1982 JOHNSON 175 TEMP ISSUES

[Shadowdrifter]

I have a 1982 Johnson 175hp (J175TLCNB) on the back of my 19 foot bass boat and while idling, trolling, or below approximately 60% throttle it runs like a top. there is however a significant temperature difference between the top cylinders on each side and the bottom, the top cylinders usually run between 145-155 F and the bottom two cylinders run about 117-130 F (both depending on water temperature) the motor does not have thermostats in either head the previous owner removed them. After much investigation and watching it closely I have established the temp ranges to be regular the way it is. the problem comes in a WOT or really any throttle amount above ~60-65% I start getting the endless BEEEP that is from what I understand a overheat alarm, from what I have noticed the alarm comes on when the motor is around 170-175 F on either of the top two cylinders and stays on until the cylinders cool to approximately ~160 F (at this time the lower cylinders all stay below 140 F).. The hottest the motor has ever gotten is around ~184-187 F.

what I have looked into so far is fuel mixture on the top carbs, and I have checked my plugs for any obvious issue signs. I have not yet torn into the motor.

Does anyone know what the actual run temp of the motor is supposed to be and at what temp the alarm should be sounding is there a possibility I could have something faulty in the alarm system?

 

[emdsapmgr]

That engine should be running thermostats for even cooling throughout the block when planning and at idle. Your engine at idle should be between 143 and 155 when warmed up. As much as 20 degrees or more COOLER at planning speeds, when the thermostat pressure relief valves open up. (also part of the thermostat cooling system.) You will get a hot horn when the engine heats up to 212 degrees. The hot horn will silence when the engine cools back down to 175-still way to hot for normal operation. Are your temp readings from a laser temp gun? If so, you need some action quickly, as I would not run this engine (other than testing) till your overheat issues are resolved. First of all, put the stats and pressure relief valves back in each thermostat housing. Run it and see what happens. If it still overheats, pull the head covers off both heads and see what the cooling passages look like inside the head. If they are clogged with debris, that's a sign of what is inside the block. If they are clear, then pull the heads and check the rubber water diverters by each cylinder liner. If they are out of position, they could be blocking water flow in the power head. I'll attach a picture of what the correct position is on a water diverter. The on left center of the pic is correct. The one on the right is an example of one which is out of position and likely is disrupting water flow. Notice the water jacket areas are really clean of debris. The fact that the upper cyls are running much hotter than the lower cyl is not a good sign. Possible the block may not be filling fully with water from the impeller. You've not mentioned that the impeller is new. A most critical part of the cooling system. Should pump 6-7 lbs or more at idle, up to 18-20 lbs at WOT.

 

[Shadowdrifter]

Supposedly the PO ( I bought the boat mid last summer) had just replaced the impeller about a month before I purchased it, he showed me the old one. Either way I think I am going to go ahead and open it up again just to insure it is functioning properly and installed correctly, as I noticed the other night when running on the muffs at idle, with my brother in-laws boat side by side, the tale tell on mine was strong but not near what his what and I also had less water exhausting at the prop. after posting this I was doing some more looking and found the post about the how to on replacing an impeller and some of those symptoms were very similar to mine, as well as what you said about the block not filling all the way. Also I pulled the head covers at the end of last season to see if there might have been a blockage and they were both spotless clean as well as the water jackets behind where the thermostats should be, I did not pull the heads at that time though as I do not have a service manual yet, and didn't want to attack things before necessary. Yes I was using a hand held IR temp gun, I definitely wont be running the boat this year until its reconciled though, I am trying to get a jump on getting ready for spring crappie and getting this resolved

 

[emdsapmgr]

You seem to be on top of this problem. Good that the block looks clean and that the head passages were clear. Check the temps after you replace the impeller.
If there is any doubt about the integrity of the impeller housing, you might as well pop for a new one of those too. Plus, replace the stats and pressure relief valves-they act as a restriction, causing the block to fill first- before the cooling water leaves the block and goes down the midsection. If the laser temp readings still look high, I'd still probably pull the heads and visually check the position of the rubber water diverters by each cylinder liner. One other thing. Your telltale nipple exits at the bottom of the outer exhaust housing. I'd probably re-orient the hose barb so it is directed skyward. Get a longer telltale hose and loop it upward to the top of the block, then back down to the telltale nozzle in the lower cowl. That way the water has to fill the block before it goes out the telltale-if it's not this way already. Sometimes those nozzles will fill with crud (sand, weeds, etc.) so you may want to run some weedwhacker line up the nozzle when running to clear it out.

 

[Shadowdrifter]

Ill have to look at the telltale again I don't remember off hand how it is oriented, I do know it is cleaned out though cause I had it off when I removed the head covers to clean it and replace the hose that was starting to crack, but that does make since about routing it up like that before exiting the cowl.. also something else I noticed last nigh while trying to get my gauges (volts, and tach) hooked back up was that I have water leaking from the seam between the mid section and the gear case near where the pomp is, I don't think I ever noticed it before cause its not a horrible leak, its just a small one but either way I am pretty sure its not supposed to exhaust water there, and my muffs themselves normally spray water into that area so I haven't seen it till now. so now the lower unit is definitely coming off this weekend for further investigation and potential repair. on a side note, do I have to remove the prop to pull the lower end or does it just make accessing the bolt under the skag easier

 

[emdsapmgr]

The water coming out from the seam between the midsection and the lower unit is normal. There is no factory seal at that seam.

 

[Shadowdrifter]

No Title

How does it get out of the pump housing and exhaust cavity though, from what I can tell looking at both of the parts diagrams for the gear case and exhaust housing both of those water passages are sealed internally there at the split. i'm not trying to argue just to understand this is my first boat and i'm very mechanically inclined im just not overly familiar with boat motors. I have marked the two lines in red on this photo where I am getting the water from (this isn't my motor but it is one similar in design. It just seems to me that like you said if the motor is not fully filling with water that loosing gpm and pressure right off of the top at the pump like that could potentially be a cause for that?. But again that is why I am asking before I just start tearing my motor down.