40 HP 1976 Johnson Seahorse Model # 40R76R

[newk0001]

Hello everyone. I have just joined this forum and this is my first post ever on this site. I own a 1976 40 HP Johnson Seahorse model # 40R76R and I was curious as to whether or not anyone out there knows if this engine has a thermostat. If it does, where is it? I've seen other Johnson engines that have a thermostat but in the manual for my engine I can't find anything about a thermostat anywhere. If it, in fact, doesn't have a thermostat in it why? Would there be any advantage to installing a thermostat in the engine. Thank you for your time.

 

[Joe Reeves]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

The 1976 40hp Johnson does not incorporate a thermostat, nor is there any way you could possibly install one. On that model, it is not required.

 

[newk0001]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Okay, thank you. Can you shed any light on the subject as far as why it doesn't need a thermostat but other motors do require them?

 

[gm280]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

I second what Joe stated above. I have a 1976 40 HP Johnson 40E76R model. I am in the process of a complete rebuilt presently because the previous owner hit something with it and cracked the skeg, broke off the startboard side of the cavitation plate, bent the prop and all the foot oil was gone but replaced with rust... So I disassembled the entire motor...every little nut, bolt, washer and screw. I am now reassembling it after a new paint job to all the parts...

 

[Joe Reeves]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Okay, thank you. Can you shed any light on the subject as far as why it doesn't need a thermostat but other motors do require them?

I was never in the engineering field so I can't get into what you're asking. However, I can say that the 1976 40hp design was somewhat of a upgraded copy of the 1957/1958 35hp series that did not incorporate a thermostat with changes of course.

 

[F_R]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Okay, thank you. Can you shed any light on the subject as far as why it doesn't need a thermostat but other motors do require them?

You have to travel back in time to answer that one. Before the late 1950's no outboard had a thermostat. But then 'stats were added
to better control operating temperature for better running under widely differing lake and air temps. Among other things, this allowed fixed jets in their carburetors. Along with the thermostat, cooling systems were also modified. Some have recirculating systems, others have dual flow paths. So those systems depend on thermostats to operate correctly. Now, as for your 40hp, that is a resurrection of the old design motors dating clear back to the 1950's (to keep the cost down). They run just like the older motors, very well, but maybe not as well under all possible conditions without having to readjust the carburetor, etc.

 

[newk0001]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Okay, thank you guys so much for your input here. Joe had stated earlier in a post that there is no way to install a thermostat on the particular motor that I have. Taking that into consideration I'm almost starting to think that it would be a better idea just to get a new motor simply because this motor runs fine when the ambient air temperature and lake water is relatively cool but as soon as the water warms up to about 72 degrees Fahrenheit and the air temperature is into the mid-80's the engine over-heats and shuts down; rendering it useless for about 90 minutes. I don't know for certain if installing a thermostat would alleviate this symptom but it sounds like I don't have many other options to consider in the way of repairing the cooling system. It's probably useful information for anyone that may be reading this to know that I have already installed a new impeller and pump housing on the engine and even though the lines are free of debris there has NEVER been any water coming out of the unit. I've heard that water coming out of the exhaust housing is a tell-tale sign that the cooling system within the motor is working correctly. However, mine is not. If anyone has any input for me about this it would be greatly appreciated. Thanks again for your time and I look forward to hearing from you.

 

[TN-25]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

All the thermostat will do is close when it wants the water to heat up to reach the optimal temperature. Your 40 simply has the water flowing all the time the motor is running. That in itself can’t explain why your motor is overheating. You have a new impeller; is the keyway engaged in the impeller? Is the impeller housing sealed up properly? Can you check to see if any water tube grommets are distorted and possibly blocking the water? Is the water tube cracked, or is it possibly not seated all the way? Is the water intake by the prop clear? Sometimes mud daubers can block it up if it has been outside or in the shed. When the motor overheats, see if the block is too hot to touch, indicating poor or no water circulation. If the block isn’t too hot to touch I would bet that an ignition component is failing under load (coils). Another slight possibility is vapor lock.

