How long does it take to overheat?

[eavega]

I have a new-to-me 1976 70 HP Johnson 70EL76D. easy to start and run, has an electrical issue (Tach does not work unless connected to the yellow wire coming from stator, battery does not charge) which I am assuming is the rectifier (on order from iBoats). My last issue before actually putting it out on the water is temperature.
I ran the motor in a barrel, and to me it felt like the heads were getting warmer than I like. I've dropped the lower to look at the impeller, and it looks to be in fairly good shape; what I would expect after perhaps a year of occasional use (blades were bent in the direction of rotation, but not cracked or obviously worn down, and it still required a little bit of effort to get the pump housing down around it). I also checked the thermostat for proper functionality. This vintage motor has no telltale, and I didn't see huge quantities of water dumping out the exhaust relief ports, just droplets really. The overheat alarm didn't go off, and I could still lay my hand on the cylinder head for a few seconds without it being uncomfortable. I ran in the barrel for probably 5-7 minutes, working through the gearshift, throttling up (below 2000 RPM to be sure), etc before shutting down. I don't have a non-contact thermometer (yet), and was just wondering if the motor was going to overheat due to no water circulation in the jacket, how long would it take while mostly idling in a barrel before it did? I'm worried that something may have gotten up into the water tube while this motor was idle (I did pull a wasps nest out of a space in the lower unit, which if it broke loose when the motor was tested could work its way up into the water tube and clog the whole works, thus not allowing any cooling water to circulate) and I am trying to rule that out without taking the head off. Any thoughts or recommendations would be welcome.

Rgds

 

[boobie]

Re: How long does it take to overheat?

The first thing you should do is disconnect the tan wire on the temp sender in the cyl head ,turn on the key and ground the tan wire from the wiring harness and check the horn to see if it blows. Then get a temp gun and give it a good water test. You won't see much water out of the exhaust reliefs until the mtr is good and warm and the thermo is open. Check your temp at same time with your gun.

 

[eavega]

Re: How long does it take to overheat?

The first thing you should do is disconnect the tan wire on the temp sender in the cyl head ,turn on the key and ground the tan wire from the wiring harness and check the horn to see if it blows.

Sorry, forgot to mention that I did this. Horn is working fine.

The non-contact thermometer is on order.

Thanks

 

[HighTrim]

Re: How long does it take to overheat?

If you can hold you hand on the heads for a 1, 2, 3 count, or you can splash water on the heads without it sizzling, you are usually ok. But as stated, cant hurt to verify the actual temp.

Just so you know, running in a barrel will cause the motor to run warmer than on the open water since you are recirculating the spent cooling water. Each time it cycles through your cooling circuit it gains temp.