posted on November 24, 2010 11:02
I am wondering about gauges and their importance; specifically, oil temperature versus oil pressure. If you had to choose between the two, which one would you pick? And does it matter for a street car versus track car?
Po-TAY-toe, Po-TAH-toe… For the most part, it's a matter of personal preference. As long as you're monitoring something related to your engine's vital signs, you're more likely to notice when anything goes wrong. If it is me deciding between an oil pressure gauge or an oil temperature gauge, I'd go with an oil pressure gauge. The loss of oil pressure often results in complete obliteration of the engine. The engine's main and rod bearings are made of soft metal such as tin, copper, and zinc (some older engines used lead) with alloying agents like iridium added to increase the mechanical property of the metal's grain. Softer materials have greater embedability, which means they can more easily absorb hard contaminates such as dirt, metallic debris, and casting sand. Since the softer bearing surfaces soak up the contaminants, it is less likely to damage the hard steel surface of the crank's journals if the incompressible, pressurized oil film fails to eliminate contact between the bearings and journals. A tiny bit of oil is lost at each rotation due to the centrifugal pumping action created by the rotating rod journals. If the oil pump can't replenish the oil quickly enough and oil pressure drops off considerably, the crank will quickly eat up the soft bearings and the material flakes away, disrupting the oil film. The bearing shell will then fuse itself to the crank, scoring the crank journals. The rods, pistons, and valvetrain follow quickly afterwards if the engine continues to be driven. At high load/rpm, the complete loss of oil pressure can destroy an engine in milliseconds. Obviously in that case, either gauge would be useless!
Oil temp is a good indicator of the readiness of your engine, such as if it's overheated or too cold. But low oil pressure can indicate if your oil pump is getting a little long in the tooth, if the oil pickup screen is clogged, if there is debris in the oil or if the oil is dirty and it's time for an oil change and new oil filter. It can also be a sign of excessive wear (such as high mileage engines) or low oil volume. While there is no exact one-to-one relationship between oil pressure and oil temperature, since oil becomes less viscous at it warms, oil pressures start out higher in cold starts and then start to drop as oil temps get warmer so there is some indication of oil temps when monitoring an oil pressure gauge. In either case, if the oil temps are sky rocketing or if oil pressure has dropped off considerably, it's time to let off and investigate.
|Engine bearings must be soft enough to soak up metallic particles but still have a high load bearing capacity since the engine's reciprocating parts transfer thousands of pounds of force to the bearings even though an incompressible oil film prevents metal to metal contact.
|These bearings are ACL tri metal heavy duty Formula Atlantic bearings from Technosquare's Toyota 4AG engine. They are Tri Metal construction, which provides superior load bearing capacity, but they don't have the typical zinc layer that gives a bit of embedabilty. The thought is this zinc layer reduces heat transfer and isn't necessary in a racing engine that is cleaned carefully during assembly.
There are other reasons why I think an oil pressure gauge would be more beneficial than an oil temp gauge, especially on the track. When cornering hard such as when road racing or accelerating hard such as at a drag strip, many engines will see a drop in oil pressure which could indicate an oil starvation issue. For this reason, oil pressures should be closely monitored, especially on the track. Oil pressure should also be watched with turbocharged cars, though ball bearing turbos require less oil than journal bearing turbos and may even need an oil inlet restrictor depending on your engine's oil pressure. If the turbo is starved for oil, you may be shopping for a new one shortly. Finally, with engines such as the Subaru EJ25 which is known for broken oil pickups, or the Nissan/Infiniti SR20DE, which have shallow oil pans that easily get dented near the pickup, an oil pressure gauge is extremely important. Of course, the VQ37VHR and BMW 330 (and other engines that use a lot of oil to activate their variable valve cam timing systems) are well known for their high oil temperatures, so it might be a good idea to equip your car with an accurate oil temp gauge if your engine has this known problem.
