Intermittent Overheating?

[minuteman62-64]

1982 Mariner 30 HP. Last three times out had short term overheating episodes.

First time ran about 10 minutes at 3/4 throttle, then coming back into the "no wake" zone the cylinder head temp went up into the 200-220 degree range. Slowed to idle, temperature dropped and made the remainder of the run (maybe 1 hr.) at lower speeds w/no further problems.

Second time at idle at the dock right after launch. Same thing. Temp began rising to the 200-200 degree range. Cut the motor, completed post launch prep, started up and ran for about 2 hours at various speeds, including a short streach at 3/4 throttle w/no further overheating.

Today ran for about 90 minutes at low speed to maybe 1/2 throttle w/ no problems. Ran it up to maybe 2/3 throttle and the overheating began again. Slowed to low speed and then cut the motor for about 2 minutes. Started it up again and had no problems the rest of run (another 30 minutes or so).

Good flow from the tell-tale all the time, even when the temperature was rising.

Impeller is a little over a year old with only about 15 hours on it.

Any ideas where to look for the problem?

 

[aussieflash]

Re: Intermittent Overheating?

Could be the gauge playing up.Check cyl head with heat gun.Is telltale water hot?
If equipped check Tstats and poppet.

 

[minuteman62-64]

Re: Intermittent Overheating?

According to my HF heat gun the gauge is good.

I was at the launch ramp this a.m. and saw a motor identical to mine - but the flow from the tell-tale at idle was better than the flow from mine at cruising speed. So, since I had an episode where the motor was running with the water intake above the surface (due to my ignorance) I'm going ahead and replace the impeller. Then I can look at other issues and eliminate the impeller as a source.

 

[Bosunsmate]

Re: Intermittent Overheating?

While you are at it you could take off the thermostat cover and see if anythings clogging up behind the thermostat/ poppet. Try the thermostat for correct opening in a stovepot

 

[Texasmark]

Re: Intermittent Overheating?

While you are at it you could take off the thermostat cover and see if anythings clogging up behind the thermostat/ poppet. Try the thermostat for correct opening in a stovepot

Ditto.

 

[minuteman62-64]

Re: Intermittent Overheating?

I pulled the lower unit and took the water pump apart today. The impeller seemed OK except that two of the arms had a different set than the remaining arms (the two looked like they had been rotating counter-clockwise and the remainder looked like they had been rotating clockwise). That doesn't seem right.

Anyways, new impeller on order from iboats. While I'm waiting I'm going to pull the thermostat and test it and also run a water stream through all accessable water passages.

While I have it apart I decided to replace the drive shaft seals and the shifter boot (all original 1982 parts). I ordered the seals, an "O" ring the boot and some gaskets from Crowley - I'll have to wait for this stuff also to arrive before I can reassemble the motor.

As an aside, I had purchased a slide hammer to use in replacing the prop seals - using the technique of drilling holes for sheet metal screws and using a vice-grip attachment to pull the seals out. That hammer, together with the vice-grip attachment, paid for itself today. The Service Manual technique of using a couple of screw drivers to pry the water pump base out was going no where. I was able to slip one of the puller arms under the base, grab it with vice grips mounted in the slide hammer and easily tap it out.