'93 evinrude 70 stumping mechanic

[df12051]

i have a '93 70 horse that is now in the shop of the 3rd time in a month. History - the engine sat up for about 18 months due to illness. Fuel had been sabalized with Sea Faom before storage but nothing else done. I pulled it home from stoarage - charged he battery - sprayed wd -40 into each cylinder and then hand turned the engine over and let it sit overnight. Started right up the next day on muffs. took it to the mech to tune up and tank test to make sure the high speed jets were clear. Got it back and it ran well on muffs with a good tale tale.

Took it to the lake and ran it at 3/4 throttle for 10 minuted max and overheat alarm went off and tell tale started throwing steam not water. Over heat alarm never went off but tell tale picked up intermittently. Limped back to launch and took boat back to mech. He was able to duplicate problem in the tank after a bunch of running. Compression was within 10 % across all 3 clyinders. He replaced impeller and housing, thermostat and added scopes to the water pick up and tank tested. He also repalced heat alarm as it tested defective. He also changed the tell tale tap to the top of the head per envinrude service bulletin from 1994. All ran well.

Chapter 2 - picked up boat and took to water. Launched and within 10 minutes at 3/4 throttle heat alarm back on and steam coming from tell tale. Went to idle back to launch and tell tale picked up and alarm went off. Was afraid to rum it but came back to launch with tell tale working at 3/4 throttle say 4000 rpms. took it back to shop and the mech is baffled as to what to look at next.

Any advice?

Thanks

 

[clanton]

Re: '93 evinrude 70 stumping mechanic

The temp sensor pig tail wire color should be tan/blue stripe.
OEM waterpump kit had different impeller, thermostat cover, and water pressure spring.
Motor mounted too high?
Anything mounted on transom close to motor? Should be at least 12 inches from side of gearcase.

 

[jtexas]

Re: '93 evinrude 70 stumping mechanic

Clanton, are you thinking maybe the mechanic installed the wrong parts?

df, I'm wondering...when the mechanic said the temp alarm "tested defective" was he referring to the temp switch, or the horn, or what? Was it giving you a false alarm? Does that mean he thinks the motor is *not* overheating? Then why did he replace all those cooling parts? Did the thermostat test bad also?

Why do you need modifications to your water pickup? What kind of boat is it?

Here's a few other reasons why motors overheat (apart from faulty water pump/thermostat/poppet valves):
* inadequate oiling.
* lean burn (too much air not enough fuel).
* bad timing.

Hard for us to comment, since you didn't do the work yourself.

 

[df12051]

Re: '93 evinrude 70 stumping mechanic

Thanks guys,

Here is some infor you asked for.

Nothing is near the water pick up that hasn't b een there for 12 years when the engine worked properly. The boat is a 17 ft Mako Center console.

The mechanic replaced the temp sensor that sends the over heat alarm to the horn. He did this as once the engine overheated it did not go turn off unless the key was turned off - even the next day with a dead cold engine. He was able to recreate the tell tale putting out steam (not water) and the overheat alarm going off. That is why he changed the impeller and its housong as well as the thermostat. After this fix the problem continued except that when the tall tale was putting out water (not steam) the over heat alarm would turn off.

That is why this is mystery. No water in the cylinders so the engine is not circulating and then does.

any other thoughts?

Thanks

 

[bktheking]

Re: '93 evinrude 70 stumping mechanic

Could be a bad pump, i'm surprised he hasn't pulled it apart to inspect to see if there is damage to the new one. How was the old impeller, was it whole?

 

[df12051]

Re: '93 evinrude 70 stumping mechanic

Old impeller was in great shape - had not taken a "bad set" while in storage. He replaced the impeller plus housing to ensure a good one was in there.

 

[trendsetter240]

Re: '93 evinrude 70 stumping mechanic

Does the motor still have the VRO hooked up? It may not be getting enough oil. Could try mixing 50:1 in a portable tank and running off that to see if the problem still happens.

My first thought though would be a partially blocked cooling passage. As a long shot you could take a garden hose and spray water into the tell tale to try and clear out any blockage. Use your thumb over the end to make a higher pressure spray.

Could be insects crawled up in there and mad a nest or something that's now reducing the water flow.

 

[df12051]

Re: '93 evinrude 70 stumping mechanic

VRO2 disconnected years ago and run a premix of 50 to 1 with Seafoam in every tank. the problem started with the old impeller (which was in good condition without any set when removed) and continues with new impeller and housing. This leads to it not being an impeller problem or thermostat problem as it was also replaced the first time this problem came up. I thought of the insect nest as well but the engine runs without overheating on the muffs and puts out a great stream of water. If the internal water passages had a nest then that stream would be blocked as well. the mech added scopes to the water intake as well.

the problem only happens at RPM's that open the high speed jets it seems.

Any other thoughts or wisdom would be much appreciated.

 

[coolguy147]

Re: '93 evinrude 70 stumping mechanic

clean and rebuild carbs all the way. replace fuel lines to prevent future problems.

you never checked compression? possibly overheating from to much of a carbon build up.

the right spark plugs?

key in driveshaft? for the impeller?

what are scopes?

 

[clanton]

Re: '93 evinrude 70 stumping mechanic

Running on the muffs, no load, does not make as much heat as running in water pushing the boat.

This is what I would do if I was working on the motor.

Visual inspection of engine, for missing parts, incorrect parts, broken parts, and more.
Remove gearcase inspect waterpump, watertube, water pickup screen, replace with OEM kit. OEM kit contains the latest changes.
Remove the thermostat, connect waterhose to watertube, back flush engine. Should have good water flow.

Install gearcase, engine in water , start engine, at 2000 rpms water flow should be gushing out of thermostat housing. Install correct thermostat and related parts.

Water test, Still running hot, remove cylinder head for inspection.

 

[clanton]

Re: '93 evinrude 70 stumping mechanic

Exhaust seal in place on gearcase?

 

[cougar1985]

Re: '93 evinrude 70 stumping mechanic

ive ran into a few motors that had similar problems .no matter wether i changed pump housing or impeller it would not circulate properly.the trick i found is to coat the two mating surfaces of the pump housing with avaition sealer and assemble .problem solved ,3 differnt times!my own humble theory is the surfaces get slightly pitted or warped and will not seal properly whether you have a new housing doesnt make a diff either.i might add that i had a 33 hp that drove me wacko changing impellers ,housings etc till i tried the sealer and presto no more cooling problems.could be that one of the surfaces is slightly out for what ever reason but the sealer cured it for me on more than one occasion.i use it all the time now.

 

[jtexas]

Re: '93 evinrude 70 stumping mechanic

....

...

Why do you need modifications to your water pickup? What kind of boat is it?

Here's a few other reasons why motors overheat (apart from faulty water pump/thermostat/poppet valves):
* inadequate oiling.
* lean burn (too much air not enough fuel).
* bad timing.
...