Evinrude overheating at 3/4 throttle or more

[iggyw1]

Hi again guys,

Same motor, different problem! I need some help again please. I made some headway, thought I had things figured out, but no way. Again, my motor is a 1965 Evinrude Speedi Four. Four cylinder, model # 75553. History: When I first bought it a few months ago, I had a problem with it overheating within two minutes at idle speed. I changed the water impeller and housing to no avail. I sent it to a mechanic. He got it cooling good at his shop. When I took it out the other day, it registered 145 to 147 degrees on the temp gauge in rough seas so I only ran it about 1/2 speed. Today, the lake was calm, so I tried it wide open. Ran sweet!! Good speed and easy planing. No miss fire. Starts and runs great. Problem: At 3/4 to WOT, it overheated where I had to shut it off. Took the cover off and let it cool down. It was very hot to the touch on both banks of pistons. After it cooled down, I started it back up and water was coming out good from the rear of the motor like it should,. (no pee stream, but a real good spray that looked good). I drove at 1/2 throttle and slightly more and temp was good. At 3/4 throttle, it started heating up and steaming out of the water discharge at rear of motor. I backed down on the speed and water temp went down and steam stopped coming out. Every time I would speed up to 3/4 throttle or greater, it would start to heat up again.

When I got back to the dock, I removed the plugs. No sign of water on any of them. All four looked normal like they should. Now I am wondering if the exhaust gases may be entering the cooling water somehow??? If so, how can the exhaust gases get into the cooling water?? Is it normal if the exhaust gases are getting into the cooling water in some way, for it to be ok at lower speeds and rpm's?? ( I do not have a tach on the boat, but I plan on installing one if I get her running without overheating).

What are your thoughts on this problem guys? I'm all ears. Thanks!!

 

[F_R]

Yes, exhaust gas can get into the cooling system through the recirculating water tube. But I'm not saying that is the problem (could be, I suppose). How about it, is the water intake screen in place? Just forward of the underwater exhaust outlet snout. It can't get water at high speed if it is missing. Also, is it too high on the transom?

EDIT: By chance, has somebody removed all the guts from the thermostat housing? If the relief valve is not in there, it will send exhaust back down the recirculating tube to the water pump, big time. Can't expect to be able to toss stuff and expect it to work.

 

[iggyw1]

Yes, exhaust gas can get into the cooling system through the recirculating water tube. But I'm not saying that is the problem (could be, I suppose). How about it, is the water intake screen in place? Just forward of the underwater exhaust outlet snout. It can't get water at high speed if it is missing. Also, is it too high on the transom?

EDIT: By chance, has somebody removed all the guts from the thermostat housing? If the relief valve is not in there, it will send exhaust back down the recirculating tube to the water pump, big time. Can't expect to be able to toss stuff and expect it to work.

I suppose the mechanic could have screwed up and left something out of the stat. At one time, I checked it out myself, but I am positive I put things back correctly. I checked the T-stat to make sure it was working. Screen is in place on the water intake, and the motor is on the transom low enough so the water level is up where it should be. I talked to the mechanic that worked on it this morning. He said it definitely sounds like there is some pressure getting into the water line from either a head gasket or the exhaust gasket and he mentioned some other gasket which is right under the power head (adapter to power head gasket). He said it could be any one of these gaskets causing the problem, but the power head gasket very rarely causes any problem at all. He told me to do a compression test which I will do when my son comes over tomorrow with his compression test gauge. ( I just bought one on Crags list and it is junk. Doesn't work). The motor just seems to run too good to be a head gasket in my opinion, and no signs of water in the pistons at all. Plugs look normal. I can get the head gaskets for $26 each, and mechanic wants $200 to replace them both. He recommended doing both sides and not just one side. I agree with him and the price sounds good for labor to me, but there should be some way to test things out to see what the culprit would be.

I cannot find out in any of my manuals what the compression should be. Do you know what I should expect on the compression? I do know that the compression should be close in every cylinder, but what should they read??? Thanks!

 

[Bosunsmate]

$200 would get you a very very nice torque wrench and over a hundred left in change

 

[F_R]

There are two plastic valves in the thermostat. One is pushed open by the vernatherm, and the other is pushed open by water pressure. The second one is the one I am suggesting.

With all due respect, I don't believe the gaskets are the problem. But l won't be offended if you report back that you changed them and it fixed it.