Wednesday, November 24, 2010 10:13 PM
Good article Sarah. Keeping tabs on temps is a must for all cars. I used to tow a lot, and im a friggin nut for cooling systems. Never use a tube/fin style oil cooler if there are plate/fin cooler for the same application. One of the projects im collecting parts for, is a whole setup on my truck to monitor trans and engine oil temps, and engine oil pressure (3 gauges). Gotta be careful not to make it look ricey (american truck).
I love reading stuff related to my projects!
Thursday, November 25, 2010 5:47 AM
Does the engine oil go through some process to change its properties to be better suited for engine use? I ask because naturally occuring oil from the earth is compressible. Is it that the pressures just are not great enough to compress the oil in an engine?
Thursday, November 25, 2010 6:56 AM
Lol, those of us without the double-DIN bling just put them in the dash ;)
Good advice! The coolers I almost rant on, but see so few of them, the volume of oil in the SR20 when it's full is still shockingly low @3.9 qts or so, the cooler and piping adding another quart or so alone makes it worth the hassle. I see people who've cooked motors still put the next one in w/o gauges or coolers...flat learning curve.
Thursday, November 25, 2010 7:24 AM
Oil for all practical purposes is not compressable.
Thursday, November 25, 2010 5:30 PM
If sr20's are equipped with such a poor oil volume, why are there not more amateur racers running dry sumps? Yes, I know that they are expensive, but other than a moroso kit for hondas, I haven't really seen or heard much about dry sumps for other engines like the 4g63 and the SR20.....
Thursday, November 25, 2010 6:40 PM
All cars should be equipped with a minimum of 6 gauges from the factory: Tach, Speedo, Gas Level, Coolant Temperature, Oil Pressure, and Battery Voltage. Heck, my daily-driver truck has all those, plus oil temperature, transmission temperature, and manifold vacuum (the latter three added by me).
Of course, the average dimwit driver wouldn't know what half of those gauges mean, anyway...
Thursday, November 25, 2010 7:46 PM
mmm. really? no one mentioned a Wideband A/F gauge/display? PLX M300 is actually the only gauge i have.
Friday, November 26, 2010 9:52 AM
Wideband O2 is really only needed if you are doing tuning on a car with forced induction or increased compression. If you've got a track car with a relatively sock engine (like a lot of Miatas out there, for instance), you don't need an A/F gauge.
Friday, November 26, 2010 3:11 PM
@ Dusty - I am not so sure about that. Most factory calibrations are so far off, the gauges might as well be lights. They might be pretty to look at, but don't really tell you much. Some lesser knowledgeable drivers get fixated on the gauges, when they really aren't telling them anything. I think most drivers out there, need to pay attention to the road, and if you need a gauge, put in a good aftermarket calibrated gauge. With newer OBD II cars, you can monitor a lot of things from a single data stream.
If I had to pick oil temp or pressure, its pressure every time. The temperature doesn't matter much if the pressure is 0. Oil temp generally follows/leads water temp in most engines.
If you run a cooler, make sure you DUCT it. Try and make the air flow though the core, both in, and out of the core. Air takes the path of least resistance, and if it can go around your oil cooler, and not though it, it will.
Friday, November 26, 2010 11:23 PM
Good writeup Sarah!!
Back in 2003 when I dropped by SR in my S13, all my friends were ribbing me about spending as much as I did on my Defi Link gauges and they thought the gauges were bling for the sake of bling. Yeah, the first week of driving the car proved them wrong as I hooked up a large flashing shift light to the column that could be triggered by the output of the gauge controller. Sure enough, in the first week the light went off every day to tell me of overheating issues. Those gauges paid for themselves within about 2 weeks. Meanwhile the factory temp gauge was useless with readings of "Off", "Normal", and "Buy a New Engine" settings. I also used the oil pressure to let me know that I was needing an oil change... Good writeup Sarah.
Saturday, November 27, 2010 5:29 PM
Great article, I really appreciate your warning about stock guages! Most of the gauges in cars these days are pretty worthless, so if you're serious about the data, you'll need an aftermarket solution.
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