low oil pressure (1 Viewer)

[dtech]

My 99 lx470's oil pressure gauge drops below the bottom mark when in gear at idle. stealer says the check engine light should come on if the oil pressure is actually below normal operating parameters. anyone else experience this? any diagnostic procedure for testing the oil pressure sending unit? or the gauge in the cluster?

 

[gray]

What does the gauge do when you are cruising down the road; ie at 30, 50, 70mph, or accelerating hard? How about at first start-up in the morning? Does it go up to the top line or above, ever?

What viscosity oil are you using? Did you recently change the oil type, brand, viscosity, different brand of oil filter, what brand of oil filter, how often do you change oil, always the same type, how many miles on the engine, any major work done on the engine, ever use an engine flush/cleaner, etc,etc,etc.

The quick answer(opinion) is that if you use synthetic oil like a 0W-30, your pressure will go down more at idle. Years ago I rode in a new (test) corvette at the corvette test track which was using Mobil 1 5W-30. I recall noticing the oil pressure was only 5psi at idle, which I thought was very low; then the driver stepped on it. When I got my eyeballs out of the back of my head and looked at the reading again, the pressure had shot through the roof. The oil pump makes more pressure at higher rpms.

Post more details on the oil type, etc and what you have observed before.

g

 

[dtech]

5w30 non-syn, toyota filter, start up the oil pressure is high(i cant tell you what psi because it is not a graduated gauge) about 3/4 of the way, after warm up the oil pressure seems to change with the engine RPM as it should. ie up to about half way when under load/acc. in the owners manual it says the gauge should read between the first mark and the third. being that mine will dip below the first when hot at idle in gear (stop sign) i assume that ether the sending unit is not creating accurate resistance at low pressure condition or the gauge is not accurate in displaying. no engine work that i know of. i got the lx two months ago.

 

[EdsCruisin]

I believe I saw a test procedure for the guage in the FSM. It is a matter of pulling the dash apart and doing electrical tests via the plug pins.

 

[gray]

If the vehicle has a lot of miles, you could perform a do-it-yourself engine flush; or internal cleaning. More important if conventional oil has been used it's entire life cause it will have more crud in it than if the previous owner had always used synthetic.

Sometimes IME a very dirty engine (internally sludged up) will have lower pressure than a desludged engine.

 

[NMuzj100]

Low RPM on a thinned (hot) oil will not show much pressure on the 100's gauge. Many, Many posts on this.

By "below the bottom mark" do you mean totally below the scale ?

Maybe we need a FAQ thread.

 

[NeilC]

Its the damn energy conserving oil. The higher the pressure, the more energy is required from the engine to pump the oil. I have had several different vehicles and all of them had "low" oil pressure at hot idle. I think it happened about 10 years ago. So many cars do not have oil pressures an more so most being don't know what their pressure is. I think it is harmless because there is no load on the engine at idle. Also the engines idle lower than the did. A good rule of thumb is that yo need 10 psi per 1000 rpm. My engine idles at 600-700 and oil pressure when hot at the 1/4 mark. Other vehicles were the same. As long as it go up alot while driving with a load on it, its fine.

 

[SWUtah]

My 99 lx470's oil pressure gauge drops below the bottom mark when in gear at idle. stealer says the check engine light should come on if the oil pressure is actually below normal operating parameters. anyone else experience this? any diagnostic procedure for testing the oil pressure sending unit? or the gauge in the cluster?

Dealers right if the pressure is low the light will come on. gauge is not accurate, ignore the guage. Your fine. There have been several threads on this and the light is the key.

 

[richg]

Personally, I'd do some digging to verify whether or not there is a problem. Be it testing the sending unit, or swapping in a real pressure gauge for a quick test. I'm not one to rely on an idiot light if I think there may be a problem, especially considering how low those warning light switches can end up being set.

Also, sludge in a motor after the oil pump raises oil pressure, sludge before it would lower it, however, normally there isn't a whole lot of area for sludge to accumulate before the pump.

And low oil pressure under any conditions is not fine -- even at idle.

rich

 

[NeilC]

Also, sludge in a motor after the oil pump raises oil pressure, sludge before it would lower it, however, normally there isn't a whole lot of area for sludge to accumulate before the pump.

And low oil pressure under any conditions is not fine -- even at idle.

rich

Almost all sludge related oil pressure problems are caused by the pickup screen being clogged. Some problems relate to the oil drain down passages in the head getting clogged not allowing the oil to drain back to the sump. I have never seen sludge cause a high pressure situation. High pressure is usually caused by a stuck bypass value or pressure relief valve. Low pressure i.e. 8-10 psi at idle when hot is very common with newer engines. Combine the relatively light weights with higher operating temps and you end up with low pressure at idle speed. You can't escape the laws of physics. Newer engines run hotter now because of emissions requirements combined with the fact the engineers are now getting more power from smaller displacement engines.

 

[rusty_tlc]

A really stupid question, did you check the oil level?


RE: Gages,
In the world of electronic testing we label non-calibrated equipment "For Indication Only". IMHO this is how all OEM automotive gages should be labeled. They are not instruments, they are indicators.

 

[cary]

If the vehicle has a lot of miles, you could perform a do-it-yourself engine flush; or internal cleaning. More important if conventional oil has been used it's entire life cause it will have more crud in it than if the previous owner had always used synthetic.

