Enlighten me on the Mocal tstat for a 6 Options

[nditiz1]

So I am planning to install a front oil cooler on my 6 conversion. Originally I was going to use a stock t-stat, but it's a little bulky. So the Mocal was chosen. Before I install this piece that is used by many, I question its existence. Both in and out tunnels have full pass through. When temp goes up, it opens the additional center tunnel connecting the two. If the car is cold and this is installed the oil goes to the external oil cooler. If the car is cold and there is no tstat inline the oil goes to the external oil cooler. At least with the stock one the oil would only go to the cooler when temps reached 185. So educate me on why it is needed again.

[Steve]

Up to around 180 degrees the oil is kept local to the motor. Without it the motor would take longer to warm up and the high cold oil pressure is hard on the external cooler.
http://www.914world.com/bbs2/index.php?aut...;showentry=2867

[nditiz1]

How does the way this works keep the oil local to the motor when oil flows into the cooler hot or cold?

[lesorubcheek]

How does the way this works keep the oil local to the motor when oil flows into the cooler hot or cold?

The little I've read about the Mocal is the center bypass is actually open when it's cold. This would mean that as the pressurized oil enters the thermostat from the engine, it has a free path to the other 3 openings (oil cooler inlet, oil cooler outlet, and return to engine or tank for a 6). Since there's pretty close to equal resistance on both the oil inlet and oil outlet side connected to the cooler, there won't be significant flow there. The oil will take the path of least resistance and go to the return outlet. Then as the oil heats, the center bypass starts to close which will cause less resistance to the straight through path, so more will start flowing to the cooler. When the center closes completely, all the oil will go to the cooler outlet of the thermostat.

I don't have one yet, so take this with a grain of salt, but I was planning to go with one also. Interested in what you find out.

Dan

[mepstein]

I have one. It was really crusty when I got it so I hit it with the vapor blaster. Now it's pretty but I have to open it up to clean it out. I'll take pics.

[Steve]

How does the way this works keep the oil local to the motor when oil flows into the cooler hot or cold?

The little I've read about the Mocal is the center bypass is actually open when it's cold. This would mean that as the pressurized oil enters the thermostat from the engine, it has a free path to the other 3 openings (oil cooler inlet, oil cooler outlet, and return to engine or tank for a 6). Since there's pretty close to equal resistance on both the oil inlet and oil outlet side connected to the cooler, there won't be significant flow there. The oil will take the path of least resistance and go to the return outlet. Then as the oil heats, the center bypass starts to close which will cause less resistance to the straight through path, so more will start flowing to the cooler. When the center closes completely, all the oil will go to the cooler outlet of the thermostat.

I don't have one yet, so take this with a grain of salt, but I was planning to go with one also. Interested in what you find out.

Dan

I mounted mine on the firewall. From engine is from the engine return line. To engine is to the oil tank. The cooler lines are to the front oil cooler. When cold, no oil goes to the front oil cooler.
It’s been set up like this since the late 80’s with a 2.7 and a 3.2 the last 22 years.

[nditiz1]

Dan, that explanation makes more sense about what is taking place. Also seems like dark magic.

So my first picture would be when hot. This picture would be when cold.

[Steve]

You can see in this picture how it’s connected.

[Retroracer]

Another point to note on the mounting, is that the thermostat is making cooling decisions based on engine need/load, so its input (ie. the feed from the engine) should be short in order for it to make those decisions in a timely manner.

Also, think of cold starts; when the cooler is out of circuit, the scavenge pump is pushing barely warm oil back into the external tank; the longer the "engine > Tstat > oil tank" loop is, the more loading the scavenge pumps faces.

I have seen a number of remote oil cooler implementations with the MoCal located at the front of the car; not convinced these were well thought out. Look at where the Tstat sits on factory 911 models with remote oil coolers - close to the tank & engine.

My 2c,

- Tony

[SirAndy]

How does the way this works keep the oil local to the motor when oil flows into the cooler hot or cold?

Path of least resistance. Until you reach operating temp, the bypass offers much less resistance than trying to push cold oil through the narrow passages in the cooler.
(IMG:style_emoticons/default/shades.gif)

[nditiz1]

Another point to note on the mounting, is that the thermostat is making cooling decisions based on engine need/load, so its input (ie. the feed from the engine) should be short in order for it to make those decisions in a timely manner.

Also, think of cold starts; when the cooler is out of circuit, the scavenge pump is pushing barely warm oil back into the external tank; the longer the "engine > Tstat > oil tank" loop is, the more loading the scavenge pumps faces.

I have seen a number of remote oil cooler implementations with the MoCal located at the front of the car; not convinced these were well thought out. Look at where the Tstat sits on factory 911 models with remote oil coolers - close to the tank & engine.

My 2c,

- Tony

Thanks Tony, for ease I was going to mount it in the trunk but after your statement I will make the loop in the engine bay.

Makes sense Andy, I didn't think about cold oil sitting and having narrow passages causing more force to be applied.

[stownsen914]

It's what Andy said. When cold and the center passage is open, oil will take the shorter path. A little oil may still flow to the cooler, but that's fine. When I first looked at one I found it a confusing how it could work since there's no hard shut off of the "warm" path, but the above is what the Mocal techs told me. I've been using Mocal thermostats for years and have been happy with them.

[NARP74]

Mine is mounted in the front right fender well. I have also seen the in the right rear fender area.