Evinrude 70 HP overheating

[BoatAddicti0n]

I just got a boat powerded with 1989 Evinrude 70HP VRO, 3 cylinders.

Checked compression (OK), replaced sparkplugs and impeller (the pump works with great presure) but the temperature seems quite high (the water comes out warm and when I touch the cylinders, I can only hold for about 7 seconds before it burns my fingers). I did not hear any alarm and did only run it in idle, shutting if off, as I assume the temperature shuold be so that I one could hold the cylinders for long time in this condition.

I have seem quite some threads about tech bulletins on OMC cooling system for this model/year...

QUSTION 1:
I would start replacing thermostat. Is this correct?

QUESTION 2:
Should I also replace temperature switch?

QUESTION 3:
Is it madatory the relocation of the tell-tale hose?

NOTE I drop these questions while I wait the OMC repair manual to reach my residence in Sweden.

Thanks for any input!

 

[ezeke]

Re: Evinrude 70 HP overheating

You should be able to hold your fingers on the cylinder head for the three count; any more and you risk third degree burns. The head should be in the 140 degree range when the engine is running - that's too warm to keep finger contact for longer than a three count without risk of injury.

Temperature switches rarely go bad, but check the circuit to be sure that the wiring is good and that the warning horn is good.

The relocation of the tell-tale hose was to prevent air from entering the cooling circuit. If you don't do the change, re-route a longer hose to the top of the engine and back down to the outflow connection.

 

[BoatAddicti0n]

Re: Evinrude 70 HP overheating

Thanks for the super.fast response!
I have fixed my problem just by cleaning termostat.

During my adventure, I have gathered/EDITED material from other posts, which I reproduce here:

The water pump will provide cool water to the powerhead. If you have a good impeller(water pump), the tell-tale(pisser) should be working as soon as the block starts to fill with water, regardless of the condition of the thermostats.

A working impeller does not mean that your engine is properly being cooled. In order to be properly cooled, the powerhead needs to have water circulating around the cylinders water jacket.

The thermostat opens and allow water to circulate around the cylinders jackets. The goal is to maintain temperatures less than 163 F. The thermostat partially opens around 135 to 140 F, and is fully open around 160 F. This will take effect in idle or on plane. However, while on plane, the pressure relief valves in the thermostat housing will open, flooding the powerhead with extra cooling water, rergadeless of the temperature. There is a small hole (or pair of holes) in the thermostat valve body. make sure these twin pin holes (or single oval hole-depending on year) are open and not plugged. If this/these holes plug, you will get an overheat at idle.

Temperature switch goes closed at 180F (83*C), and will stay closed until a drop in temp (switch closed = sound alarm ON).

Things that can cause an powerhead to overheat even though you have a good stream of water coming out of the tell tale, the exhaust relief hole:
0. Trapped air in the cooling system, avoinding water to circulate in the upper parts of the cavity (3 cylinders 60/70HP)
1. Stuck or obstructed Thermostat from salts, to junk, gunk and sand. Just bad T-stat
2. Obstructed passage to the cylinder heads caused by foreign material (bits of an old impeller), salts, and sand. (Obstructed water tube near power head or distorted water tube gromet)
3. Sand, salts or foreign material occluding the water jackets prevent water from circulating around cylinders.( This happened to me and I removed the the cylinder head and cleaned out the passage ways and a new T-stat. My Evinrude 6hp was back in business)
4. Swollen water deflectors in larger motors and can be caused by an overheating situation. (these are never mentioned in service manuals)
5. Blown head gasket between cylinders that allows heated compressed air in the water jacket systems and prevent water from circulating.
6. Lean carburetor adjustment and not enough lubrication to inside the cylinders, pistons and rings.

If your engine is primarily used around salt water or sandy environments then chances are that statements 1, 2, or 3 are a high possibility. (So flush your motor well after a salt water run with fresh water)

If the motor is used but new to you, any of the situations could apply.

There were a number of service bulletins about overheating that concerned Johnson/Evinrude 60 HP and 70 HP. IF your engine does not have the water tell-tale (pisser) fitting on the top of the block, check the bulletins about relocating the fitting from the port side of the motor to the top of the block to help in bleeding off trapped air in the cooling system (OR "re-route a longer hose to the top of the engine and back down to the outflow connection").