 MOCAL Thermostat observations., Observations on a new installation. |
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| John |
 Jul 23 2007, 12:52 PM
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member? what's a member?  Group: Members Posts: 3,393 Joined: 30-January 04 From: Evansville, IN (SIRPCA) Member No.: 1,615 Region Association: None  |
While helping to troubleshoot a new project, we were discussing the operation of a MOCAL thermostat installation.
It was always my thoughts that the thermostat was installed to prevent cold oil (high pressure) from bursting the oil cooler. After reviewing the two ways that you can plumb the thermostat I came to the realization that the cooler will always see full system pressure regardless of temperature. On a MOCAL thermostat, all ports are open when the unit is cold. When the unit heats up, the ports on one half are separated from the ports on the other half. When the thermostat is cold and the oil is thick, there is no flow FORCED through the cooler. The path of least resistance would be through the return line back to the tank. As the thermostat heats up, the internal valve closes FORCING oil to travel through the cooler and finally back to the tank. This means that the cooler ALWAYS sees maximum system pressure. The path through the cooler (when cold) requires more force than it would to return to the tank preventing cold oil from being cooled further. I verified this to be the case in both my cars as well. I always thought it odd that you could plumb them as either straight through or crosswise. It makes sense now. So my question is: Why do they market thermostats as a protection for oil coolers? |
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| flesburg |
Jul 24 2007, 10:42 PM
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Senior Member Group: Members Posts: 506 Joined: 22-November 04 From: Pontiac, IL Member No.: 3,162 |
John,
I think all of our thinking was/is wrong. The scavaging (spelling) pump on a 911 engine does not pump oil at very high pressure on its way from the engine to the external cooler, the filter and then the tank. I do not know where to find out what pressure it is forcing through the cooler, but probably not very high. So it probably would not blow a cooler even when cold. The thermostat is probably there to circulate the cold oil to the tank until it is up to 180 degrees, without the cooler having any effect on its temperature. Possible we could save some weight by removing the thermostat, since we do not start the engine when the oil is below 40 or so degrees anyway. The high pressure pump in for internal pressure inside the engine and does run quite high pressure when the oil is cold (90 pounds or more). |
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Posts in this topic
John MOCAL Thermostat observations. Jul 23 2007, 12:52 PM
904svo Here's the page from Porsche 914 manual about ... Jul 23 2007, 01:58 PM maf914 Interesting question.
I would guess that when the... Jul 23 2007, 02:02 PM PRS914-6 John, you hit the nail on the head. Some thermost... Jul 23 2007, 02:07 PM John In the cases I was investigating, the systems were... Jul 23 2007, 02:49 PM
Steve Thacker I know someone here on the site had posted a pictu... Jul 25 2007, 01:31 PM |
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