Cooling problem with Johnson 200

[karlschneider]

Mystery cooling problem. I looked through the threads but didn't see this exact problem discussed, and I am baffled.
78 Johnson 200 V6 Seahorse

Was running fine but lower unit got damaged, the nut on the bottom of the driveshaft backed off and damaged gears & clutch. Expensive to repair - I found a good used LU same exact model for $100. Did not dismantle (it shifted fine) but replaced the water pump, shift rod seals etc. (stuff accessible from the top)

Installed the LU and it shifted fine, engine ran good but noticed NO water from telltale! Shut down, brought home, ran a wire into the telltale & started with muffs...got a good stream from TT.* Figured a dirt dauber plugged it. ? Took back to lake, launched and saw good telltale stream...idled out of the cove (5 minutes or so) and suddenly saw smoke coming out of the cowling and engine stopped. Did not try to restart it yet (this was last night and it's 102 in the shade now, too high to work on it)

* Thinking back, I recall the telltale discharge water was not warm at all, not sure if that means anything.

I guess the first thing is to muff the LU and try to start it...to find out if the engine is seized up/ruined (apparently this rig has no temperature warning horn...we can't seem to find one) but if it will start, I'm not sure where to start troubleshooting...any ideas would be greatly appreciated! I do have a manual (Clymer) which is pretty decent but doesn't seem to be much help in this case.

krs@valornet.com

 

[luckyinkentucky]

Re: Cooling problem with Johnson 200

I would check the condition of the impeller in the water pump housing. If it is cracked or sand scoured in any way I would replace it. Also if it holds it's shape a few minutes after you've removed it ... replace it. Just because you have a tell tale doesn't mean you are getting the complete water pressure you need.

 

[karlschneider]

Re: Cooling problem with Johnson 200

Yeah I definitely will check the impeller...however it is brand new, probably has about 8 minutes of use. Please don't get me wrong here, I believe you about the telltale but if it isn't a good indicator of coolant flow, what is it actually good for?

Thank you for the reply!

 

[mikesea]

Re: Cooling problem with Johnson 200

the tell tale basically tells you the pump is pumping,you could have problems whithin the heads,or the thermostats,could be stuck,there are two located on the top of each head,four screws 7/16 there is also a poppet valve,take the thermo covers and see what you have,you can test the thermos in hot water,put them back and forth cold hot see if you can see they work,also take note to see if there is any corrosion or salt,dont know if its been in salt but salt is tough on engines,you should have a heat horn,usually located in the control box or if dash keyswitch its located around the switch,has a tan and purple wire connected,the tan wire is ground that is sent via the sensors located on each head,if you disconnect the connector at each sensor and with key on,ground the tan wire going in the harness,you should sound horn,if not horn is missing or broke likely,you can remove the thermos to test ,you might also leave the thermo covers off,start engine and let water pour out,for 10 15 seconds,it will flush anything that might be ther and give assurance that pump works,but realize some water will come out due to hose pressure,you can test run with thermos out,some in Fl.here leave them out ,but I usually gut the thermos to allow a little water resistance,not good idea in cold water use,start at thermos,let us know what you find,after that you get into heads,

 

[karlschneider]

Re: Cooling problem with Johnson 200

thank you for replying! It seems unlikely to me the t-stat(s) would just happen to go 'bad' while the LU was off...? Could just ONE stuck cause this much heating? This old boat has been re-wired so many times it's tough to trace anything but I know for certain there is no 'heat horn' anywhere around the controls or key switch. It probably failed (if it was ever there) and got thrown out. I did venture out in the 102 weather long enough to crank the engine briefly...it turns over fine so at least it isn't seized up...I didn't allow it to start, will try that with water muffs later when the sun goes down some. Oh, it hasn't ever run in salt water, FWIW...
Karl

 

[HighTrim]

