Oil pressure too high means oil is too thick ?

MrPerfect2

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Been reading about oil weights and came across a few statements that higher oil pressure is not too good . Keep in mind I have a stock 91 5.0 and basing my readings on stock gauge ( which seems pretty responsive on throttling ) needle up about 3/4 on WOT , and 1/4 at idle . I am going to put 5w-30 full synthetic in now ( I live in wash DC - so gets to 10 degrees in winter ) just wondering what you mechanics think - I was going to go with 10w-40 in spring for the 100 degree days . Thanks
 
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revhead347

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10W-30 all year round in DC is fine. The stock gauge isn't really a gauge; It's just an on/off switch that triggers at 8psi. If the gauge is moving around too much, it's your alternator, not your oil pressure.

Kurt
 

MrPerfect2

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I just learned that synthetic oils are very good at cleaning out grime ( the type of grime that may be coating my seals and holding back leaks , lol) car has 110k miles on it and don’t want to introduce problems -
 

General karthief

wonder how much it would cost to ship you a pair
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I agree with the 10w-30 recommendations.
news to me about the gauge being activated like a switch. The 'dump truck' has a gauge that is activated like a switch and does not sweep higher when started but rather snaps to the same spot. It does not move around at all even when the alternator moves around, on the other hand the stock gauge in my mustang (when I had it hooked up) would sweep upon start and move around with engine rpms and also would read lower after the engine reached operating temp.
i'm not saying you are wrong, just that was how mine acted.
 

MrPerfect2

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I will go with a conventional higher mileage oil ( has seal saver additives ) seems like a reasonable choice - but for cold winters , why not 5w-30 ( curious ) ?
 

General karthief

wonder how much it would cost to ship you a pair
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Ok,
compare the additives between that and the regular synthetic blend, unless it's the same price then go for it, likely can't hurt anything
 

revhead347

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news to me about the gauge being activated like a switch.
I'm surprised by that. Ford did away with an actual gauge in the 80s. Customers were freaked out by the oil pressure gauge moving around on them when engine RPMs changed. After that they just put a sweep style gauge that went to a specific point on the scale when the sender hits 8psi. The ground is regulated off the sender, but the positive is obviously affected by voltage.

I am old enough to remember when Synthetic oil was expensive. When I was in high school it was about 6 times more than conventional oil. Now that Walmart sells a 5qt jug of Mobil One for $23.88, why would you use anything else? There are lots of rumors about Synthetic oil, most of them are un true. No it doesn't leak out faster. You do have to change it just as often, because dirty oil is dirty oil. However, if you are the kind of person that drives 3000 miles every 5 years, it does not break down like conventional oil. So if it isn't dirty, you don't have to change it.

Kurt
 
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General karthief

wonder how much it would cost to ship you a pair
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Learn something every day.
now that school is out, can I have a drink?
a Jack and Coke sounds pretty good right now and I usually don't drink much
 

revhead347

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They do make a synthetic blend higher mile with a seal saver
In my experience, anything that keeps a seal from leaking hurts the component the seal is protecting from lack of lubrication. This is particularly true for AC components. The only fix for a leaking seal is a new seal. I am not sure if the high mileage stuff has any merit. Do the proper maintenance, and it will go as long as God intended.

Kurt
 
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revhead347

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Learn something every day.
now that school is out, can I have a drink?
a Jack and Coke sounds pretty good right now and I usually don't drink much
Lol. I am already a few deep to be honest. I flew with a Captain this week that spent 4 days bitching about his distrust in the Union because they were not opening negotiations with a 100% pay raise, like, because the company could mathematically afford it. A total disconnection from reality. After 4 days of that, I went straight for the whiskey tonight.

Kurt
 
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FastDriver

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Beg to differ there, Kurt, though you're right about your SN95. Fox senders were better than switches, but still suck and not to be trusted:

Fox:
FoxBodyOilPressureCircuit.jpg


SN95:
OilPressureGauge96a.jpg


Anyways, OP, your oil pressure is most definitely NOT too high. Probably a bad sender. They're cheap. Easy to replace.

