Evinrude 120 Cooling Problem

[DancingPaul]

This past weekend my engine overheated twice. The impeller and thermostats were replaced very recently. The overheating problem only occurs when running at 3,500 rpm or above. I noticed that when I get above 3,000 rpm my water pressure starts dropping. When running below 3,000 the gauge indicates about 7-8 pounds pressure. When I get above 3,000 rpm the pressure drops to 2-3 pounds pressure. The water coming out of the site check hole seems fine at low rpm but seems to drop off at higher rpm.

Questions:

1. Shouldn't the water pressure gauge show increased pressure rather than decreased pressure at higher rpm?

2. Any ideas about the cause of the problem?

Thanks

 

[ezeke]

Re: Evinrude 120 Cooling Problem

What year is your motor, the 120 cooling systems vary depending on the model?

 

[DancingPaul]

Re: Evinrude 120 Cooling Problem

1988, 89

 

[Dhadley]

Re: Evinrude 120 Cooling Problem

Sounds like the line for the gauge is hooked into the wrong place. Most likely you have it T'd into the overboard line. It should be T'd into the line that comes from the adaptor plate and goes to the water control valve behind the throttle arm. That is, assuming you really do have a 1988 or 89 V4 looper.

 

[nymack66]

Re: Evinrude 120 Cooling Problem

Please verify your thermostats are installed correctly , To test remove both and test the engine .I have seen em installed in-correctly ...Mine was

 

[Dhadley]

Re: Evinrude 120 Cooling Problem

It's really not likely looper thermostat assemblies are installed incorrectly since they will only fit one way. However, they must be there for the motor to operate properly with that cooling system. Again, we're assuming the motor is a 88 / 89 V4 looper with the stock water control valve in place. If it's been upgraded to the 93 style cooling system then that's a little different.

 

[Daviet]

Re: Evinrude 120 Cooling Problem

What about a slight head gasket leak pressuring the cooling system and restricting water circulation? Just thinkin.

 

[kenmyfam]

Re: Evinrude 120 Cooling Problem

The thermostats on mine are either in correctly, not in at all or you have broken something putting them in wrong.
Difficult to screw up.
Have you done a temperature test on the heads ???

 

[ezeke]

Re: Evinrude 120 Cooling Problem

Be sure that the small holes in the thermostat cover and cover gasket are open, or the water control valve will not function properly. If they are both open, then it is likely that your water control valve needs to be serviced as Dhadley indicated.

 

[DancingPaul]

Re: Evinrude 120 Cooling Problem

Thermostats are both new. and the definitely only go in one way. Engine runs at 140. except when there's low PSI,

T is in the line coming from the starboard bottom of the block in the line going into the valve behind the throttle.

seems to get 15psi if i idle it high (4000) at the dock. When moving, its at 5 and drops to 1,2 PSI when i speed up. if i slow down to a crawl it stays low. Only when I pop it in neutral for a couple of seconds do i regain above 5-10.

this is definitely a mystery to me. would the control valve be opening too much? causing very low pressure at the gauge?

 

[nymack66]

Re: Evinrude 120 Cooling Problem

Assuming your pressure gauge is T in correctly then I will check the impeller you may have shared the key on it or broke off a blade and its slipping at the higher RPMS..

 

[kenmyfam]

Re: Evinrude 120 Cooling Problem

How about a photo showing us all the water control valve and where the pressure gauge is teed into the system.

 

[DancingPaul]

Re: Evinrude 120 Cooling Problem

I'll try and get a photo this weekend.

I have more information.

I got the engine up to temperature at the dock. than upped the RPMs to 5000. water pressure goes up to 20PSI. I let it run like this for 5 minutes. Pressure stayed at 20.

So now I'm totally lost. What would be different when I'm moving than when I'm at the dock?

 

[ezeke]

Re: Evinrude 120 Cooling Problem

It's a wonder that you did not blow the engine up; you should never run a two stroke higher than 1500 RPM unless it is in gear.

According to the Teleflex chart, the pressure should be at 12-25 PSI at 5,000 RPM, but that will depend on where the pressure gauge is attached and if the line to the gauge is clear and free of water. The elbow at the adapter plate needs to be clear as well, and the Water Control Valve has to be functioning properly.

 

[kenmyfam]

Re: Evinrude 120 Cooling Problem

I'll try and get a photo this weekend.

I have more information.

I got the engine up to temperature at the dock. than upped the RPMs to 5000. water pressure goes up to 20PSI. I let it run like this for 5 minutes. Pressure stayed at 20.

So now I'm totally lost. What would be different when I'm moving than when I'm at the dock?

How much motor is in the water when you are planing ???