Pressure or thermal regulation pros:cons

[Gary Allan]

I've was discussing a few things with another member back channel. He was seeking a stand alone pressure relief in sensible pressure ranges for out level of need. He finally found a check valve (sprung ball type) that could have any breaking pressure spring installed from 0-100 PSID. It wasn't cheap (about $40) ..but that's comparable with the Permacool thermostat in price ..and about half the price of a Mocol.

This leads us to our opinion forum of the moment. What's your opinion upone either method for flow regulation in terms of auxilliary coolers and filtration? Each has its advantages and limitations.

I've observed serveral modalities used in OEM installations, mainly Fords. They use a simple sandwich with an internal pressure relief vrey like Permacools. It just sets the max amount of pressure seen across the cooler circuit. Thinner oil ..assumed to be hotter, more flow through the cooler circuit. Simple and reliable. As long as you're using a spec'd visc oil ..and everything stays nice and tidy ..you should have long term reliability and adaptive cooling as needed. The advantage to this setup is that you can dial in your pressure drop/elevation across any downstream add-ons. The disadvantage is that it's numb to anything except pressure.

Thermostats off you the advantage of assuring a given oil temp before you see any additional effects of you add-ons (either cooling or filtration) ..but are totally numb to the pressure drops/elevations that may occur even though you've heated the oil to 180°F. They are numb to anything besides temp.


Anyone have any opinions they would like to share? Things to consider ..compound setups ..and just what does anyone think is a reasonable pressure drop/elevation to tolerate across any add-on???

 

[Mitch Alsup]

I can tell you the my Ferrari F355 uses a thermostatically controled bypass valve on the circuit through the oil radiator/cooler. It starts to open at 140dF and is fully open at 165dF.

I can also tell you that the pressure sending unit is located after the oil filter.

I am not stating any opinion about whether this is better than that.

 

[Shannow]

I'd guess that thermostat is better, but relief is simpler/more reliable.

The relief type setup is passing oil through the cooler all the time regardless.

(I like my toyota's water cooled/heated oil cooler) whichever is the warmest brings the other fluid up quickly. Engine is at operating temp before I leave town (about 2.5-3 miles)

 

[Gary Allan]

I use the coolantil sandwich (DONUT to the UK crowd - don't know about OZ's) type cooler. The only drawback is that you slightly delay the coolant warmup cycle. It is the simplest and most reliable way to regulate oil temp. Luckily, coolant and oil are ideal at like temps.

The relief system, to be close to the same effectiveness, requires a given viscosity to "imply" a given temperature. They really don't put much tension on these relief valves. If they were anywhere near 10 PSID, I'd be surprised. Permacool uses 2 PSID. Any cooler is going to drop a bit more then that with any distance to the lines unless it's relatively low volume. Hence any significant flow is only going to occur under high temp/low visc anyway, or so I reason

 

[427Z06]

Gary, don't live down your Rube Goldberg reputation. Use both pressure AND thermal regulation!!

 

[Gary Allan]

Just what are you trying to say here, pal?? That I could complicate boiling water?? (wait, I think I did that already

)

 

[427Z06]

Seriously, I favor the thermostats since they allow more flow. Also, most allow some flow to the cooler even when they're diverting from it.

 

[Curious Kid]

Gary - In a sense it depends upon what the user feels is best to control as there are variables entailed as you mentioned.

Controlling oil flow through a cooler with a pressure valve assembly would rely on thermal thinning of the oil as you mentioned. This in a sense would be used to "dial-in" a stabilized viscosity (narrowed by the effectiveness of heat rejection), for which the engine was seen to benefit the most. As you also said, such a pressure dependent system is "numb" to temperature in a direct sense, so if a higher viscosity oil was used or the "ideal" grade had thickened, than higher stabilized/regulated temperature levels would be maintained. Worst case, thermal oxidation could lead to thermal runaway. Using a thinner viscosity lubricant would lead to lower regulation temperatures, perhaps over cooling in the sense of not enabling ample time for moisture and fuel evaporating off within the average time of service/start.

A thermally controlled cooling system would better serve in managing oxidation effects of the lubricant, however "numb" as you've said to resulting stabilization in viscosity, which is fine as long as the user is sure to utilize an exceptible viscosity grade. I would think though, as a lubricant approaches operating temperature, that it's decreasing rate of thinning could lend the thermally controlled regulation system as "acceptible."

Heck, a "hybrid" system does seem interesting however. Just imagine all the bells and whistles - Low visc via fuel and/or coolant dilution, shear wear, or simply too light a grade/over cooling alarms and lights triggered by comparative references of bypass pressure and temperature...also for under cooling, oxidative thickening, or simply too heavy a grade. Hehe.

 

[Gary Allan]

Well, I'd say that the pressure relief surely offers simplicity. 427Z06 probably recalls there was a diesel driver that was either part of a fleet or ran a fleet of (probably) owner operators that were destroying Duramax diesels climbing 8% grades for too long a time with too many items in the "stack" of heat rejection devices. He went into all kinds of thermal calculations and wizbanged all kinds of projected pressure drops/elevations ..friction coefficients of different tube linings ..had custom coolers constructed and whatnot. Yet he knew that he was reaching about 2.5 CST as a peak temp/low visc situation with an 80lb ceiling on max pump pressure. That is, when he (they) were in their death throws where they had to shut down, they had tons of room to tolerate pressure drop/elevation within the cooler circuit without hitting any relief situation that would shunt flow.