 

[iggyw1]

There are two plastic valves in the thermostat. One is pushed open by the vernatherm, and the other is pushed open by water pressure. The second one is the one I am suggesting.

With all due respect, I don't believe the gaskets are the problem. But l won't be offended if you report back that you changed them and it fixed it.

I really don't feel that the gaskets are at fault either, especially the head gaskets. As I said, the motor really runs great now except for the overheating problem. I think what I will do is replace the thermostat parts completely and give that a try to see what happens. I will change both of those plastic valves along with the springs and the vernatherm as well. I can do that myself because I took it all apart once to test the vernatherm. Also, I was looking at the motor tonight, and it seems like a breeze to change those head gaskets myself too. I have some manuals here that are pretty good, and I have some mechanical ability. On my last motor, (Evinrude 1965 selectric shift) I rebuilt the entire lower unit electromagnets in the gear housing and resealed the lower unit, so I should be able to handle the head gaskets if they need to be replaced. But I will definitely replace the T-stat internals first.
Thanks for the help!
After I try the T-stat replacement, I will report what happens on the lake.

 

[iggyw1]

I really don't feel that the gaskets are at fault either, especially the head gaskets. As I said, the motor really runs great now except for the overheating problem. I think what I will do is replace the thermostat parts completely and give that a try to see what happens. I will change both of those plastic valves along with the springs and the vernatherm as well. I can do that myself because I took it all apart once to test the vernatherm. Also, I was looking at the motor tonight, and it seems like a breeze to change those head gaskets myself too. I have some manuals here that are pretty good, and I have some mechanical ability. On my last motor, (Evinrude 1965 selectric shift) I rebuilt the entire lower unit electromagnets in the gear housing and resealed the lower unit, so I should be able to handle the head gaskets if they need to be replaced. But I will definitely replace the T-stat internals first.
Thanks for the help!
After I try the T-stat replacement, I will report what happens on the lake.

QUESTION: What would happen if I removed the plastic valve that opens with water pressure from the T-stat?? If I removed it, then took a spin on the lake, and IF that is my problem, would that spin on the lake let me know this since that valve would not be in place to malfunction? Just a thought I just had.

NOTE:
I do not mean to remove it permanantly, as I know it is needed so the motor will not over cool or it would not be there, but I mean just a TEMPORARY removal for a short test period.

 

[iggyw1]

I ran a compression test today on the four cylinders and not good. I got compression of 90 on three of the cylinders and 88 on the fourth one. Seems they are all low! Originally, I had (and still have) an overheating problem at high RPMs. I understand that ha blown head gasket can cause an overheat problem. Now, I am wondering if the bad head gasket can also make you have low compression? Maybe a blown head gasket on both heads?

I am now considering pulling the head covers and the heads to see what things look like inside. Might not be worth the expense of repairs if it needs a total rebuild since I cannot do the work myself. I am probably better off getting a newer motor for the price of a total rebuild.

 

[Bosunsmate]

QUESTION: What would happen if I removed the plastic valve that opens with water pressure from the T-stat?? If I removed it, then took a spin on the lake, and IF that is my problem, would that spin on the lake let me know this since that valve would not be in place to malfunction? Just a thought I just had.

NOTE:
I do not mean to remove it permanantly, as I know it is needed so the motor will not over cool or it would not be there, but I mean just a TEMPORARY removal for a short test period.

That helps keep pressure in the system so if you removed it the motor might not overheat and so you might consider that that was the problem however it would not have the correct pressure occurring in that test so something which goes wrong under that increased pressure wouldnt show up.
Youd have to have a significant break in the system for it to overheat with the valve removed

 

[Bosunsmate]

I wouldnt be concerned about that compression, its quite even. If its got enough power for what you need then thats the motor you want.
You could run some seafoam through it to see if that gets the numbers up.
Have a look at your spark plugs and have a look at the top of the pistons through the spark plug hole.
You are looking for signs of water entry or piston head damage. Water entry can show up as rust on the sparkplug electrodes and also the pistons will look steam cleaned. Any dings on the piston head can mean broken rings.
Pulling the head would tell you a lot more as you can then see clearly the cylinder walls

 

[iggyw1]

