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PostPosted: 15 Aug 2016, 20:46 

Joined: 15 Aug 2016, 18:24
Posts: 7
I’ve been lurking the forums for months now, mostly researching how I will modify the next boat I’m saving for that I plan to purchase next year. Until then, I’m stuck with my 1236 with a 1982 15hp Evinrude (model E15RCNC), which can be a challenge for 2 fat guys! Anyways, I’ve been having a ton of trouble out the 15hp Evinrude when out on the water. Here’s what I know about the motor. It was my dad’s and he purchased it new. It sat for about 20 years in a garage until about 2 months ago when I decided to get it going. I took the engine home and with fresh fuel it started on about the 5th pull and sounded good! I decided to do some preventative maintanence and replaced the water pump and housing, new spark plugs, replaced all gas hoses, cleaned/installed carb kit. I purchased new gas tank and line. It seemed to be running great after all preventative maintenance when at home using muffs. At home I can start the thing hot or cold with no problem, and I tested it like crazy this past Friday since I’d had issues on the water the last few outings.

On Saturday morning I went fishing, and like always it started up fine at the boat ramp. After running WOT after about 5 minutes the engine started sputtering, I made it my fishing hole, and the engine shut off, and wouldn’t start up for anything. I removed the spark plugs and the top plug was a little oily and the bottom plug had a little milky residue on it. I cleaned the spark plugs and I was able to start the motor up with a few pulls, but it sure ran rough and barely got me back to the boat ramp. When I got home again the bottom plug had milky residue on it.

After some research online it seems I may have a blown head gasket? I found a compression tester today top cylinder reads 70psi and the bottom reads 60. Would a blow head gasket give me these low compression readings or is that a piston/cylinder issue? I’ve never dove deep into any motors, sticking to mostly somewhat simple repairs and maintenance. What do you guys think?


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PostPosted: 15 Aug 2016, 23:53 
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Joined: 15 May 2010, 00:38
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Location: Central Florida
At this point you need to pull the head and find out. Run the engine at idle on the hose for a while before doing this to get as much lube in and around the crank as possible in case there is water entry into #2.
Tons of different readings can be had on different comp. testers and how fast the rope is pulled, etc. One thing for sure is that your numbers are low enough for me to tell you to pull the head.
If the gasket is indeed blown then you will also need to pull the powerhead and replace the two water tube grommets before running the engine. Gasket blew because it got hot and that will prob be the reason.
Check for cylinder damage, primarily on the exhaust side.
Take a look at the grommets on the water tubes below. This engine had 122 and 118# compression and zero signs of an overheat. The grommets are distended on the outside and will be closed almost completely on the inside, restricting cooling water flow. This engine belongs to me. I buy and sell a bunch of these. Every single 9.9-15hp I purchase gets a new set of these before the engine goes out the door. I want buyers to be satisfied and I stay satisfied this way too.
No, there is no other way around it.......has to be done but not too difficult to do.
There are 6 powerhead mount bolts, three pan mounts inside and at the bottom of the powerhead, couple of wires, shift linkage, remove starter (have a 3/8-16 nut handy to thread onto the starter bolt to keep the assembly together) fuel lines and a choke knob. Thats about it. This is an excellent opportunity to lube the shift linkage, clean the pan of 34 years of grime and check the upper mounts as well. You will need a pair of grommets and a base gasket. You can trim the tops of the grommets slightly after placing them onto the water tubes to keep this from happening again.

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PostPosted: 16 Aug 2016, 21:00 

Joined: 25 Jan 2009, 15:19
Posts: 112
Your low compression could also be mucho carbon in the rings. I have an 85 15hp and it was peeing decent and not running hot but I read leeroy's ramblings and decided to check the water tube grommets. Thank god I did. They both looked like little sphincters. Would have overheated on me and sure enough burnt an engine.


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PostPosted: 17 Aug 2016, 17:01 
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This is typically what is found when inspecting the grommets for damage.

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PostPosted: 17 Aug 2016, 17:22 

Joined: 25 Jan 2009, 15:19
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Yep mine were that bad. Can believe it was not overheating.


