Evinrude 8hp super hot 1984

[archcycle]

E8RCRM 1984 8hp

I got this motor running recently and all seemed good until I checked the head temperature and found 280*. It's running in a 5 gallon bucket and it has a strong telltale stream.

Removed a thoroughly dead and rotted thermostat and started it up and water gushed out of the housing so I replaced the cover and it heated right up again and after about a minute it was back to 240+. The water pump is definitely moving water.

I pulled the exhaust cover and the head and inspected all of the water passages from the water tube to the escape at the bottom of the head. No obstructions. Replaced all of the gaskets with new ones.

It fired right up and ran way better than before which I had thought was pretty good to begin with (that old head gasket was pretty well cooked) but after a minute or two it started heating up so i bumped the RPMs up to see if I could coax some more water through but the temp just shot back up and I killed it at 200*.

Someone told me that when super lean these motors run smooth but heat up really fast. I'm missing the cover for the air box. I didn't bother trying to tune it after putting it back together since it fired up quickly and ran smooth.

Opinions on A/F being my issue or is there something else? The only other thing that comes to mind would be bubbles from the exhaust interfering with the water intake but I know it's pulling water because it gushed out of the thermostat hole when that was open and it is peeing.

 

[twocyclemania]

Re: Evinrude 8hp super hot 1984

Are you sure it's running as hot as you describe? Is the thermometer giving you an accurate read? At that temperature you would probably be seeing steam come out the exhaust and probably the motor would run erratically if at all. I have the same motor and my thermostat seized while running. It was so hot that the plastic piece that holds the throttle linkage (where it's mounted to the head) melted. Pulled the thermostat, used a zip tie for the linking and went on my way. When it happened there was visible smoke; I thought it was on fire. If you have water pumping through the head (with the thermostat removed) I'm wondering if it's really overheating. Sorry but after reading all you've done I can't think of anything else.

 

[nwcove]

Re: Evinrude 8hp super hot 1984

im with tcm....at those temps it should have been blowing steam and probably would have stalled. missing the cover for the airbox wont have any effect other than more noise.

 

[archcycle]

Re: Evinrude 8hp super hot 1984

I'm using an IR pyrometer that definitely works. Taking readings from the head right above the spark plugs. I wouldn't expect low 200s to melt the nearby plastics in the short time I've had it running in this controlled setting. It did instantly boil water that touched the head so I can say with certainty that some points of it reached at very least 212*

The only thing I can point to right now is some guy whose credentials I can't vouch for who said these small 80s OMCs can do that just from being set too lean.

edit: hopefully i'll get a chance to test it out richer this evening or tomorrow. unless i decided to wake up the neighbors tonight. it wouldn't be the first time.

 

[boobie]

Re: Evinrude 8hp super hot 1984

Put it in a big garbage can and see what happens. The water has to come up over to half the exhaust housing length.

 

[Will Bark]

Re: Evinrude 8hp super hot 1984

Agree with Boobie; that water could be getting awfully hot in a 5 gallon bucket, put in a big garbage can and give it a try. Good luck.

 

[Vic.S]

Re: Evinrude 8hp super hot 1984

I think you will find that the cylinder head does get pretty hot around the spark plugs. Anywhere else should not be so hot that you cannot touch it and maintain finger contact briefly
A symptom of overheating is steam issuing from the exhaust back pressure relief ports on the leg.

Have you renewed the pump impeller?

 

[archcycle]

Re: Evinrude 8hp super hot 1984



I bought a big tub to make sure it had space to blow its bubbles and to get water pressure from deep immersion. The telltale started up immediately, hose on high keeping the water very cold.

Perhaps the impeller is moving enough water to hit the telltale which is one of the first things the water would encounter after reaching the top of the water tube but doesn't have enough pressure to force through the closed system when the thermostat cover is off? That doesn't really mesh up well with the fact that it did move a good amount of water out of the thermostat housing with the cover off, but other possibilities are slim at this point.

It sure does run well though..

A new impeller certainly never harmed anything so I'll do that now.