The lower unit on your 40 very closely resembles and is not far from the original 1951 Big Twin 25. By 1955 they added the rubber mounts, water tubes and called it good. After 1958 Johnson & Evinrude dropped that design for a couple of years in favor of a “Super Quiet” double-walled lower unit that used a thermostat & extra water circulation paths. Gale kept the older lower unit in production in the 22, 25, 35 & 40-horse motors from 1955 right through 1963-ish (yes, even on the 40). Meanwhile Johnson & Evinrude resurrected the old lower unit to create an economy 28 for 1962, enlarging it to 33 for 1965. The 40s from 1960 through 1970 all had the Super Quiet lower unit with the thermostat, (except those Gales in the early 1960s). When the new 50-horse looper twins came out for 1971, the 40 took on the role of an economy engine. For that they combined the simpler, non-thermostat lower unit of the 33 with the 40-horse block. The 1971-onward 40s were now simple workhorse motors while the 50 was faster and more sophisticated.

 

[gm280]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

I wouldn't be so quick to dispose of your 40 Johnson being it has no thermostat. Being how there are large numbers of them still out there and doing a great job speaks for their reliability. If you are having temp problems, you need to look into why and not simply blaming the lack of a thermostat. Others run them year round without one issue... Something else is going on with your engine... JMHO!

 

[TN-25]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

I wouldn't be so quick to dispose of your 40 Johnson being it has no thermostat. Being how there are large numbers of them still out there and doing a great job speaks for their reliability. If you are having temp problems, you need to look into why and not simply blaming the lack of a thermostat. Others run them year round without one issue... Something else is going on with your engine... JMHO!

Exactly!

 

[F_R]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Okay, thank you guys so much for your input here. Joe had stated earlier in a post that there is no way to install a thermostat on the particular motor that I have. Taking that into consideration I'm almost starting to think that it would be a better idea just to get a new motor simply because this motor runs fine when the ambient air temperature and lake water is relatively cool but as soon as the water warms up to about 72 degrees Fahrenheit and the air temperature is into the mid-80's the engine over-heats and shuts down; rendering it useless for about 90 minutes. I don't know for certain if installing a thermostat would alleviate this symptom but it sounds like I don't have many other options to consider in the way of repairing the cooling system. It's probably useful information for anyone that may be reading this to know that I have already installed a new impeller and pump housing on the engine and even though the lines are free of debris there has NEVER been any water coming out of the unit. I've heard that water coming out of the exhaust housing is a tell-tale sign that the cooling system within the motor is working correctly. However, mine is not. If anyone has any input for me about this it would be greatly appreciated. Thanks again for your time and I look forward to hearing from you.

What???? Are you telling us that it has never discharged water out of the exhaust relief hole on the backside of the midsection? That seems totally wrong. It shouldn't last 10 minutes under that condition before burning itself up.

 

[gm280]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Okay, thank you guys so much for your input here. Joe had stated earlier in a post that there is no way to install a thermostat on the particular motor that I have. Taking that into consideration I'm almost starting to think that it would be a better idea just to get a new motor simply because this motor runs fine when the ambient air temperature and lake water is relatively cool but as soon as the water warms up to about 72 degrees Fahrenheit and the air temperature is into the mid-80's the engine over-heats and shuts down; rendering it useless for about 90 minutes. I don't know for certain if installing a thermostat would alleviate this symptom but it sounds like I don't have many other options to consider in the way of repairing the cooling system. It's probably useful information for anyone that may be reading this to know that I have already installed a new impeller and pump housing on the engine and even though the lines are free of debris there has NEVER been any water coming out of the unit. I've heard that water coming out of the exhaust housing is a tell-tale sign that the cooling system within the motor is working correctly. However, mine is not. If anyone has any input for me about this it would be greatly appreciated. Thanks again for your time and I look forward to hearing from you.

newK0001, I basically have the exact same OB as yours and since it is totally disassemblied and being put back together now, I know all the water passages are free and clear on my engine. I also installed a Tale tell tube in the very top of the block to show me that the water system is working okay. You may consider doing that to yours for verification that your cooling system is working and not plugged as well. If you are interested, I'll snap some shots to show you where and how I did it...

 

[newk0001]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

F_R, yes sir. That's exactly what I'm telling you. Perhaps I should clarify a bit though. It has never discharged water out of the exhaust relief hole in the 8 years that I've owned it. I haven't used the motor in about 2-3 years and before that I only used it in cold weather conditions as soon as I found out that it has the overheating problem when it gets really warm out.