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PostPosted: 17 Aug 2016, 18:57 
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timsmcm wrote:
Yep mine were that bad. Can believe it was not overheating.


How would you know. On that engine there is no hot horn. The only way to tell it is hot is when the engine seizes or you get lucky and blow a head gasket which doesn't happen often on that engine. You could be running very close to that point and never know it.
The overboard indicator is not a "Okay, boss, we're good to go here" indicator. It simply indicates the water pump is pumping something (volume wise)...not that there is sufficient pressure and volume to support adequate cooling at WOT.

NO overboard indicator indicates there is sufficient cooling water available to cool the engine at WOT.


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PostPosted: 17 Aug 2016, 23:55 

Joined: 25 Jan 2009, 15:19
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I carry a ir temp gun and would test it a intervals when I first got the motor. It always was at around 146 to 154 degrees on the block right behind the head. Cool enough for me.


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PostPosted: 18 Aug 2016, 00:08 
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I checked my 1992 15hp the other day after running around for a good bit at WOT at 6900 rpms and my head and top of the block behind the head were right at 145 deg according to my IR gun. For whatever reason, the intake covers were around 180 degrees which I wasn't expecting. Not really much of a contribution to the thread but thought I'd throw it out.



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PostPosted: 18 Aug 2016, 08:22 
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wmk0002 wrote:
... running around for a good bit at WOT at 6900 rpms ...

6,900 RPMs? Is that a typo???????????



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PostPosted: 18 Aug 2016, 09:09 
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DaleH wrote:
wmk0002 wrote:
... running around for a good bit at WOT at 6900 rpms ...

6,900 RPMs? Is that a typo???????????


Nope!
These engines will run 7K all day long if necessary.


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PostPosted: 18 Aug 2016, 09:46 

Joined: 25 Jan 2009, 15:19
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What do you use to check rpms on your motors if you don't mind me asking?


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PostPosted: 18 Aug 2016, 09:51 

Joined: 25 Jan 2009, 15:19
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Pappy wrote:
DaleH wrote:
wmk0002 wrote:
... running around for a good bit at WOT at 6900 rpms ...

6,900 RPMs? Is that a typo???????????


Nope!
These engines will run 7K all day long if necessary.


I think these little 15hp omc motors are just the greatest little motors. Light weight, good power, easy to fish over, and bullet proof.


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PostPosted: 18 Aug 2016, 11:08 
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timsmcm wrote:
What do you use to check rpms on your motors if you don't mind me asking?


I have two methods.
The fastest method for me is a "Reed" tachometer. Works like a tuning fork does and is extremely accurate....and extremely expensive.
Second method is a "Tiny Tach"....slower to hook up but accurate as well and cost effective.

On the left is the Tiny Tach and on the right is the reed tachometer. Probably the only reed tachometer you will ever see.

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PostPosted: 18 Aug 2016, 11:54 
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Location: Cullman, Alabama
Pappy wrote:
DaleH wrote:
wmk0002 wrote:
... running around for a good bit at WOT at 6900 rpms ...

6,900 RPMs? Is that a typo???????????


Nope!
These engines will run 7K all day long if necessary.


Yep, the typical WOT range for the 15hp is 5500-6500, however, the late 80's to early 90's (possibly more) are 5500-7000. My factory service manual verifies it. But believe me, I was skeptical....still am a little honestly lol. It doesn't really sound like it is overdoing it at 6900 rpms with my 8" pitch prop, but I may re-prop to get it down a little closer to 6500, as long as it doesn't feel like it lugs out of the hole.



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PostPosted: 18 Aug 2016, 11:59 
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Location: Cullman, Alabama
timsmcm wrote:
What do you use to check rpms on your motors if you don't mind me asking?


The tiny tach Pappy mentions is probably the best inductive tach available. But you can also get a cheaper one off of Amazon made by Hardline. They are the only cheap one that will actually last a significant amount of time I have found.

https://www.amazon.com/Hardline-Products-HR-8061-2-Tachometer-2-Cylinder/dp/B000FOOAXY/ref=sr_1_1?ie=UTF8&qid=1471535899&sr=8-1&keywords=hardline+tach



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