Here's whats going on. I've got a pair of 1989 Johnsons 25" Shafts, ones counter rotating, 140hp, in near ment condition, Absolutely no salt water corrosion either inside or out. Mounted on an 1990 23ft, walk around cuddy cabin Hydra Sport boat. Each engine has had and always were taken care of to the point that it might be deamed "over kill." SO HERE'S THE PROBLEM, The starboard engine overheats at idle. Port engine, with exactly same maintenance runs at 143-145 no mater what. This is what I've done so far.
1. Replaced water pump impeller
a. used Johnson/Evinrude impeller
b. used Sierra brand impeller
c. used CLM brand impeller
d. Used Pro-marine impeller
2. Replaced water pump housing and glued housing to wear plate
3. Replaced water pump housing without weap hole and glued to wear plate
4. Replace thermostats using both stainless steel and brass styles.
5. Replaced springs for thermostats and base seals.
6. Replaced temp send units, in both heads
7. Replaced temp guage in console
8. Replaced factory sensors in the heads and used external sensors.
9. Replaced heads with later model and all thermostats, springs and hardware associated with thermostats.And all sensors using both internal and external style.
10. Acid vatted block. No scale or obstrustion
11. Filled block and back flushed using 175psi air pressure.
12. Also have streatched the springs in both styles of heads. Then replace them.
This blankety-blankety motor still overheats at idle. Put it up to 1500rpm in gear, cools right down. There are a few other things that I've done also, Like check timing, fatten up the idle jets for more fuel, changed brands of sparkplugs, changed to pure synthecic oil instead of a syn-blend. And Yes have pulled the block off and checked the copper pipe coming from the water pump housing for leaks and/or cracks. Also checked the cylinders for cracks.
Need help! I'm taking the boat to Port A in July and plan a 75mile offshore, overnight trip. I don't need to be broke down out there. So If Anyone can offer a suggestion, or comment, I'd really like to hear it.

[censored] Mike, I read your posts to learn so I sort of hesitant to say anything for fear of insulting your intelligence. But Ill throw a few ideas out.

Have you tried it without thermostats installed? That would provide max flow. Not saying you would run it that way but as a test.

Shorted wires in the harness between motor and console. You've done so much work as it is, it may be worth it to rig this problem child to the other motor's harness and see what happens.

Pop-it valve, I don't know but I've read about it a couple of times on other threads.

Discharge clogged? Water has to be getting in with all the work and replacements you've done, but is is getting out of the motor.

Jtexas mentioned something about a divider plate on a thread but it sounds like you've already been deeper than that.

It ain't much and probably isn't much help. Wish you luck

it seems as if there is a restriction on the outflow side. a very minimal one, that with anythign above 3psi, it opens and flows. is there any way the peehole has something hung up in it? or is it even possible for a kink to be in the outflow side anywhere? maybe a piece of trash floating around in there somewhere.

Mike,

I ran into an Johnson a few months ago, that one of the termostats wasn't put back together right and for some reason it was running hotter at idle that what it should have been. It was only one one bank though. So we took it back apart and found the base seal was put in backwards and for some reason, it didn't want to let the thermostat open all the way and didn't let enough water out at idle. Bring the RPM's up, it would cool back down.

We dropped that lower unit 4-5 times, double checked everything, checked the water tube (didn't go as far as pulling the head), but everything seems AOK. Turned out be one little mistake.

YUP!...I've gutted the thermostats and run it that way.,it will slow the water flow down enough for the heat to transfer from the metal to the water. By doing this I have to take the white/black stripe wire and jump it to ground, as the ignition system is tyed to it and the sensor tells the ignition to advance or retard. I don't like doing this for 2 reasons. 1. I'm not maintaining the correct temp in the block and the pistons are hot and swollen causing less clearance in the piston to cylinder. and By doing this I'm prematurely wearing out my cylinders. 2. It makes the ignition do weird things unless I ground the sensor. Popet Valve: The J/E have high by pass springs on the thermostats that act like popet valves in a Merc. Yea. Stretched, shortened, and replaced, (actually replaced twice). Divider Plates (actutally Divider Tubes): The looper style engines do not use them, only crossflows do. As far as water getting out, there is no obstruction in the block or exhaust, it will freeflow. I don't know of any thing that might be in the wiring system that would cause it to blow the horn or show at the same time a rise in temp on the guage. I can however unplug port and plug it in to starboard with no problem, I will try that and see what happens. I really appreciate the thoughts........mike

Michael. I changed from the vernatherm/diaphram style thermostats to different heads that use the double spring vernatherms. I'm wondering about the hole that is in the exhaust shoe, (the piece between the exhaust down spout and the lower unit, right behind the water pump housing) If it has anything to do with building water pressure in the block?