I wouldnt be concerned about that compression, its quite even. If its got enough power for what you need then thats the motor you want.
You could run some seafoam through it to see if that gets the numbers up.
Have a look at your spark plugs and have a look at the top of the pistons through the spark plug hole.
You are looking for signs of water entry or piston head damage. Water entry can show up as rust on the sparkplug electrodes and also the pistons will look steam cleaned. Any dings on the piston head can mean broken rings.
Pulling the head would tell you a lot more as you can then see clearly the cylinder walls

Thanks for your reply. This motor does give me enough power. When I was going WOT the other day (til she overheated) I was doing 29 MPH on the speedo. It planed very easy too. I was going WOT then I noticed on the gauge I installed that the heat was going up fast. Then I let it cool down, started her back up and temp was good at less than 3/4 throttle, then would start heating up at more than 3/4, I would back down and it would cool down again, no problem. Starts very easily (even when cold) and runs real sweet but overheats at high RPM. I ran a heavy dose of seafoam in it (one 16 oz. can to two gallons of fuel, ran then sat, ran then sat, etc. a few times. Piston tops look normal. The spark plugs were a bit shiny (not all the way, but a little bit on all plugs) but I credited this to the seafoam rather than water. (possible)? Looked for a crack in the block, did not see one. (although I think it is running too good for the block to be cracked).

Someone else told me that the compression is ok as long as they are even, so I go along with this, thanks. I am going to order the gaskets I need for the heads, the head covers and also the by pass covers. Can you tell me what I will see if I take the bypass covers off? They are easy to get to, so I figured I would take a look in there, but I don't know what I will be looking at/for???
Thanks!

 

[F_R]

You will be able to see the side of the piston and rings. You will also be able to poke at the rings to see if they are stuck in the grooves or not.

 

[Tim Frank]

Have you verified that your temp gauge is accurate?

 

[iggyw1]

Have you verified that your temp gauge is accurate?

Yes I did. I also checked the heads with a infrared temp tester. The gauge actually reads 2 degrees cooler than the infrared.

 

[Bosunsmate]

if you press on the rings, if they are ok they will feel springy, although a very firm springy, you have to press them quite hard, i use a thick screwdriver to to this so i dont gouge them, if you get no movement they are stuck or snapped.
how far above or below is your anti cavitation plate from the bottom of your boat? im wondering if you are getting air sucked back in at high speed

 

[F_R]

That is a very good point. Shoulda thought of that. That motor was not designed to run with the plate above the bottom. Gotta have the intake screen down in the water.

 

[iggyw1]

if you press on the rings, if they are ok they will feel springy, although a very firm springy, you have to press them quite hard, i use a thick screwdriver to to this so i dont gouge them, if you get no movement they are stuck or snapped.
how far above or below is your anti cavitation plate from the bottom of your boat? im wondering if you are getting air sucked back in at high speed

My cavitation plate is about (2) inches below the bottom of the boat. I am looking into a motor I saw on Craigslist in my area. It is a 1977 Johnson Stinger 75 h.p. Sounds like a real good motor by the listing. Not too far from me, so I will go see it, if the guy ever replies to me. So far, no reply from him. He put a lot of new things on it and says it runs great. Holds 15 pounds pressure and vacuum in lower unit ad says he will run it for the buyer. I might be better off with that motor. He will take my Evinrude as a trade in and give me an allowance for it. Just wondering if that is a good motor in general? It is a three cyl. motor and it looks lighter (smaller) than the Evinrude I have now (1965 75 h.p. Speedi-Four). Being the same horse power as each other, would I get more power from the four cyl motor than the three cyl motor?

 

[F_R]

That three cylinder looper will make your old V4 look foolish. And on way, way, less gas

 

[iggyw1]

That three cylinder looper will make your old V4 look foolish. And on way, way, less gas

I got in touch with the guy. He says the motor is up north right now, but he will have it home in a few weeks. He says he will run it for me. He does not want my motor because he says it eats way too much gas!! (it does). He has controls I will need too. He said it uses the red wire set up (what ever that is). There is no way I can install the motor and controls. The controls he said I need has the key switch in it too, and is a one lever control box. I have two levers now and the key is in the dash.

Does anyone have any idea on what I can expect to pay for someone to take my old motor and controls off and put the new ones in? I also need to plug the holes in the transom if the holes are not lined up the same. Would a plate of some type work with the current bolt, washer and nut that the motor is mounted with??