Late 70s Evinrude 15 hp cooling and idle questions

Hi: I recently bought an older, but apparently well maintained Evinrude 15 hp. From the model number I've pegged it at 1978 (approximately - don't have the number handy now though). It was practically given to me, but started hard and didn't pump water well. Compression seemed a little low (about 90 with my tester), but was dead even.

I've done carb, waterpump and ignition work on a similar vintage Merc 9.8, but never on an OMC. Not having the shop manual nor the time this summer to wait for it or to do the work(!), I brought it to a trusted mechanic for a once over, asking him to rebuild the water pump, clean and adjust the carb., etc. While he was doing this, he agreed compression was a little low and replaced head gaskets (?) which he said improved the compression (I haven't re-tested with my tester yet). He said the cylinders and pistons looked great. While in there, he noticed thermostat needed replacing too.

So, it starts easily and runs very well and I have a couple hundred dollars into it.

Can you tell me if the following is normal for this engine:

When I start at low idle, the tell tale just dribbles, but picks up to a nice stream with just a little bump in RPMs above idle.

At a certain point - when I put it up to a little higher RPMs and/or maybe it just gets a little warmer? - a strong mist begins to come out of exhaust port at the top of the leg. This mist is not present when I first start the engine even though the telltale is streaming.

The heads near the spark plugs get pretty warm (hot), but it barely passes the "three second" rule - I can hold my finger on there for a few, but not more than 4-5 seconds. It seems a little hot. The telltale stream seems to vary from cool to luke warm. I have ordered an infrared thermometer to check the temp. of the head, but am wondering if a "touch test" of less than 5 seconds is cause for concern.

Finally: on the port side there is an idle speed adjustment knob. The tiller control does not have a friction knob like my Merc (maybe because the original twist control was replaced with something that an extension attaches to). The twist control won't stay in place for faster trolling. I usually fish by setting the speed on the kicker, holding that speed with the friction adjuster, and steering with an EZ Steer from the front of the boat. This will not work with this particular twist shift. Am I correct in assuming that the port side adjustment knob would be used to increase trolling speed? OR should I be looking for an original twist shift with a friction adjustment? That port side knob doesn't work well - the inner workings seem a little hinky, maybe because they're just worn out.

Thanks for any advice!

Re: Late 70s Evinrude 15 hp cooling and idle questions

Your cooling seems to behave perfectly normal for that engine, but you'll be able to confirm with the infrared thermometer.
The idle adjustment is (usually) not used to set the trolling speed. It is to set the lowest normal idle speed.

Re: Late 70s Evinrude 15 hp cooling and idle questions

tx1961whaler said:

Your cooling seems to behave perfectly normal for that engine, but you'll be able to confirm with the infrared thermometer.
The idle adjustment is (usually) not used to set the trolling speed. It is to set the lowest normal idle speed.

Click to expand...

Thanks - that's what I thought. Do you know if this vintage of engine normally came with a twist grip that had a friction adjuster so it could be set for trolling without holding it?

Thanks again.

Re: Late 70s Evinrude 15 hp cooling and idle questions

I normally call the friction adjustment a "poor mans cruise control".

As stated, the idle adjustment is for just that, adjusting the idle. Ensure it is at around 650 RPM under load in gear.

If you can hold you hand on the head for a 1, 2, 3 count, all should be well. If water sizzles when splashed on the head, that is a sure sign she is too hot. But the infrared thermometer is the best test. That is one of the best tools I added to my collection for troubleshooting outboards.

The mist that suddenly appears from the exhaust relief is from the t stat opening. That is why you do not notice it at start up, the cooling water has not gotten to temp yet for the t stat to open, allowing the mist to exit via the exhaust relief.

Re: Late 70s Evinrude 15 hp cooling and idle questions

Thanks for the advice gentlemen. You've told me what I thought was true about the temp, idle adjustment, water mist (t stat), etc. I'm going to give it a test fishing one of these days!

One last question: is the original grip w/ friction adjustment something I'm likely to find in an outboard boneyard somewhere? Is it one of those parts that is fairly similar from year to year within an 'era'? I'm afraid to think of buying a new one.

Re: Late 70s Evinrude 15 hp cooling and idle questions

Just a quick follow up for posterity:

Got a cheap infrared thermometer. Fired up the engine, high idle for about 10 minutes. Tested with fingers - could hold on there for a 5 second count after which it got fairly uncomfortable, but not scalding. Tested with IR thermometer and it was somewhere between 135 and 140, which I understand is within normal. I'm looking forward to checking my old Merc kicker as I spent last fall taking off the water jackets and cleaning passages, etc. to eliminate a cooling issue (steam coming out of telltale, but only intermittently, mostly it cooled fine). It is pumping perfectly now, and seems much cooler. I wish I'd had the sense to buy the IR thermometer last year, if nothing else to compare with what it is now.

Thanks for advice