bad Impeller. Had the same issue one time. The impeller was hardened. The vanes would not flex tight against the side of the pump housing and it did not pump enough water at low speed. It was fine at high speed.

Pretty sure it's not the impeller. It's only a couple of months old with less than an hour on it. Besides, had strong flow through tell-tale at all rpm's.

 

[minuteman62-64]

Apparently it was not the thermostat. Got a new thermostat (found one for $62). Installed it, and, running on muffs, still overheated - temperature ran up to about 200 F in 5 minutes - usually runs at about 145 F on the muffs.

Did find out one interesting thing. Ordering the new thermostat I looked at the parts diagram and noticed a metal washer that sits on top of the thermostat. Didn't previously have that. What it does is hold the thermostat down so the only water flow occurs when the thermostat opens. Without it, the thermostat gets pushed up and allows some water flow between it and the housing. Here I'd thought I had one of those motors that began flow through the tell-tale right upon startup. Nope. Oh well, live and learn.

Anyways, back to the drawing board on the overheating. Next step, drop the LU, check the impeller and blow water through all available orifices. If nothing shows up there I'll be back asking for more advice.

 

[Texasmark]

Follow your tell tale hose back to the engine block. Lot of them come off the exhaust manifold plate on the port side of the engine. That cooling loop isn't controlled by the tstat so it gets fresh water constantly.

For the stat to work as designed you need it to seal off the flow of water till time to open. If that takes the washer then so be it. The pellet on the stat is normally stamped with the opening temp (143F) and as the temp increases from that, during the next 10-15 degrees the stat will continue to open till full open. The OT alarm is 195F on some engines, maybe all.

Confusing comment about the washer and effects you mentioned. If the stat isn't properly seated you'll have water flowing around it meaning you are getting cooling flow. When the stat opens you will get more unless by the stat being unseated it's blocking the exit point from the stat housing area for the cooling water and that would make sense. Nothing else you said solicits an answer...confusing to me.

 

[minuteman62-64]

Follow your tell tale hose back to the engine block. Lot of them come off the exhaust manifold plate on the port side of the engine. That cooling loop isn't controlled by the tstat so it gets fresh water constantly.

For the stat to work as designed you need it to seal off the flow of water till time to open. If that takes the washer then so be it. The pellet on the stat is normally stamped with the opening temp (143F) and as the temp increases from that, during the next 10-15 degrees the stat will continue to open till full open. The OT alarm is 195F on some engines, maybe all.

Confusing comment about the washer and effects you mentioned. If the stat isn't properly seated you'll have water flowing around it meaning you are getting cooling flow. When the stat opens you will get more unless by the stat being unseated it's blocking the exit point from the stat housing area for the cooling water and that would make sense. Nothing else you said solicits an answer...confusing to me.

On this motor the tell-tale is fed via internal passages in the block - no hose.

The washer is (probably?) not relevant to the current overheating issue. Motor ran fine for the past few years without it. Then the current overheating occurred, also without it. Now it still overheats with the washer in place. The main significance of the washer at this time is in my understanding of the cooling water flow path through the motor. I had previously "figured out" the flow path by squirting water up the water supply tube - thinking the thermostat was closed. Now it looks like the water was actually flowing through the thermostat housing at that time - giving me an incorrect picture.

Anyways, thinking about the problem some more, the overheating was not the spiking that I've had from kelp over the intake. It is a gradual rise and keeps rising even though the pump is putting out enough flow to have a good stream through the tell-tale. I'm thinking I may have a clog in either the circuit through the exhaust housing or the one through the cylinder head, but probably not both.

Next step, check the pump and do some more water squirting (this time knowing how the thermostat is operating). After that, I may be back with questions about some disassembly

Fortunately I get as much enjoyment out of tinkering with my boat/motor as I do actually using it

 

[Texasmark]

Let us hear of any news

 

[minuteman62-64]

Pulled the LU today and did some water squirting tests. I use a hose nozzle with screw-on adaptors that take different sizes of vinyl tubing. Probably working with 30-40 psi.

Appears all the passages are open. With thermostat closed, squirted water up the supply tube. A little stream came out the exhaust opening on the drive shaft housing and a lot of water came out through the opening in the rear of the inside of the drive shaft housing (also got a good stream out the tell-tale - guess it works regardless of thermostat status).

Then, pulled the thermostat and squirted water down the outlet port of the thermostat housing (which puts it directly into the water jacket on the cylinder head). Again, flows coming out tell-tale, exhaust port and opening inside the drive shaft housing.

I did find some soft, mushy salt residue in the container I used to catch the outflow from the motor. Same stuff I've found in the thermostat housing since I started using Salt-Away type stuff as a final, after run, rinse. I wonder if I knocked some old encrusted salt loose inside the cooli

Unless anybody tells me I'm interpreting anything incorrectly, I'm going to move on to the LU and look for, yet another, water pump/impeller issue. If it turns out to be another screwed up impeller I'm giving up on the Sierra stuff and going back to the OEM stuff, hang the cost.

If everything checks out, I'll re-assemble and fire it up again. This time I'll do it in a barrel to avoid any flow issues because of the muffs.

Most of you guys have way more experience with this stuff than I do - so, let me know if any thoughts/ideas.

 

[Texasmark]

Pulled the LU today and did some water squirting tests. I use a hose nozzle with screw-on adaptors that take different sizes of vinyl tubing. Probably working with 30-40 psi.

Appears all the passages are open. With thermostat closed, squirted water up the supply tube. A little stream came out the exhaust opening on the drive shaft housing and a lot of water came out through the opening in the rear of the inside of the drive shaft housing (also got a good stream out the tell-tale - guess it works regardless of thermostat status).

