Running T-Stats VS No T-Stats

Blu_Lunch · #1 09-08-2009, 02:19 PM

After starting the thread about T-stats, there was talk about running/not running T-stats I ran across this it make a ton of sense.

1) A outboard motor does not warm up very fast if at all at an idle in cold water.
2)Thermostats can only help it warm up so fast if you have 40 +/- deg. water running through your power head.
So how do you run a Opti or other outboard under these conditions?
1) Idle at least 3-4 minutes minimum.
2) Take off easy.....Do NOT hammer down from an idle while still cold. Take it easy for a ways. Increase the RPM's gradual.
3) Make sure your thermostats are working properly!
* This one is very important ... (I had this happen to me) I was running a 2004 225 Opti in 40 deg. water, motor was running at 130 deg range it picked up a pebble and stuck it in a thermostat (held it open) I had Smart Craft gauges and always have it on eng. temp in cold weather/water..
When the thermostat got stuck open it cooled the motor down to less than 80 degrees!...It would NOT go above 80 degrees even at WOT!
So what's the problem??
First you have a certain amount of clearance between the piston and cylinder wall.
example... cyl bore on a 200/225 Opti is 3.6265 in. (std.) The piston has approx. dia. of 3.6210... So you have approx. .0055 piston to cylinder wall clearance...
Now when a motor heats up it expands...So when it's up to normal operating temp. the piston and cylinder wall are both a larger diameter.
When you run a cold motor hard or up to WOT real quick what happens is the piston gets hot much faster than a cylinder wall that has cold water against the outside of it....The hot piston expands but the cylinder wall hasn't yet....What happens from there is called a Cold Seize.. The expanded piston don't have the .0055 clearance needed and it will seize or stick to the cylinder wall. If it seizes/sticks running @ 5500 RPM + it just rips the wrist pin/connecting rod right out of the piston...The connecting rod will go out of control and end up out through the side of the block...At this point the power head is destroyed...This is one of biggest failure issue of a Optimax and one that can be avoided by just following the above info. by making sure it warms up and has time to warm up right ........

THEFERMANATOR · #2 09-08-2009, 02:38 PM

Also to add onto this, ALL loopers are pretty inefficient at low RPM's. All of your modern 2 strokes since the middle 80's are loopers as well. The inefficiency of a looper at low RPM's results in a very poor burn at idle and alot of fuel going out the exhaust unburned. This is one of the reasons for some outboards having the very black prop hubs and an oil line on the midsection. Also the incomplete burn at idle creates alot of thick wet pasty carbon build-up. At low RPM's this build-up ends up in the piston rings and exhaust chest rather than going out the exhaust. Eventually this can lead to sticking rings, spark knock under load, and the all time favorite of a seized piston which can just shut it down or cause a spectaculiar show of rods flying out the side of the block. Loopers need to be at roughly 130-160 degrees at idle in order to burn the fuel mixture even remotely thoroughly, but they need to run around the 110-125 mark under a load to prevent the pistons from sticking in the sleeves.

2 strokes create alot of concentrated heat inside of the combustion chambers due to the flame following the airflow through the chamber. The piston to cylinder clearance on average will be .002.006 at the bottom of the piston skirt, but will have clearances upwards ot .010-.014 at the top of the piston where the flame front hits. This is to allow enough expansion room to keep the piston from seizing under a hard run. Well at low RPM's the temps are not there to create the expansion in the pistons and this is why you get the all famous slapping sound when cold. If you run without T-stats you will have that extra clearance there all of the time instead of just for a few minutes and over time this will result in a hammering effect on the pistons and cylinders and eventually wear the components out.

There are so many reasons to keep thermostats that it still baffles me how the thinking from 80 years ago still prevails. When t-stats first came out they did give problems, but just like carbs, fuel injection, and electronic ignitions the bugs have pretty well been ironed out. The pros far outweigh the cons to run T-stats, but it's your money.

phatdaddy · #3 09-08-2009, 05:59 PM

i change t-stats once a year with the water pump change, and i have found out it is wise to temp check them be for install. i drop them in a pot of boiling water and when they open, insert a piece of fishing line, let them cool and "clamp" the line. let the water cool to room temp and suspend the t-stats in the water( i tie them to a wooden spoon). start heating the water and note what temp they start to drop off. it is amazing sometimes at the difference. a laser thermometer is very helpful in the test...

macojoe · #4 09-08-2009, 06:16 PM

My merc runs hot all the time, it always smoke from the heat, man if you hold your hand in the water it will burn a hole in it!!
BS said this is normal for them?? That you will foul plugs if you no run T stats??
Well it scares the crap out of me so I took the T stats out for the summer,(water temp mid 60's) I will reinstall for the colder months, But motor still smokes and runs warm now not hot, and I have no temp gauge so not sure were its at. But plugs are good and motor runs great all the time, i just let it run a bit before I take off.

THEFERMANATOR · #5 09-08-2009, 10:05 PM

Quote:

Originally Posted by macojoe

My merc runs hot all the time, it always smoke from the heat, man if you hold your hand in the water it will burn a hole in it!!
BS said this is normal for them?? That you will foul plugs if you no run T stats??
Well it scares the crap out of me so I took the T stats out for the summer,(water temp mid 60's) I will reinstall for the colder months, But motor still smokes and runs warm now not hot, and I have no temp gauge so not sure were its at. But plugs are good and motor runs great all the time, i just let it run a bit before I take off.

Your playing a DANGEROUS game MJ. Mercs cooling system is designed to have the t-stats in not only to maintain the temp but to restrict flow through that area. Without them in there the poppet valve won't open and this WILL cause hot spots in portions of the block. Removing the t-stats in many engines(not just outboards) WILL cause overheating and blown headgaskets.

Blu_Lunch · #6 09-08-2009, 10:39 PM

Quote:

Originally Posted by macojoe

My merc runs hot all the time, it always smoke from the heat, man if you hold your hand in the water it will burn a hole in it!!
BS said this is normal for them?? That you will foul plugs if you no run T stats??
Well it scares the crap out of me so I took the T stats out for the summer,(water temp mid 60's) I will reinstall for the colder months, But motor still smokes and runs warm now not hot, and I have no temp gauge so not sure were its at. But plugs are good and motor runs great all the time, i just let it run a bit before I take off.

My Mercury telltale is very hot also but today I bought a IR thermometer, ran it around the lake a few times at 4600 rpm stopped the boat put it in neutral popped the cover open and the head temperature was 148.2 and 147.9. I'll tell you I put new T Stats Saturday and it idles better than before, real smooth........

macojoe · #7 09-09-2009, 10:27 AM

but its so hot it scares me!! i guess i will have to get a temp gauge and watch it

THEFERMANATOR · #8 09-09-2009, 11:39 AM

Quote:

Originally Posted by macojoe

but its so hot it scares me!! i guess i will have to get a temp gauge and watch it

Anything over about 120-125 degrees will make a lot of steam and feel unbelieveably hot. Loopers need to reach at least 125 in order to idle somewhat cleanly, and 140-160 is normally better for idling.