Old rule of thumb was 10 psi for ever 1k rpm. Pressure, not just oil-presence, is what keeps the metal components separate. So, high pressure, in my opinion, is not a bad thing. Perhaps I have something to learn there, though, as I have never heard of any problems from too much pressure.
 
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FastDriver

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10w-30 is what is recommended for these engines, no need for the 5w.
on the subject of synthetic oils, they do not cause leaks, they will not 'clean' sludge from the engine. Old mechanics tale.
You challenged me on this line of thinking earlier this year, so I swapped 0W-40 Mobil 1 Synthetic into the 166k mile convertible. It went 2k miles and 4 months and was beat on a little. It did not develop any noticeable leak. So, I'm on your side until I see evidence otherwise.

I run synthetic in everything else I own... The higher-powered ones do leak, though. They never ran anything but synthetic, though. So that's not the issue.

On the "W" subject, that number primarily tells you how much the oil thickens at colder temps and thins at higher temps. All oils thicken at low temps. At operating temp, no matter what the "W" or even if it's just straight 30, they all act like a 30 weight. 10W will be thicker at cold start than 5W, and 0W. Just for clarity, though, All of the above will do just fine, but the lower the W the better the oil will be on cold start... the more quickly they'll be protecting your motor.

All that said, W numbers are not directly comparable from one weight to the next. The 0W-40 I run is still a thicker oil than a 5W-30 all the way down until around -35*C, based on Mobil 1 data.

All that said, OP, if you want to run 5W, or 0W, no worries.
 
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MrPerfect2

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Thanks fastdriver - the switch diagram was awesome explanation ! As was the W info . The reason I considered synthetic is many cold starts in winter - that stuff seems to flow great when very cold - I will look for a syn/syn blend for higher mileage vehicles ( has seal saver additive ) - one question , back to original title - all things equal , will a 40 weight yield higher oil psi than a 30 weight ? And which is better for 100 degree days - also based on stock Fox gauge , where do I want the needle at idle and where at harder throttle - thanks
 

General karthief

wonder how much it would cost to ship you a pair
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#1 don't depend on the stock gauge, get a aftermarket gauge even if it's just temp to see where your stock gauge is reading.
the stock gauges will read different between different car and even changing the sending unit can change the gauge readings
 
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FastDriver

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Think about it as a system. When it's pressurized oil is maintaining a boundary layer, while intentionally allowed to leak through the gaps. It's also meant to be splashed onto the cylinder walls and piston bottoms. It also has to be pushed up through the valve train.

Pressure is resistance to flow, and it's upper limit will be dependent on the difference between the oil pump's capability and the volume leaking through the gaps in the system.

Those gaps widen on higher mileage vehicles. So it can make sense to go to a thicker oil eventually. But if those gaps are too tight, there may be too much resistance in the oil passages to allow the passage of a thicker oil and it may end up starving the oil passages further downstream. What you'll get is high pressures at the pump and low pressures in other important places.

I've never really tried to figure where in the order the oil pressure sender is placed, but where you read the pressure will affect the answer to your question.

Nevertheless, I do not believe running a thin 40 weight will hurt anything on a stock 5.0 in the summer. Listen to your valvetrain clatter and if it's considerably worse on cold start, you should probably go back to 30 weight.

Like Karthief said, stock gauges suck. They're not meant to be compared across the board. You should have pressure and it should act like it normally does. If something changes from what you normally see, then investigate. Otherwise, leave it be.
 

MrPerfect2

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I did oil change today ( first on this fox - just got it 6 months ago , had one in 93 though ) decided on quakerstate semi synth , high mileage - had good amount of zinc and moly plus a seal conditioner - so I am adding the big 5 jug in and watching funnel - looks fine then I realize the baffle in valve cover is hindering the flow - so .... as I pour in funnel it leaks out the side and on to ground ( over header of course ... ) lost approx a quart on ground ... since I only had the 5 quart Quaker , I had to use a backup brand in garage - Walmart Supertech full synth . Oh , went with the motorcraft filter ( after seeing the Fram cutaway video ) Both are 5-30 oils . Well , the beers were flowing and storm approaching - long story short - oil on dipstick is an inch higher than the full mark . What happens if 6 quarts in 5 quart system - drove around block and seems fine , Should I drive for a while and drain a quart if still high ? Lol - is this an amateur move