Then, pulled the thermostat and squirted water down the outlet port of the thermostat housing (which puts it directly into the water jacket on the cylinder head). Again, flows coming out tell-tale, exhaust port and opening inside the drive shaft housing.

I did find some soft, mushy salt residue in the container I used to catch the outflow from the motor. Same stuff I've found in the thermostat housing since I started using Salt-Away type stuff as a final, after run, rinse. I wonder if I knocked some old encrusted salt loose inside the cooli

Unless anybody tells me I'm interpreting anything incorrectly, I'm going to move on to the LU and look for, yet another, water pump/impeller issue. If it turns out to be another screwed up impeller I'm giving up on the Sierra stuff and going back to the OEM stuff, hang the cost.

If everything checks out, I'll re-assemble and fire it up again. This time I'll do it in a barrel to avoid any flow issues because of the muffs.

Most of you guys have way more experience with this stuff than I do - so, let me know if any thoughts/ideas.

Watch the water temp in the barrel as it warms up if not overflowing with replacement water due to engine exhaust.

Ensure that the water level in the barrel stays well above the water pump....mid way up the mid section is a good reliable level.

Funny things happen when you barrel run and have it in gear so be careful what kind of conclusion you make with the barrel test.

 

[minuteman62-64]

Ran it in a barrel today. Good flow from tell-tale. Ran at about 160 F at 1200 rpm and about 180 F at idle (650 rpm). This based on my cylinder head temperature gauge which I tried to mount on the hottest part of the head. Looking back over my maintenance charts, seems consistent with past temperature readings (don't have ambient temperature info for time of previous readings - having a heat wave so air temp and temp of barrel supply water was warm today).

Tell-tale stream was warm. Thermostat housing, head and exhaust jacket were hot to touch, but not so hot I couldn't put a finger on.

I'm going to run it again this pm and shoot some readings with my HF remote sensing temperature gun.

Also had one glitch. Had flow going into barrel to provide make-up water - from hose in back yard. Wife saw some runoff and thought water was being wasted, so turned hose off. Result, impeller ran dry for a few minutes. Just as a precaution I'll replace impeller before an on-water run (and, for next test run, switch water supply for barrel to hose right next to boat).

So, I don't know where I am. Seems to be running as before. But, I don't know if I've actually fixed anything. I'd sure feel more confident if I'd found a shredded impeller or a dead mouse in the thermostat housing or anything where I could say "ah, that's the problem!"

 

[Texasmark]

Hear you on that. Temps are fine. Can't tell much in a barrel. Good idea on having a look at the impeller anyway. If you got flow out of the powerhead with 30-40# of water pressure with the stat closed, you must have a poppet valve also, like the larger engines have, that unseats when you get up over 2500 rpm to allow more flow through the engine. At higher rpms the impeller only puts out water pressure in the teens psi. so you were well over that.....sounds normal.

On running dry, when I was a kid I had a 1950's 10 hp ScottAttwater OB that I ran I don't know how many times for a few minutes out of the water to ensure it was ready when I went to the water and rented a boat to go fishing. Used that engine for I don't know how many years and never did a thing other than change plugs. Coup de gras was one day I ran across some old railroad pilings at WOT, where a trestle had been, poles cut off below the water level where you couldn't see them and broke my mid section half in two. Only thing that kept it all from falling off the boat was the shifter linkage. After that I tore the engine apart to see how it was made and found about needle bearings.....when I pulled a rod cap and half of them fell out on the floor....no I couldn't find all of them.

 

[minuteman62-64]

Based on parts diagram, pretty sure no poppets - you can see cylinder head at: http://www.marineengine.com/parts/m...01216-thru-411946/crankcase-and-cylinder-head

Well, still no smoking gun. Just to satisfy my curiosity I pan tested the old thermostat today. Full open at 143 degrees F, just like it's supposed to.

Ran again in barrel, this time checking with HF remote sensing temperature gun to verify cylinder head temperature gauge. Tracked almost perfectly.

Still overheating at idle. Cools right down to 140 degree range once above 1000 rpm. However, at 650 rpm idle speed, temperature just keeps drifting up - went past 220 degrees before I increased rpm's and it dropped right down.

Next step, replace the impeller (after short family trip), just in case. Then check again in barrel.

If still a problem, then what? Pull head and exhaust jacket and look for clogged passages?

 

[Texasmark]

Based on parts diagram, pretty sure no poppets - you can see cylinder head at: http://www.*****************/parts/...01216-thru-411946/crankcase-and-cylinder-head


Still overheating at idle. Cools right down to 140 degree range once above 1000 rpm. However, at 650 rpm idle speed, temperature just keeps drifting up - went past 220 degrees before I increased rpm's and it dropped right down.

Next step, replace the impeller (after short family trip), just in case. Then check again in barrel.

If still a problem, then what? Pull head and exhaust jacket and look for clogged passages?

As stated, probably not enough HP to require the added cooling flow that a poppet would provide. How high is the water in your barrel when testing? Answer that question before you tear into the water pump. I may be loosing track of this thread, but have you water tested the engine lately? Before I tore into it I would water test it and take your HF infrared thermometer with you. 650 is the right number for idle rpm.

 

[minuteman62-64]

Water in barrel was about 3" over the cavitation plate - intake deep enough to get good flow from tell tale.

Impellers are cheap. I'm going to replace it just as a precaution - since it was overheated on the water and ran dry when the hose was shut off. I will water test for sure before I even think about pulling power head/cylinder head/other.

Since the current issue is overheating at idle (with a brand new thermostat), kind of drifted away from this topic, I've started a new thread.

 

[minuteman62-64]

OK, maybe problem solved. See: http://forums.iboats.com/forum/engi...861-30-hp-82-mariner-cooling-system-diagnosis