 

[raczekp1]

Re: Evinrude 8hp super hot 1984

new termostat wll not harm motor also

 

[the machinist]

Re: Evinrude 8hp super hot 1984

From the attached photo, it appears that you are not running the motor in gear in that small a barrel. On that motor the intake is a screened tube imbedded into the portion of the fin BEHIND the prop, if the holes in the screen are partly plugged with debris, you may not get enough water flow into the motor UNLESS the motor is in forward gear pushing water into the screened intake.

 

[Vic.S]

Re: Evinrude 8hp super hot 1984

Difficult to be sure but the water stream from the telltale does not look all that strong in your picture. At anything above idle it should be a powerful jet of water.

While you are changing the water pump impeller connect a hose to the water tube and make sure you can get a good water flow through the engine.

The grommet at the top of the water tube on these can be a PITA . Corrosion round it can squeeze it over the top of the tube until it blocks off the water flow.

If you poke a stout wire up the water tube and hit something solid at the top all is well but if you hit something that feels rubbery that is the grommet obstructing the top of the tube!

This picture shows what I mean. (Not in fact mine but this is the single most troublesome thing on my 1984 Yachtwin)

This picture ( which is mine) shows a normal flow from the telltale

 

[archcycle]

Re: Evinrude 8hp super hot 1984

I had to put this aside for a while but am back on it again.

It was in N, not in F, so maybe that was my cooling problem, but after it sat in the bucket for a while it leaked out a lot of water/emulsified gearcase oil mix so I dumped out the gearcase and it was full of water so now I'm also replacing the seals in there. The impeller was in pretty sad shape.

But how do I get the seals out of the gearcase head? I made a tiny puller and got the bushing out of the back of it pretty easily and was expecting it to hold the seals in place but it doesn't look like that is the case.



The machinist your rambling on the fuel pump was very helpful well done.

 

[Vic.S]

Re: Evinrude 8hp super hot 1984

.

But how do I get the seals out of the gearcase head? I made a tiny puller and got the bushing out of the back of it pretty easily and was expecting it to hold the seals in place but it doesn't look like that is the case.

I've replaced mine a couple of times.

I did not remove any bush. I simply knocked the old seals out and pressed in new ones.

With the bush out it should be easier to knock the seals out. Be careful with that bush though... AFAIK its not a separately listed part

First time they came out easily but I did wreck them ( or at least one of them) getting them out the second time.... that was annoying because I then had difficulty obtaining new ones.

 

[archcycle]

Re: Evinrude 8hp super hot 1984

I simply knocked the old seals out and pressed in new ones.

I just don't see how they come out. Here's a shot from the forward facing end. Do I just knock them out through these holes? Is the cap on the aft facing end actually the outer seal or something that comes out? I can't really tell as it's a bit corroded on the outside.

 

[racerone]

Re: Evinrude 8hp super hot 1984

The 2 seals pry out from the outside.--------Be very careful as that housing is obsolete.

 

[archcycle]

Re: Evinrude 8hp super hot 1984

edited

 

[archcycle]

Re: Evinrude 8hp super hot 1984

So if this pictre from post 14 is the bow facing end where you can see the seals through two passages




and this is the aft facing end


Is the red marked part the outward face of the water seal or else a cover that bangs out with the seals through the holes in the the bow end, or else pries or pulls off from the aft end?

Sorry if I'm being a bit thick here but I just want to be certain before I start prying at more things

 

[Bosunsmate]

Re: Evinrude 8hp super hot 1984

I think ive read all these posts properly, one thing i kept thinking is that i cant find where you say that you replaced the thermostat?
Have you done that?
On some motors, i dont know if this one is like that, but if you pull the thermostat out you dont get the block and head filling with water properly and itl overheat

 

[racerone]

Re: Evinrude 8hp super hot 1984

I will have a look at one of those housings and a factory service manual to see how they take the seals out.--Patience here.

 

[Vic.S]

Re: Evinrude 8hp super hot 1984

I just don't see how they come out. Here's a shot from the forward facing end. Do I just knock them out through these holes? Is the cap on the aft facing end actually the outer seal or something that comes out? I can't really tell as it's a bit corroded on the outside.

I dont remember any cap and none is shown in the parts list, is it? Look at the new seal. I am pretty sure you will find its all part of it

I think i probably knocked them out through those slots.

10years plus since the last time it did this but it really was a simple straight forward job. Quite unmemorable.

It does not matter how you mutilate the old ones. Just dont damage the housing!