Johnson 1974 70hp water pump paranoia

Hi. I need some advise on my 1974 Johnson 70hp. I hadn't used my boat in 5 years (I have a 4 year old daughter - hmmmm corelation?) and I want to get it back out on the lake.

I had left the gas in the carbs and lines 5 years ago - bad idea. I totally cleaned out the carbs and rebuilt them. It was pretty easy I thought. Anyways it starts up and runs great now!

I also rebuilt the water pump because even when I owned it and was using it almost every weekend, I had never rebuilt it so I figured it was time.

I thought I got it all correct but am I paranoid that it is not pumping. I'm afraid I did something stupid like letting the woodruff key slip out or something.

From what I can tell this engine does NOT have a tell-tale hole. At least with muffs on I don't see water coming out of any holes. I've read conflicting things on the internet, and none of my shop manuals specifically say. And I don't remember if I saw one 5 years ago or not on this model.

I saw the sticky post about adding one, or threads about adding a water pressure gauge - I'm afraid mods like that are a little more than I am comfortable with.

What are my other options for knowing that it is cooling?

I did ground out the temp sensor to see if the overheat buzzer sounds at the shifter, and it did buzz. I dont know if I can rely on that temp sensor doing its job though. How do I know it will detect the correct temp? Should I just hope for the best and run it and see if it goes off?

Can I shoot one of those laser temperature devices to measure the exterior temperature of the water cooling jacket to see how hot it gets? What would be an acceptable temperature. After idling for a bit with muffs it was MUCH too hot for me to leave my hand on it so I shut the engine back down right away to prevent damage.

I guess I can take the lower unit back off and look at the water pump to make sure the impeller is spinning and the key is on. I used gasket sealer though so I'm not sure what I will have to do if I take it apart - if I will need new gaskets again.

Do I need to submerge it in water (as opposed to the muffs) and rev it up? Will I see water spit out the 2 holes (that I thought were exhaust holes) on the back of the engine? I can submit a picture of them if it helps.

What about a thermostat? Does this model have one and should I check it for functionality?

Please give me some advise on how I can be sure its doing its job.

Thank you very much!

Jeff

Re: Johnson 1974 70hp water pump paranoia

You can use a the heat sensor, at the top of the block, just above the spark plugs, 140-145 is what you want. are you sure the water tube lined up when you reattached the lower. they tend to slide to the side, if not correctly lined up. drop the lower and recheck. the tstat is in the bottom of the water jacket on then cylinder head, go here engine diagrams, you can see your complete motor "http://www.evinrude.com/en-US/Accessories/Introduction.htm"

Re: Johnson 1974 70hp water pump paranoia

It should blow water out the holes on the back any time the motor is running, whether thermostat is open or closed. Running on muffs is not a good indicator of whether a water pump is working. Only good test is to put it in the water and start it up.

The horn in the control is a nice feature, but a false sense of security. They often go off after the motor is cooked.

Re: Johnson 1974 70hp water pump paranoia

Putting a tell-tail on that motor is realy easy.


If you dont want to remove the head then go by what iwombat has posted on the location for the service bulletin.

Re: Johnson 1974 70hp water pump paranoia

Don't "rev it up" over about 1500RPM or bad things may happen when running on muffs or in a trash can! Been there, done that.

Re: Johnson 1974 70hp water pump paranoia

When you drop the lower unit to change the impeller, there will be a rubber grommet on top of the impeller housing. Make sure that this is seated correctly and not shoved into the impeller housing restricting water flow like TD said, Ive seen this happen many times. Also while the lower unit is down, run some compressed air or the garden hose up the water line, taking out one t stat at a time, letting the air/water exit there. This will ensure that the water line is not clogged.

Re: Johnson 1974 70hp water pump paranoia

You have a warning horn, make sure it works. With the key on (not start) ground the heat sensor (on head) to ground. The horn should go off.

Re: Johnson 1974 70hp water pump paranoia

Thanks for all the suggestions! I have some good news. I went ahead and pulled the lower unit tonight. I turned the drive shaft and it turned very easy. I also poked a thin straw into the water pump and turned the shaft expecting the rubber impeller fins to hit the straw - and they didn't.

My fear was true - the woodruff key had slipped when I assembled it before. It took me another 7 tries before I learned how to keep it in place while sliding the pump down and seated. So lesson learned, you can't just slide the housing down and assume the key stayed in place. Plus, I should have been able to tell that the shaft turned to easily. Now to turn it you really have to get a good grip and turn it clockwise - because it is turning the impeller now.

One concern is the fact that I had used sealing compound in addition to the gaskets before. I had to scrape all that off when I reassembled. I tried putting new on and since it took me 7 times, it became a mess so I cleaned it all off and decided - heck with it - I'm not using sealing compound. I just screwed the housing down good and snug onto the gaskets. Is that going to be ok? My original pump didn't have any compound, it was just housing onto gaskets.

It won't be until Thursday or Friday before I can re-assemble and hook up the muffs. Hopefully we have cooling and water stream.

It looks like this weekend (if the wind is blowing 35mph in Kansas like it typically does in the fall), I might be able to hit the lake for the first time in 5 or 6 years.

Thanks for the suggestions - I don't know what I would do without forums of people who have been through it already.

Re: Johnson 1974 70hp water pump paranoia

Should be OK, I never use sealer when I replace an impeller.

Re: Johnson 1974 70hp water pump paranoia

Yeah. It just has to hold enough pressure to pump the water up the tube. A little bit of leaking is okay as long as it doesn't adversely effect the water pressure. A tell-tale is essentially a leak in the water jacket too. So, a little water leaks into . . . some more water.

Re: Johnson 1974 70hp water pump paranoia

The impellers are very high capacity pumps. I have never used sealer unless I saw obvious evidence of corrosion..

The key should not be that difficult. I usually seat the impeller on the bottom surface and turn the housing to match it.

Re: Johnson 1974 70hp water pump paranoia

Short version, if You have the 70HP Seahorse, looking at the engine from the side (either) look at the lower unit, You have two horizontal "Fins" just above the prop. Beneath the lower fin, is where the muffs are placed. Between the two fins, there are a series of 6 holes, this is the outflow for the coolant system. If, when you start that bad boy, if you don't have a good flow (not dripping out, but under pressure), then shut it down! Because it only takes a minute to smoke a water impeller, if it isn't already gone. Don't stop there, if it is (and I hope so for your sake) water flowing from these ports, check it! fell it with your hand (don't worry, you'll know when it's too HOT!). And it seems to be comparable to houshold plumbing as far as temp. Just make sure that A)You have the muffs attached, and muffs on, water on. B)that it is FLOWING out of the ports. C)there are no smells (like burning) or smoking (and NO steam comming from the ports. You're "Good-to-Go"!

Re: Johnson 1974 70hp water pump paranoia

Funny, years ago, I used to hunt every year then I stayed out of the woods for a number of years. I knew the exact number of years by the age of my daughter. Now she's old enough to join me.

Lucky for me or unlucky my key is stuck in the driveshaft. I remove the shaft to remove the impeller plate (to get it past the key). I think I read later in the manual it said NOT to remove driveshaft from lower unit or risk losing the alignment and having to dissasemble the lower unit to realign and assemble.

My 76 35 hp Johnson has a thermostat that needs the thermostat o open for water to stream out of the exhaust relief. The manual calls for a 146deg stat that I recently replaced and did the hot water test to check. The range they have for normal operation is over 125deg but not over 163deg. I also have a 75 40 hp rude that has no thermostat.