Oil Pressure Issue

[t-blazer]

From a cold start, my 87 TSi goes to a needle's width above half way on the factory oil pressure meter. After idling for about five minutes, it decreases to about 1/4. From that point, pressure rises with rpm(2.5-3k)to a needle's width below half. Haven't revved past that point. Feedback? Any links here for troubleshooting? Suggestions of any kind greatly appreciated. Thanks.

 

T

[Ironside]

thats about right to me.

[t-blazer]

thats about right to me.

Thanks-I'm just trying to figure out whether I have a low press. issue or what. Appreciate your reply.

[mikec]

The factory/dash oil pressure gauge is not calibrated very well. The display itself is pretty good... it's the sensor unit that varies considerably. Some sensors will start indicating with only a few psi oil pressure; others (most) seem to require about 20 to 25psi before they'll make the needle budge. On most StarQuests, each 1/4 of the display is about 25psi. In theory then half-scale would be 50psi IF the sensor was one of the "good ones" that starts working at only a few psi. For sensors that take 20 to 25psi to kick in, half-scale is more like 70 to 75psi oil pressure... which is normal oil pressure on most healthy StarQuests. Oil pressure goes up/down in sync with RPMs too - that's why many modern engines use oil pressure in the variable valve timing system. Dash oil pressure readings lag real oil pressure by several seconds: when you rev the engine, oil pressure will build up as quickly as the RPMs do even though the gauge will take several seconds to do anything. Proof: start the engine and let it idle... wait a minute until the gauge is holding steady. Now stall the engine, or quickly shut it off and then turn the key back to ON. Notice the oil pressure gauge will still be showing pressure? The pressure inside the engine will be pretty much zero within a second of it being shut off despite the dash gauge saying "there is still significant pressure."

 

Higher idle oil pressure on a cold engine is normal; the oil is thicker and thus easier to pressurize. 15psi at idle is the factor minimum spec; most StarQuests have at least 25psi at idle. 50 to 75psi at "cruise" speed/RPMs is normal.

 

Given the wide variation (car to car) in StarQuest oil pressure gauge readings, the following rules of thumb should be used:

1: learn the "typical" gauge readings (all gauges!) for your car when it's running right. Then, when any gauge starts reading differently, you know something has changed.

 

2: oil pressure: on the 87-later cars, or any StarQuest converted to the auto-lash adjusters (automatic valve lash adjustment "pills") low oil pressure will manifest itself as rapid ticking/clattering from the top of the engine. A little clatter is normal on initial start-up if the engine has been parked for a while... the oil has been squeezed out of the adjusters (also commonly called "lifters" since they do look like dinky versions of old fashioned lifters on pushrod engines); it takes a few seconds for oil pressure to re-pressurize the lifters so they can do their jobs.

 

3: expect different oil pressure gauge readings if you change oil viscosity or if you change brands of oil filter. Some filters have a lot more restriction than others. I noticed a significant increase in oil pressure when I switched to the NAPA Gold filters which are really Wix filters.

 

mike c.

[t-blazer]

Thanks for the extensive background. So by your reasoning, seeing a 1/4 reading at idle would not be out of normal limits, and about halfway at 3k would also be within limits. I found my Chrylser Serv. Man. and it lists 80kPa/11.4 psi @curb idle speed. (kPa = kilos per ??) No ticking/clattering noted, so that seems to the good. I'd consider a different filter in next oil change, good tip. What about the idea of running 20/50 for warm weather? I've seen that mentioned in other posts. Is that relevant or not? Thanks again for your insights,Mike .

 

T-

[mikec]

In SoCal, I've always used 20W-50 conventional oil, or 15W-50 Mobil 1. So far so good. StarQuests were designed for thicker oils than is common on today's "squeeze out ever last bit of fuel economy" engines that call for 0W-20 or 5W-30 oil. That thin stuff (5W-30) is not recommended for StarQuests except in super cold (temps might reach -10 deg F) climates. See the owner's manual.

 

What your gauge is doing sounds perfectly consistent/normal; I wouldn't worry about oil pressure issues on your car. The only real way to know for sure though is to hook up a mechanical oil pressure gauge. You can install one in place of the stock sender unit or in place of the hex-head plug in the front of the engine block, a little below the head gasket and just behind the timing chain case cover.

 

mike c.

[t-blazer]

In SoCal, I've always used 20W-50 conventional oil, or 15W-50 Mobil 1. So far so good. StarQuests were designed for thicker oils than is common on today's "squeeze out ever last bit of fuel economy" engines that call for 0W-20 or 5W-30 oil. That thin stuff (5W-30) is not recommended for StarQuests except in super cold (temps might reach -10 deg F) climates. See the owner's manual.

 

What your gauge is doing sounds perfectly consistent/normal; I wouldn't worry about oil pressure issues on your car. The only real way to know for sure though is to hook up a mechanical oil pressure gauge. You can install one in place of the stock sender unit or in place of the hex-head plug in the front of the engine block, a little below the head gasket and just behind the timing chain case cover.

 

mike c.

OK-I'm in Western NY so the Quest goes in the barn around Halloween. No point in trying to sled around in the winter. So it's summer driving, similar to so cal. 20-50 could be used. I am reassured about the oil press. (non) issue, and continue to browse this site and appreciate all those who have much more expertise than I with respect to the Starquest. I'm out!