Overheat in Full Throttle

[colbyjax]

I just bought a '93 140hp V4 Evinrude.

It idles fine, but after running at high RPMs on a plane the overheat alarm starts to go off, then after it cools down a bit I can run in idle again just fine, but once I put it back into high RPMs it does the same thing. I noticed the stream indicator has water going through it, but does not appear to be a really strong/steady stream (aka **** stream).

After getting the SELCO and reading some posts I figured I would go ahead and do some work on it.

Did the following:
- Rebuilt Water Pump/Impeller with a Kit
- Replaced both Thermostats
- Put a piece of wire up the Stream Indicator.
- Checked Compression and verified there is no head gasket leak

I haven't taken it out and tested it to see if it happens again, but when I hook up the garden hose, it still appears to be getting water through the indicator but not a strong uniform stream.

When I looked at the indicator, it has a T attachment. The small tube that connects to the T, goes into the engine around the port thermostat. The big tube that comes out of the T and appears to go straight down into the stream indicator, isn't connected to anything on the other end. It might be a pressure relief valve or something (not sure, any help on that appreciated). I wanted to know if there is anything else I should check or just put it in the water and test it again?

Thanks for any help.

 

[HighTrim]

Re: Overheat in Full Throttle

You will not be able to test the water pumps operation in the driveway on the muffs, since the hose is "force feeding" the necessary cooling water anyways.

When you had the lower unit down, did you flush and backflush the water line to ensure that it was free of debris? Clean out the water intake area?

Take her out on the water and take her for a rip, if the alarm sounds, shut her down immediately. Will water sizzle on the head? Can you hold your hand on the head for a 1, 2, 3 count? Better yet, measure the actual temp with an infrared thermometer. If it is in fact overheating, you may need to look at the water deflectors in the head. If it is not overheating, test the heat sensors as per your manual.

Let us know what you find.

 

[HighTrim]

Re: Overheat in Full Throttle

...and have a read here

http://forums.iboats.com/showthread.php?t=222677

 

[colbyjax]

Re: Overheat in Full Throttle

Thanks for your reply.

The vents are clear.

I did not flush/back-flush the water line when the lower unit was down. How is that done, do I just take a hose spigot and shoot it up the intake where the water pump outlet connects to the upper unit?

I read the article you attached. I can see that my tell-tale is the small tube that is connected to the port side of the engine and hooks to the T. Still not sure what the big tube that is connected to the T is for (the one that seemingly terminates on the other end).

I will take her out soon and see if it overheats and test the temperature as described.

Thanks again for your help.

 

[ezeke]

Re: Overheat in Full Throttle

There are no water deflectors in your particular 140HP engine.

The problem lies in the water pump, the cooling circuit, or the thermostats.

The tell-tale lets you know that the water pump functions, but tells you nothing about the circulation of water through the cooling passages of the engine itself.

If you have not changed the water pump impeller, do that first.

Then, the thermostats, housing and hardware, including the seats, should be examined and tested for function and cleanliness.

 

[colbyjax]

Re: Overheat in Full Throttle

Thanks for the advice so far.

Ok I took it out today after the work I've done and I do get a nice strong stream from the tell-tale this time. But I am still having the overheating problem.

I can keep the engine going in idle just fine, but after about ten minutes of 4500+ RPMs the alarm sounds and engine starts slowing down automatically.

I was able to put my hand on the head for a count of three without issue, but if I kept it there to about five it would burn.

Recap of what has been done:
- Changed Entire Water pump housing/gaskets/impeller
- Changed Thermostats and gaskets
- Cleaned out tell-tale tube
- Verified head gasket isn't leaking with compression tests.
- Checked Water Intake vents, they are clear

* I didn't backflush the system when the lower unit was down. Should I take off the lower unit again and do this now?

* It is a '93 motor, not sure what the shape of the cooling passages are, maybe need to be cleaned somehow?

* My best guesses at this point are: malfunctioning sensor, crud on the cooling passages, or clogged cooling passage.

Any advice helpful. I'm stuck

 

[HighTrim]

Re: Overheat in Full Throttle

What you need to do is determine if in fact it is overheating.

USUALLY, you cannot hold your hand on the block of an outboard that is in excess of 180* for 3 seconds. I keep an infrared thermometer in my toolbox for just such an occasion, but if you do not have one, any friends that do? I got mine for about 30 bucks, comes in handy in the house as well. Thermomelt sticks would also help determine the heads temp.

If it IS overheating, there is likely a restriction in the cooing circuit. Just a thought, is there a pinhole in the t stat assembly on that model? Someone may be able to verify. If this hole is plugged, the cooling water cannot reach the other side of the stat, telling it to open. This will cause an overheat condition, in about the time you state yours happens in.

If it is NOT overheating, test your heat sensors as per your manual.

 

[colbyjax]

Re: Overheat in Full Throttle

Well I was finally in town long enough to test it out. I ran it today and took an infrared thermometer with me. It is definitely overheating. Both Sides at the tops of the cylinders were running great when I was in low RPMs (~2500) (temp was around 100 degrees) however when I got on a plane and throttled back to 5000 RPMs the overheat warning went off again. I pushed it back down to Neutral and measured the temp on both sides (It was between 180 and 200 degrees on both sides)......took a while to cool down.

I am not really sure where to go. There is a small pin in the middle of both thermostats, I made sure to reinstall that. The odds that both therms would be clogged I would think is remote. I am stuck on what to check now.

Totally at a loss now

 

[ezeke]

Re: Overheat in Full Throttle

The thermostats on the 1993 V4 140 motors with a model number ending with a suffix of S, used the more recent thermostat 434137. which is a complete assembly colored black. I found that they improved the cooling function and have since used them on my 1988 140 and on my 1990 225. I would recommend that you try them.

Some earlier models also had problems with the seats at the back of the thermostats which you may want to inspect. The problem was corrosion, which deformed the seal. The ones with an aluminum shield were generally replaced with a newer one piece seat #336416.