98 johnson 90hp crossflow has me stumped, again...

[bwilson2626]

Ok.. so I replaced both thermo's, impellar assy, & water diverters, has strong weep flow. But.... overheats after initial start up, on the water. Wont overheat with muffs at home. Then after a minute or 2 at cruising speed, cools to normal & stays cool while running or at extended idle ( in gear or not ).. but leave it shut off for an hour or so, and it will overheat again st restart..

Any ideas?? Ever heard of any-such a thing?? Im frikkin lost

 

[interalian]

Bleed holes in thermostat plate clear? You can test by putting your finger on the thermostat housing when it's overheating. If it's a lot cooler than the heads, you're not getting flow through, and the stats aren't opening because they're not getting warm.

Once you've increased the speed, the poppets open and cooling water will flow. I suspect that when you're running on muffs, there's enough pressure to push the poppets open.

 

[Faztbullet]

"P" flow has nothing to do with engine cooling... it just to tells you impeller is pumping

 

[schematic]

how soon after start up does the alarm blow? Is it possible its not overheating? Did you confirm hot engine? Did you eliminate OMS/VRO pump alarm?

 

[bwilson2626]

Sorry so long getting back, busy season at work had me bowed up.
Anyways, Engine is definately overheating. removed the thermo housing today to inspect, found nothing out of ordinary. reassembled and has same issue. 8 minutes into idle, overheat alarm activated. Lazer temp gun read between 195 & 203 on heads & exhaust cover plate. The thermo housing read 87. Thats when the weep began sputtering out steam.

Interalien, what are the "bleed holes " you referred to? The thermo housing is very clean.

Can I remove the 2 hoses connecting the head ports to the thermo housing and run for just a bit to test for flow from the heads?
Since I had the thermostats out, I tested them in hot water, both opened at about 145. I ASSume that is about right, but not 100% sure.

 

[interalian]

There are two tiny holes in the thermostat spacer plate, about 1/16" diameter. If they're plugged with anything, hot water won't get past the thermostats and heat them to make them open. Look for these holes inside a slot that's about 1/2" wide.

You can take the hoses off the bottom of the heads to test - you should get lots of water from these at idle. Remember: the thermostats are the LAST point in the water flow before it's dumped down the leg.

 

[interalian]

[No message]

 

[oldboat1]

If it's fine with hose water pressure, but not in the water, it sounds like the new water pump might not be doing its job.

 

[bwilson2626]

Hmm. Is there a way to test if i have enough flow from the pump?

 

[oldboat1]

Guess the easiest test is to run it in a large trashcan, water 6 inches or so above the intake. Can safely run only at idle or high idle, but see if it overheats. If it starts to overheat (pretty much anything close to 160F), drop the l.u. and check the water pump assembly (Check against a parts diagram).

 

[bwilson2626]

Ok, Interalien, my spacer plate only has 1 hole ( 1/16" i.d. towards thermo housing, about 3/16" i.d. towards motor ), and it was clogged w a near microscopic piece of debris. If that 1/16" hole being clogged can be detrimental to the cooling of the motor, I would enjoy a chat w the engineer who designed it. I cleared the clog & reassembled the thermo assy.
Oldboat1, I dropped the lower unit, disassembled and inspected the pump, with no corrections.
But reading what both of you wrote, it started to make sense. So before reassembly, I cut the fitting off my garden hose and slid it over the water tube leading to the block and flushed it. After turning on the water, there was a long ( 30 second) time before the water came rushing out of the head outlets. Immediately made me think something just became dislodged, and now the water flowed freely.
Long winded, I know, but I wanted to explain best I could.
Reassembled everything and it runs perfect. Not absolutely sure what the issue was, but the weep flow is noticably stronger now, and the running temps are 135ish, ( i.r. lazered on heads).
I did the work, but without you guys volunteering to take the time to read & respond with your insight from experience, I would likely be taking my motor to the shop.

Dearly appreciate your time and willingness to help. SALUT!

 

[interalian]

Glad you got it sorted. That bleed hole is an interesting design, no? I think a better solution would have been small slots on the sides of the poppet valves, and a tougher (than rubber) sealing surface in the spacer block. That way every time the poppets got forced open at higher speeds, the bleed would be 'cleaned' by passing water.

 

[Fed]

From what I can see your motor has the thermostats at the top of the heads not down below like interalien is talking about.
Are you sure it's a 98?

 

[racerone]

I believe 98 is the last production year of the simple crossflow design.

 

[oldboat1]

kudos on the fix, bwilson. Good boating to you!