Evinrude 88 HP (1987) cooling question. 88 special

[sledman11]

I have been working on a friends outboard (88 special). It had a leak between the thermostat housing and the exhaust plate. I could not tell where it was coming from so I replaced both the two gaskets on the exhaust plate and install a new thermostat kit. Before I did the work I was running it on a hose. It seemed that the heads/cylinders were hotter than they should be. I don't have the tool to measure the actual temperature. I probably will hit harbor freight and pick up an infrared thermometer, One would burn your hand on the cylinders if you touched it for more than a second or 2. I was hoping that installing the thermostat kit would take care of that. Even with the new thermostat kit installed the motor seems hot to me. I have read some great threads on the cooling of this motor. I am still a bit confused on a couple of things. How does the hot water from the motor get down to the thermostats with the thermostats and poppets closed? There is a lot of spring tension on the poppets. What makes them open? What are the poppets for? I ran the motor with the two hoses that go to the thermostat housing disconnected. I had good flow and the heads/cylinders stayed cool. Thanks for all the great information that I was able to pull out of other threads. It is certainly a great resource for us DIY'ers.

 

[emdsapmgr]

Your V4 thermostat housing performs two cooling functions. 1. At idle all the cooling water goes through the stats. Pressure relief vavles closed. The thing is that to get the warm water to the back of the stats to cause them to open, warm/heated water must go through the small hole(s) in the plastic vavle body sandwiched in the stat housing. If (depending on year) the single oval hole (newer) or the dual pinholes (older) every plug up, not warm water will get to the back of the stat to cause them to open. So, when overhauling, make sure these hole(s) are OPEN or it will overheat at idle. 2. Once the boat gets on plane, the force of the lower through the water will force extra pressure/volume of water up into the stat housing. This extra pressure will cause both nylon pressure relief valves to open. This extra volume of water will actually reduce the temp of the powerhead as long at you are on plane. Maybe 20 degrees from normal idle temps. All normal. The stats open at 143 degrees, so normal idle temps will vary between 143 and 154. Normal. Once on plane, the temp gauge may go down to 123-133. In the spring on a cold lake, the temps may not even register on the gauge when planning, due to the cold water. You will get an overheat at around 212 and the hot horn will silence once the powerhead gets back to 175-still way to hot for normal operation.

 

[sledman11]

Thanks for the very quick reply. A ton of great information on how the coolant system works on this engine. Not sure what you are referring to as the "plastic valve body". Are you referring to the pressure relief valves? Hate the thought of taking the thermostat housing apart again but sounds like I need to make sure those holes that let the hot water reach the back side of the stats are clear. Just need your help in understanding where these holes are located. Thanks again.

 

[sledman11]

Took at look at the exploded view of the thermostat housing. Are the holes located in the spacer that the thermostats sit against? Part #

0321693

VALVE BODY

 

[interalian]

Yes, the assembly goes, from outside to in: casting with hose fittings to cylinder head, gasket, plastic spacer (with bleed holes and locating points for thermostats and poppets), gasket, powerhead/exhaust adapter plate.

Coolant flow:

 

[sledman11]

Great diagram. Can I tell if the thermostats are open by the flow of water coming out of the lower unit at some port? Port side heads gets up to 175 degrees after sitting at idle for a while. Starboard side around 155 degrees. Thermostat housing is coming off.

 

[interalian]

Yeah, that's too hot. Might not be bad thermostats, might be blocked bleed holes. Or swolen diverters in the block.

 

[emdsapmgr]

The part number referenced above is the valve body with the holes in it. You can see the smaller holes in question between the 4 large holes. Those need to be open. Yu can also imagine that it's not too hard for the small hole to get plugged up with debris/sand, etc over time.

 

[sledman11]

Thermostats are new but I did not check the bleed hole(s) when I had it apart. It ran very cool when I had the hoses disconnected from the thermostat housing. Could the diverters still be bad if it runs very cool with these hoses disconnected? Can anything get plugged after the thermostats? Down in the mid and lower units. Ended up going water-skiing last night so did not get the thermostat housing off to check the bleed holes.

 

[sledman11]

No Title

Just took a moment to look at the diagram for the thermostat housing. To me it looks like they show the gasket for the thermostat (#93) in the wrong location. I am pretty sure mine were under the thermostats. Between the thermostat flange and the valve body (#91).

 

[interalian]

The casting where the thermostats mount doesn't have a full circle of support, so it would make more sense for gasket 93 to sit between the thermostat and the spacer 91. I've seen the drawings both ways.

 

[sledman11]

Just wanted to follow up with you guys to let you know that clearing the bleed hole in the valve body took care of my over heating issue. Cleared it out with a drill bit and re-assembled the thermostat housing. Thermostats now open up as they should and the heads measure 135 degrees on one side and 120 on the other side. Thanks for your help on this. Hopefully this thread will help others out in the future.