Hmmmm...no thermostats after all

[stanggt]

Well I finally got around to changing out the thermostats and all the other related parts today.  Once I got the cover off to my surprise there were no thermostats installed after all.  I don't know if this has been causing my engine to go into SLOW mode but maybe by putting new ones in it will at least help.  I have a few days to clean as all the parts have not arrived yet.

As long as I have the engine down for repair I am also rebuilding the carbs.  I already have them off and on the workbench.  I will disassemble/clean/reassemble tomorrow.

[kraw2]

Without the TS's the engine will overheat. More then likely that was the problem.

[SaltH2OHokie]

Without the TS's the engine will overheat. More then likely that was the problem.

Actually, the opposite is true. If anything, it runs below optimum operating temp with no thermostat.

[Capt. Bob]

Without the TS's the engine will overheat. More then likely that was the problem.

Actually, the opposite is true. If anything, it runs below optimum operating temp with no thermostat.

Yes and no.

At start up, the engine will take longer to reach optimum temperature of operation (if ever) but under high speeds (think WOT) the water passes through the block with less restriction and higher speed. It (the water) loses ability to effectively transfer heat and as such can cause the motor to run at higher than normal temperature. This could and at times does (variable of time and engine rpm) cause overheating.

[GoneFission]

I don't know what kind of motor this is, but if it's a Mercury - it has a complicated cooling system consisting of thermostats, water pump, and a poppet valve that all work together.  It's very reliable when properly installed and maintained.  Sometimes a shade-tree will take the thermostats out thinking the motor will run cooler - but it just does not work that way on a Mercury.  Usually changing the water pump is all you need.  Sometimes the thermostats will gunk up - that's why you need to check them regularly (every year or two, depending on your usage).  Again, some shade-trees remove the thermostats to prevent blockage - but create a new problem trying to solve the old one.    

Also, fuel economy goes way down on a cold motor - you need some cylinder heat to help vaporize the fuel charge.   Put the 'stats back it and let her scream and fly!

[John Jones]

Thermostats gunked up.  Naw!

[stanggt]

The engine is a '98 Johnson 90 V4 90degree crossflow.

[Georgie]

Stan

A bunch of us have the older OMC crossflows while many also have the slighly more powerful and more recently designed loopers.  I have three crossflows (plus enough parts to build a fourth) have built/rebuilt three others, and had been running my personal 115 without 'stats as well based on an experienced friend's advice.  Based on conversation on this thread plus recent advice from my local service shop (whom I trust implicitly btw) I finally got around to installing mine today.  

One point of clarification which you may already know but wasn't stated explicitly in this thread or your prior thread to my recollection:  The "pisser" is only a telltale/indicator to let you know if water is getting through your powerhead.  It can be inoperative due to a small clog and your engine can still be cooling fine.  You need to watch/feel the coolant exiting at the top of your cavitation plate on the lower unit to monitor temperature and volume of water flowing through your engine.

Regardless, pretty sure the guys are correct.  Obviously, 'stats are intended to keep the engine running at the optimal temperature for efficient combustion.  Lack of stats will definitely result in cool running at low idle which correspondingly results in inefficient burn.  Alternatively, absence of thermostats probably also prevents optimal cooling and may potentially result in hot spots in the cylinders at cruising speed or top end because the system isn't pressurizing optimally for balanced heat exchange.  Allowing the coolant to free flow through the system allows gravity to pull the water out of the reticulations faster than intended and doesn't allow the cooling system to properly pressurize which is needed for the water to reach all the nooks and crannies in the cooling jacket and exhaust housing.  Based on my experience, a system without 'stats isn't ever likely to overheat to the point of setting off the alarm, but almost surely doesn't protect your engine as much as it should.  

That  said, not finding thermostats in your engine means that the 'stats weren't the original problem.  

Couple other suggestions based on your prior thread:

1) Optimal RPM for these engines is approximately 5500. (factory manual states 5600 I believe) so based on the 4700-5000 you reported it sounds like you have either a propeller or combustion related issue which is preventing your engine from performing properly.  
2) Also, the same cable runs your throttle when in gear or in neutral, so if it works properly one way, then it probably is working properly in the other unless you have developed some weird binding situation in your controls.  You may need to systematically isolate each separate component of your throttle linkage to find any malfunction here.
3) I don't believe any of the crossflows ever had a SLOW mode so that is probably not the problem, but yours is several generations newer than mine so maybe they found a way to add some electronic protections with the late models.
4) when running properly, the telltale will start "pissing" at least 30 seconds before the coolant starts pouring out at the cavitation plate.
5) I've read that you can rent an infrared heat sensor from many automotive/parts/service shops and shoot the temp at your cooling jackets and cylinder heads between/behind the cylinders if you want to be 100% certain of operating temperature regulation.
6) based on your description of the lower unit, you may have accumulated salt/corrosion/sand inside your cooling jackets which block water flow exactly like a clogged artery blocks blood flow in the body.  That could be your issue and it's a pain to fix b/c the cooling jacket screws snap VERY easily without the propery equipment and torque settings.  Air/vibration tools are a must I've heard.

JJ - that's GROSS.  What were the symptoms leading to the "autopsy"?

[John Jones]

JJ - that's GROSS.  What were the symptoms leading to the "autopsy"?

Actually the motor was doing fine.  I had bought it used and from other things I was seeing pointing to lack of maintenance (like an impeller hard as concrete and worn out spark plugs) I decided to change the thermostat.  I guess I caught it before it did any real damage.  I have posted these pics before but here is what it looked like two years later when flushing with Zep Citrus Degreaser after EVERY trip.

[Capt. Bob]

I don't believe any of the crossflows ever had a SLOW mode so that is probably not the problem, but yours is several generations newer than mine so maybe they found a way to add some electronic protections with the late models.

Not really sure that the induction system had anything to do with a rev limiter (S.L.O.W.) protection system especially in 1998. If you have a factory service manual, I'd guess it would indicate if there were sensors in the heads that would signal the power pac to limit rpm due to excessive heat. If so, maybe a sensor is bad. Did you already check the sensors or was that another thread (gettin' too old to remember).

[stanggt]

Nope, haven't gotten to the sensors yet, though I did locate them and read up on how to test them.  After I get the carbs back on (cleaned and rebuilt) and the t'stats in that is my next "project".  So far I can this engine was poorly maintained.  I might just make a winter project and do a full rebuild.  This will not only ease my mind about reliability, but it will also teach me a lot about outboards.