Sometimes IME a very dirty engine (internally sludged up) will have lower pressure than a desludged engine.

The 100 is very easy on oil, the chance if it being sludged up are virtually none, unless changes been at greater than 10k mile intervals on mineral oil.


Most likely the pressure sender is bad or the gauge is out of whack. Throw a mechanical gauge on it and see what the actual pressure is at hot idle. Anything more than 7psi should be fine.

Did you notice this change right after the last oil change or did it come on gradually. If it isn't the gauge there could be other potential causes including, 1) change in brands of oil to one that is formulated on the thin side of the 30 weight spectrum, or 2) plugged injector leading to fuel dilution and shearing. A simple used oil analysis will tell you if you have a fuel dilution issue.

 

[richg]

Almost all sludge related oil pressure problems are caused by the pickup screen being clogged. Some problems relate to the oil drain down passages in the head getting clogged not allowing the oil to drain back to the sump. I have never seen sludge cause a high pressure situation. High pressure is usually caused by a stuck bypass value or pressure relief valve. Low pressure i.e. 8-10 psi at idle when hot is very common with newer engines. Combine the relatively light weights with higher operating temps and you end up with low pressure at idle speed. You can't escape the laws of physics. Newer engines run hotter now because of emissions requirements combined with the fact the engineers are now getting more power from smaller displacement engines.

I guess I've never had a motor that developed any sort of clog on the oil pickup screen. Yes I've seen pictures of this online and would have to say its a combination of engine design, oil used, and frequency of oil changes. On all the teardowns I have done on motors, the only sludge I've ever found is the accumulation of "gunk/goo" on internal oil passages. Obviously the synthetic oil motors were MUCH cleaner on the inside than the regular oil motors.

I agree 100% that as a general statement, operating oil pressures are lower than they used to be. However, assuming his gauge is "accurate", his current operating idle oil pressure is LOW. Thats why I think more investigation is warranted. The likely case is the sending unit is simply bad, but if its my truck, I'm not going to roll the dice on a bad sending unit and risk blowing an engine.

rich

 

[NeilC]

I guess the question should be, what is he calling the "bottom mark" ? If he is referring to the mark one up from the bottom of the scale and the pressure drops just slightly below it when idling hot, I would say all is well. If he is referring to the very bottom of the scale, I would dig in and do some investigative diagnostic work like checking the pressure with a mechanical guage to see if it is a sender problem/guage problem or if the pressure is really that low. I have seen different oil filters cause different pressures. I currently run M1 high mileage 10w30 which is a fairly heavy 30w and my hot idle pressure is at the first mark up from the bottom of the scale. In Louisiana I do not need an oil that will flow at very cold temps. Synthetic oil generally flows easier than the same weight conventional and thus runs a lower pressure. The film strength on a good synthetic is very high which means it doesn't need a lot of pressure to protect against friction. All of this requires that there be oil in the engine but I assumed anyone would check that first before posting on a forum like this to solicit advice from idiots like me.

Does anyone know where the port is on the engine to install a manual guage?

 

[NMuzj100]

A really stupid question, did you check the oil level?

Not stupid at all. The basics are the basics for a reason.

Does anyone know where the port is on the engine to install a manual guage?

Remove the oil pressure switch from the straining unit (filter mount) and attach the gauge in it's place.

Per the FSM....

anything above 4.3 PSI at idle is kosher. That would read low on the indicator/gauge.

at 3000 RPM then pressure should read 43-85 PSI.

Gauge/indicator is covering a "normal" range of over 80 PSI. I think your gauge is working as it should and the truck is working at it should.

 

[cary]

Synthetic oil generally flows easier than the same weight conventional and thus runs a lower pressure. The film strength on a good synthetic is very high which means it doesn't need a lot of pressure to protect against friction.

Not true on both counts. An oil that is thinner is rated as such. Film strength of oils is mostly a function of weight, not basestock composition.

 

[dtech]

yes i checked the oil level....by bottom mark i mean the last mark on the bottom....or i guess you could say the first mark..... its fully under it... i know its a reference gauge( not graduated) thats why i was looking for a test procedure for the sending unit and alike.....just because the CE light didn't come on doesn't mean the gauge is reading improperly....maybe the sending unit that the ecu reads is faulty...i have to assume there is two sending units if one reads low and the other doesn't show a problem.....i think it would be silly to assume the oil pressure is fine when one warning device is showing a problem.....

 

[dtech]

thanks NMuzj100 thats the type of info i was looking for.

 

[NeilC]

Not true on both counts. An oil that is thinner is rated as such. Film strength of oils is mostly a function of weight, not basestock composition.

The "weight" is only rated at 2 specific temps, -25 and 100 C. Different oils act differently at other temps. The problem is convetional oils use a base oil of the first number and add polymers to thicken it up at the higher number. Synthetic oils are far better at "acting" thick at higher temps and thin at lower temps. Most good synthetics do not use polymers. The film strength of a 10w30 synthetic is way higher than a 10w30 conventional oil. Remember the 10w30 conventional is a 10 weight oil with non oil additives while the 10w30 synthetic is a true 30 weight at 100C. The pour point of a synthetic will also be lower than the same weight conventional oil.

 

[dtech]

all oils have additive packages, even single weight oils.....or did i misunderstand what you were saying?