Re: Cooling problem with Johnson 200

Ive got a pretty similar motor to you, 2 years older. Make sure you retorque all your bolts after heating up like that. If you dont have the torque numbers, i can send them to you. The water for engine cooling is supplied by a two stage pump containing the impeller. At low speeds, the pump operates as a full displacement pump. At high speeds, the impeller blades bend back under the increased water pressure and the pumpo becomes a centrifugal action pump. You did say however that the impeller was brand new along with the water pump, so you could probably rule that out. Was the impeller key installed snugly? Did you ensure the rubber grommet on top of the impeller housing slid nicely over the copper water tube, my previous owner had overheating due to the grommet shoved in the impeller housing, thats how i found it. If you remove the lu again, run a water line or garden hose up from the copper line, removing the tstats, allowing any gunk that you shoved down with the wire to exit freely. Check the condition of the t stats and pressure valves while ur there. When the power head reaches 145 deg F, the tstats open, allowing heated water to pass through the water discharge. More engine speed opens the relief valves, bypassing the tstats allowing engine to run cooler at higher speeds. But you say you never got out of idle, so id look into the tstats, they should have opened after the 5 minutes getting out of your cove. Finally, i would reccomend testing your temp switches so this doesnt happen again. use a test light to check the contacts and a thermometer to check oil temp, the contacts should close at 211 + - 6 deg and open at 175 + - 7 deg. To see if they work at all though first, ground them out as described.

 

[mikesea]

Re: Cooling problem with Johnson 200

just wondering if the smoke was smoke from a fried rectifier,perhaps its not a cooling problem ,but an electrical fire,you say the wiring is?????just a tought,and yes,one thermo stuck could cause one side to get excessivly hot

 

[karlschneider]

Re: Cooling problem with Johnson 200

Okay, I assume you mean the cyl head bolts, I can do that, the torque numbers are in my manual. I'm beginning to think (without really doing any mechanical work...just mentally going over it) I might have overlooked something in the water pump itself. Is it possible for the riser tube (pipe) to not properly seat up inside the tailpiece? Pretty sure I'll need to drop the LU in any case because I don't believe whatever's wrong will fix itself. Not sure what the "pressure valves" are...I know where the thermostats are installed but don't recall seeing or reading about those valves...?

As for testing the temp switches, I can do that easily but they won't do much unless I wire in some kind of audible device. I have some 12 volt 'beepers' around that would do the trick if I can remember where I put them. I'm a pretty good auto and airplane mechanic but NOT any kind of outboard expert.

I'll double check the impeller drive key and the grommet too. I almost have to believe this problem is due to something I did in swapping out the LU because it only started then. Thanks!
Karl

 

[HighTrim]

Re: Cooling problem with Johnson 200

To test the rectifier.....

Place meter in Hi ohms position

1. Disconnect rectifier lead from terminal block. Connect one ohmmeter lead to either yellow or yellow grey rectifier lead, and other meter lead to ground. Note reading

2. Reverse leads, and note reading. Infinite or very high reading in both checks indicates diode open. zero reading in both checks indicates diode is shorted. Normal diode will show a reading in one direction and no reading in other.

3. Repeat with other rectifier yellow lead.

4. Repeat test, connect meter between rectifier yellow lead and rect red/purple lead. Between yellow/gray stripe rectifier lead and rect red/purple lead.

 

[HighTrim]

Re: Cooling problem with Johnson 200

yes the riser tube (water line) was what i was talking about when i said the rubber grommet on top if the impeller housing. When you slide the lower unit back on, you have to make sure that the copper water line slides nicely into that rubber grommet, that is how the water makes it to the tstats and head, this may be your problem as you only encountered this problem after you changed the lu. The pressure valves are directly below the t stats , you will see them when you take the cover off, they have a large spring on them, not much to them at all. The t stats aren't too much, i actually just did mine last week, about 30 bucks each if i remember correctly, and it only takes about 20 minutes to do both. Make sure you get new gaskets for them, as when you take the cover off you will damage the old one, clean the surface , then apply the new one with gasket sealing compound on both sides of the gasket.

 

[karlschneider]

Re: Cooling problem with Johnson 200

just wondering if the smoke was smoke from a fried rectifier,perhaps its not a cooling problem ,but an electrical fire,you say the wiring is?????just a tought,and yes,one thermo stuck could cause one side to get excessivly hot

I did a quick look and didn't see any evidence of fried wiring on the motor. What I meant about the wiring is in the boat itself, not under the engine cowling, that all seems to be original and clean. We actually mostly rewired a lot of the electrical between the battery compartment and the control console, for accessories and like that. The boat is a 22 foot deck boat. But you raise a good point I had not considered! That -could- explain both the smoke AND the engine stopping! I sure will check that!! (I know how to troubleshoot engine electrics)....thanks!
Karl