 

[newk0001]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

gm280, I am absolutely interested and I would appreciate the hell out of that if you would be generous enough to snap some shots to show me where and how you did this to your motor. Thank you very much.

 

[newk0001]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

TN-25, thank you for the in-depth explanation. It is exactly what I was looking for. It seems that so many people give yes and no answers to questions and never answer the how or the why. I appreciate it and thank you to all of you who have helped me with this problem up to this point.

 

[gm280]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

F_R, yes sir. That's exactly what I'm telling you. Perhaps I should clarify a bit though. It has never discharged water out of the exhaust relief hole in the 8 years that I've owned it. I haven't used the motor in about 2-3 years and before that I only used it in cold weather conditions as soon as I found out that it has the overheating problem when it gets really warm out.

I've reread your orginal post that you talked about this OB over heating but only in the warmer weather. But if you had a thermostat it would actually run even hotter then as well, because the thermostat would stay closed to allow the water to warm up. So being how you don't have a thermostat it should run very cool all the time... If you are experience over heating you have something plugged in the water passages...

 

[newk0001]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

gm280, that makes perfect sense. Is there a way to check if the water passages are clear without taking the lower unit and exhaust housing completely apart or is that just the nature of the beast? If it is, that's fine, I would just like to know before I go doing any unnecessary work on this thing.

 

[kodibass]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Here is what you should see from your motors blubber hole

1975 40 Johnson - YouTube

 

[gm280]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

gm280, that makes perfect sense. Is there a way to check if the water passages are clear without taking the lower unit and exhaust housing completely apart or is that just the nature of the beast? If it is, that's fine, I would just like to know before I go doing any unnecessary work on this thing.

I would remove the lower foot section again and see if you can see anything logged in the tube going up to the head of the engine from the water housing for starters. That tube should fit very nicely into the water pump housing and the output grommet. You could even try to blow some air through that tube as well, because there is nothing in the head section that would channel the water differently than just a free unobstructed flow around the cylinders and out the mid section or exhaust housing section. If there is any obstruction it would have to be at the gasket area where the power head bolts to the mid or exhaust housing section. That is the only place in my opinion where there could be a problem if it is blocked looking at how it is built. And I will get you some good pictures to install that Tale Tell tube. You will be amazed how easy it is going to be... Then when you start this OB again it will show you absolutely if you have a water pump and cooling system working or not...

 

[gm280]

Re: 40 HP 1976 Johnson Seahorse Model # 40R76R

Okay newk0001, here is how I installed a Tale Tell stream on my Johson OB. If you look at the very top of your OB you will see two cast bosses just behind the head of the engine where the plugs are installed;



This is my OB just before I disassembled it for a complete rebuild... I know it looks really ratty...PO what can I say?

This is where I installed the 90% brass fitting;



This is the same engine disassembled and sandblasted before any new parts go in...

I used a 90% 1/8" NPT brass fitting because I'm not sure there is enough area between the top of the block and the cowling to fit a straight fitting and the tube and loop from the tube. I bought the fitting on EBay and the 1/8" NPT tap also. Neither were very expensive...just a few dollars.



I used a 1/8" drill bit to drill through the existing threaded cast boss area. Seems they cast those two threaded bosses there for some reason but for what I just don't know. But as you drill down with the drill bit use some grease around the drill bit so as the filings are cut they get stuck to the grease instead of going into the hole. Don't worry if you get a few in there because this areas is nowhere near the impellor pump and would probably just wash out when it starts up... But drill slowly becasue just under this area is the water jacket for the top cylinder;



I don't know if you can see the top cylinder in this picture but that is all the room between the top of the block and the top cylinder (about a ?” or so), so just drill easy. Once you drill through, drill the same hole for the actual tap and tap it for a few good threads. The NPT tap is a tapered tap so use the appropriate drill (I think it is listed on the tap) and again tap slowly and use the grease again. Once you are satisfied you have tapped it far enough fit the brass fitting and adjust to your liking... Nothing really to it. As for the output hole in the lower cowling section, just pick a place toward the starboard rear section of the lower cowling plate and put a fitting there to receive the hose you installed on the brass fitting you just fitted... Now when you start up your OB there will be a constant Tale Tell stream flow letting you know for certain your water pump is working... I sure hope this is helpful and understandable...