I for the life of me can't find any restriction in the water system anywhere.

Okay, I'll say it and risk Mike sending over a hit man to find me. You are 100% certain the key way is inserted and the impeller is engaged on the key?

Dont laugh, I installed one of those plastic ones backwards once, while in a hurry. Had to swap it out at the ramp.

But that isnt it...it would overheat at higher RPMs too, if that were the case.

Sounds like a water tube grommet lodged up there somewhere?

maybe the prop is messed up?? Just kiddin'

man i feel for ya Mike. that be why i never wanted to be a mechanic.

i wish ya the best in finding your problem.

Hmmm... Could it be the heads have a different shape and for some reason aren't letting the water pressure open the T-stats until the RPM's are raised?

This one is beyond me.

Is the pee stream extremely strong? Normal?

Where are you getting your reading, do you have seperate gages for both motors? Have you tested your gauge to see if it's giving you an accurate reading? I know it sounds silly, but I'm just trying to throw something at ya....

poboy might be on to something, have ya put a temp gun or thermomelt on it?

Where is the indicator outlet on that model? Is it at the top of the head, or near the bottom?

If it's at the bottom, try re-routing the hose up and over the head and back down to the outlet, to purge air from the water jacket.

Best investment I ever made was my laser Temp Gun. Takes all the guess work out of it.

$70 bucks!

These engines are set up with two temp sending units (factory) one in each head. I have also installed an external, aftermarket style on each head and replaced the normal hot-cold outboard temp guage with an inboard/outboard temp guage that reads actual degrees. The hot heat horn is also hooked., I have'nt shot the block with a temp gun or used a thermomelt stick, but I can say for sure ole' mr. hand can tell for sure it's hot. I've even tried relocating the external temp senders from top-middle-bottom of each head and I'm able to swap the sending leads from one head to another. At any one time I can take 4 separate temp reading thru the guage and have swapped guages from one engine to another, All reads will be almost exactly the same at any one time. As far as the heads go, the only difference between them is that one is machined deeper to accept the different sytle of thermostat. I measured the volume of water passage in the orginal and then the other style that I replaced the orginal with. both measured the same. I also measured the combustion dome and both were the same, I also measured each for warpage. No warpage/........

Never messed with a counter rotating unit, wouldn't the water pump housing be different and the possibility exist that the housing is cut differently? That is a long winded way of asking if the right parts are installed, the impellor should be the same.

rings?

The only difference with a CR is the lower unit gearing for the counter rotation. Any standard motor can be made into a CR with a CR lower unit.

This problem may have a simple solution, Mike. Usually, when I run across something that seems to defy all logic....it's a small item or oversight that's right under my nose...or something seemingly insignificant at the time.

Waterpump housing, running lean, gasket out of place...or something.

"...This blankety-blankety motor still overheats at idle. Put it up to 1500rpm in gear, cools right down. ..."

The RPMs have to be significant here. What's the difference in 850 or so and 1500 ? More water PRESSURE. Water being sucked in thru the inlets at a faster rate, too.

I know it sounds elementary. I'd check for problems BELOW the waterpump.

Also, it may be starving for fuel/lubrication at idle.

Mike,
What about timing and reed box? Ignition at the wrong time can really heat up an engine. Also if for some reason the exhaust is not being completely pushed out after ignition that is another possible cause.

I know these have nothing to do with the cooling system, but from what you posted, I'm trying to think outside the cooling system.

Cut the problem in half. Swap lower units with the other engine.
If the same powerhead overheats, then you know it's up top. If not...then of course, it's in the lower unit.

Pain in the rear, I know. But it might cut down the size of the search area.

did you put the rubber seals in the top of the cap where the pick up tube is inserted without these or if the old ones are damaged you loose a lot of flow

Still curious as to what the problem was, Mike.

Did you replace the water diversion tubes that go between the cylinders? Have seen them cause overheating when they shrink so much they wont direct the water flow correctly.

I've never checked the timing, mainly because the engine is still running the "from the factory" ignition system, fact is both are still running the same factory ignition system. I have'nt swapped lower units, that very well might be worth the effort. I'll be installing new a water pump housing, complete with seals, impeller, grommets, etc,etc,etc/ Hopefully this week. I already addressed the diverter tubes, Loopers don't use them.
If this doesn't work; I'm going to tear the engine completely apart, right down to its crank bearings, check everything, recheck everything, and if it even looks like it's not brand NEW, I'm going to replace it. I'll even acid wash the entire cooling system just to make sure that there is no scale/obstruction. If that don't work. I've really been wanting a pair of counter rotating 4 strokes...