How do you test a Vernatherm?

[Klink]

1990 Evinrude 70hp uses Vernatherm type thermostat 0434137, it is one piece, it can't be disassembled. The original one could be disassembled and I have it. I'm fixing the 70hp for a friend and found that the thermostat was stuck open, the head would not warm up, so I bought the new one piece thermostat 0434137. I also installed a new pump kit. I tested the engine and it warmed up well and idled well in a tank after I set the link & synch. I tested the temperature around the head with an infrared thermometer gun and all was fine.

I took it out for a test yesterday and it started right up and idled perfect, we had about a 1000 yard idle zone to go through, so the engine had a good chance to warm up well. It ran at idle speed perfect, very smooth. Then I sped up to 4500 rpm and it sped up and planed fine. It ran for like 2 minutes and then began to slow down and the alarm went off. I've seen this many times before and figured it was clogged cooling water passages in the heads, as the heads have never been cleaned. I asked my son to check the pee hole water stream and he said it was hot. I let it idle for a few seconds and the alarm turned off. Then I went back to the dock at idle speed.

I got home, and disassembled the head and found that the water passages are spotlessly clean. This engine already has the factory updated pee hole exhaust out the top of the exhaust manifold housing. The only thing I can think of is that the new Vernatherm type thermostat 0434137 is no good. Is there a way to test them? I am going to remove the vernatherm from inside the old thermostat I have and install the thermostat body and see if it runs at high speed that way, basically running without a thermostat, but I do not like to do that because the engine will idle bad when cold.

 

[t2stroke]

The vernitherm can be put in hot water to see if the center pin moves. Be nice to have a temp gun to tell what temp it moves at. Your motor need a good water pump to move the entire thermostat off its seat at higher speeds. The thermostat assy (pictured blows off its seat to cool the motor. The vernitherm controls the temp at slow speeds.
Your motor has a SB that tell you to use pump kit #432955. It consist of a 6 legged impeller (originally 3) and several other upgrades. You mention the higher telltale upgrade. Instruction sheet is included. Your water pump needs to be in good shape.

 

[Klink]

Thanks for the reply. After reading your description of how the thermostat/vernatherm work, I knew it was not the vernatherm that was the problem, since engine idle temperature was fine. Nevertheless I tested it.

Contrary to what I said before, it looks like the new thermostat may be able to be disassembled to take out the vernatherm and test it and see the little pin move, but I needed to make a tool to do it. So, I tested it by boiling the whole thermostat in water and watching a scratch mark on the base of the vernatherm to see if it moved and also blowing air with my mouth through it. I used an infrared thermometer. Like I thought, it is fine.

Regarding the more likely problem "water pump needs to move the entire thermostat off its seat at higher speeds"

It had the 6 legged impeller, and like I said before, the pee hole outlet was moved to the top. I just put in a new complete kit #432955, though it is aftermarket. The water passages are clean, so the only problem I can see is that the thermostat valve seat cup was hammered in and is crushed in one side. I'm ordered those parts and will install them with a press now that I have the cylinder head off. I'm not sure that would cause the problem, however, now that I have the head off this is my opportunity to do it right.

I always have a water pressure gage and temperature on my engines, I wish I had one here, I would know more about what is going on. However, it is not my engine and "the favor" is getting to be work.
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[Klink]

The vernitherm can be put in hot water to see if the center pin moves. Your motor need a good water pump to move the entire thermostat off its seat at higher speeds. The thermostat assy (pictured blows off its seat to cool the motor. The vernitherm controls the temp at slow speeds.

My take of how this thermostat system functions on my engine:

Looking at the new thermostat design, the little holes at the tip of the thermostat is all the water that can get out to cool the cylinder head cover while the engine is cold, basically it looks like those little holes are there just to get the water to touch the vernatherm so it can react/work/adjust to engine water temperature. So the cylinder head cover is not getting much cooling water through those holes and any water it is getting is flowing through and out the exhaust at the bottom. As the engine temperature increases to 140 degrees, the vernatherm piston/pin expands out and closes/restricts flow through the small holes and now all the cooling water that can exhaust through the cylinder head cover to cool it, is dependent on the water pressure from the water pump pushing the thermostat back against the big spring (the relief valve spring). So, if the water pump is not in perfect condition, at idle speed or slow speeds, it can't generate enough pressure to push the thermostat back. Or it it easy to push back with little water pressure once the vernatherm pin expands out and closes the little holes?

 

[Klink]

All the other Johnson/Evinrude engines I've had (all from the 1990's) 6hp, (2) 25hp, 115hp, and even a Yamaha 115, all registered about 138 at the cylinder head on the surface on each cylinder, when I tested them with a flusher. This 70hp is at 168-170 on the bottom cylinder, and the cooling passages in the cylinders and head are spotless. BRP changed the style of the thermostat from bigger holes to the small holes in the new model. With the old model, and the vernatherm stuck in the off position, the temperature at the cylinder head on the surface on each cylinder was 100 degrees. That is why I replaced the thermostat. With the new thermostat, with the vernatherm in the off position the temperature is 168-170. Apparently for this engine, 168-170 is normal? Is it?

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