Now the guy did a bang up job of designing a system (he was packaging it for sale- so there was a desire to make it "up scale" i.e 30% of $300 vs 30% of $1000

), but I think that, in this situation in particular, he could have just thrown "MORE" at it and slapped a relief valve that would antenuate the pressure drop/elevation across the circuit.

Now this situation had the advantage of the stock system being totally inadaquate for the service environment where the needs way outweighed any liabilities on the other end of any compensation measures could be added to the mix. It also dealt with just one (typically) spec'd visc range that typically operated at a higher standard temp then we're used to.

I tend to like the thermostats ..but it's hard to argue with the simplicity of a relief.

 

[427Z06]

Yep. I'm just not a big fan of adding restriction to redirect flow, in particular, when the oil is cold. Unless that simple check valve has dimensions that are 'larger' relative to the plumbing, it may become a metering valve at the boundaries of operation.

 

[Gary Allan]

I agree. You would surely want your short circuit mechanism to have adequate capacity. In my observations, it appears that a smaller port works as long as the line (or chamber) on either side isn't inherently restrictive to flow (too long while being too narrow) and/or it is close to the source. The effort to accelerate the flow is not that great. That's how I think Permacool and Ford got away with 1/4" relief ports on their sandwiches.


I'm going to play around with my heat exchanger(s) today. If I can find enough fittings I'm going to run a differential gauge across the whole setup measuring at the sandwich ..which has a tapped and plugged relief port. It won't include the filter ..but I don't expect much from it with the visc that I'm currently using (5w-20). I'll also have my little mini-gauges tapped on either side of the differential gauge. I'll know what pressure alterations are generated by the lines and exchanger.

 

[427Z06]

Quote:

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In my observations, it appears that a smaller port works as long as the line (or chamber) on either side isn't inherently restrictive to flow (too long while being too narrow) and/or it is close to the source.

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Recall the flow properties of an orifice.

 

[Gary Allan]

Sure ..and in my fundamental grasp of the event, it normally effects flow nearly twice as much as a linear conduit where normal laminar flow isn't disrupted. This changes in my "comprehension quotient" when not only do you not lose flow due to an intermediary orifice, but the total fluid circuit has downstream restrictions that make the flow through the orifice of equal or higher capacity than the outlet, in this case the engine.

In the illustration below you see (barely) the convergence of the individual flows on the entrance to the orifice .and the turbulence created in the "vacuum" of the exiting flows. Now, without any darn good reason, I'll assume that this flow pattern is going to be retained even if you have subsequent downstream orifices or para-orifices (pseudo orifices

) ..but I think that the pressure impact or the magnitude of pressure alteration would be somewhat neutralized by the down stream restriction.

Speaking way out of proportion: If I had a 6'x20' piece of pipe with a 6" orifice in it ...followed by a 6'x20' piece of pipe ...with a 3" outlet. I would think that the pressure drop/elevation would be marginalized by the ultimate capacity of the orifice to handle the flow without substantial velocity increase when compared to a continuous conduit without subsequent downstream chokes (did I get a bit "drifty" at the end there

)

In any event, there will be a pressure drop/elevation that, in our case, will show the fluid's acceleration through the orifice.

 

[427Z06]

I'm not sure of what you're trying to communicate but I think you're referring to perfectly laminar, inviscid flows where continuity can be applied to the incompressible Bernoulli's equation. I don't believe you want to make those assumptions here.

 

[Gary Allan]

Well, I definitely can't figure out what you just posted

Here's what I essentially meant. That although an orifice normally represents a disproportionate pressure drop/elevation due to either the reduction in flow or the acceleration of flow ..that point is somewhat minimized when the flow is governed by a more substantial restriction. If you have a 1/4" orifice in a 2" line ..but only have a 1/8" tap on that line ..then the orifice is pretty much a non factor in the total added resistance to the circuit.

Top image: virtually no impact
Bottom image: substantial impact
The second orifice represents any and all downstream restrictions.

 

[427Z06]

Yes...much better. Getting back to my point, it may be possible to design and build a bypass orifice out of a chunk of aluminum without the ball check valve.

 

[Gary Allan]

(visions of the Comcast exec that just saw a demonstration of FAST, "It's a pagoda")

Tell me you have more (about this).

 

[427Z06]

Quote:

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(visions of the Comcast exec that just saw a demonstration of FAST, "It's a pagoda")

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Hmmm...you talking about a priority queue data structure implemented with a variant of a binary tree...or the dynamic broadcasting protocols for video-on-demand?

Back on topic. Recall I sent you some flow calculations for orifaces many moons ago? I'll have to run some numbers again but it may be possible to have sufficient flow through a particular oriface that isn't as sensitive to viscosity. This may in affect shunt more to the cooler as the viscosity lowers with temperature.

 

[Gary Allan]

(visions of T2)

"I have extensive files"

Of my 500 message limit, I've kept most of your PMs that included reference data/articles/great stuff ..which is quite a few.

Continuing education is a wonderful thing for the challenged