oil pressure drop after going to full synthetic

[BigDuke6 17]

My engine is new so my builder had me run a 15-50 mineral race oil for the break in. During this time, I recall my oil pressure on the autobahn being at least at 50 PSI. AFter going to to Mobil1 5W-30 full synthetic, my oil pressure dropped. It was at 50 psi at start up and while warming up. But under WOT on the autobahn, it is more like 37 PSI. I recall a rule of thumb of 10 PSI per 1000 rpm. Does synthetic oil drop the pressure a bit? By the way, I know that I am a half L down. I have a 7 quart oil pan (6.6 L) but the oil change place only put in 6 L. I don't think that should make a huge difference. They owe me the .6 of a L and I plan to do it when they open back up after summer vacation.

[sportsroof69 13]

It's not cause by going from conventional to synthetic. Your oil pressure is lower because you went from a 50wt oil, to a 30wt oil. Thinner oil = less pressure.

[LindenBruce 27]

Synthetic should not have caused the drop in pressure. I think it's because of the thin oil they used. I prefer a 10w30 minimum in these older engines, even if they have been rebuilt. And if you have bearing clearances centered around racing or high performance, then you will need a heavier oil anyway. Bruce

[BigDuke6 17]

Is my OP ok?

[stangnet33 88]

yes dropping from a 50 to a 30 will equal less oil pressure. I also wouldn't be to quick about jumping into a synthetic oil.

[sportsroof69 13]

Is my OP ok?

 

If its 37 at WOT, that's low for my liking. What is it at full running temp, and at a steady highways speed?

[BigDuke6 17]

If its 37 at WOT, that's low for my liking. What is it at full running temp, and at a steady highways speed?

 

37-40 psi cruising at 100 mph. Engine temp is 180

[sportsroof69 13]

I hope you have overdrive! Lol

 

I could live with 40 at a steady speed. How many RPMs is that, and does the pressure go up when you add throttle? Are you reading this on a mechanical gauge? What kind of oil pump is in it?

[BigDuke6 17]

I hope you have overdrive! Lol

 

I could live with 40 at a steady speed. How many RPMs is that, and does the pressure go up when you add throttle? Are you reading this on a mechanical gauge? What kind of oil pump is in it?

 

No OD. That RPM is about 5500. I max out at 6500. The OP seemed like it stayed the same under WOT or at 100 mph or at 80 mph.

 

I have a moroso 7 qt oil pan, windage tray, and a std vol oil pump. Like I said, the oil shop put in 6 L when they should have put in 6.6 L of oil. I should also verify they used the correct oil filter.

[sportsroof69 13]

Yes, and you also said cruising at 100. So it's the same cruising at 100, and at WOT?? I realize you're on the autobahn, but do you cruise at WOT?

 

What is the pressure at steady throttle cruising at say 60 MPH? Is it the same as if you're standing on it?

 

Being a little low on oil isn't going to affect the pressure. Are you reading this on a mechanical gauge, factory gauge? Or what?

 

 

Regardless, if it's making 40 while you're at 5500 RPMs and WOT, that's not enough IMO.

 

Do you know which pump is in it? Some pumps, like a M88 Melling, have a plug in the bottom that you can take out, and trim the spring. This will raise the pressure of the pump.

 

Or you can run thicker oil

[BigDuke6 17]

Yes, and you also said cruising at 100. So it's the same cruising at 100, and at WOT?? I realize you're on the autobahn, but do you cruise at WOT?

 

What is the pressure at steady throttle cruising at say 60 MPH? Is it the same as if you're standing on it?

 

Being a little low on oil isn't going to affect the pressure. Are you reading this on a mechanical gauge, factory gauge? Or what?

 

 

Regardless, if it's making 40 while you're at 5500 RPMs and WOT, that's not enough IMO.

 

Do you know which pump is in it? Some pumps, like a M88 Melling, have a plug in the bottom that you can take out, and trim the spring. This will raise the pressure of the pump.

 

Or you can run thicker oil

 

WOT is 6400 rpm. I can cruise 100 mph at 53-5500 rpm. I have a melling M83 std vol pump. My oil pressure gauge is an autometer and it and the sending unit are basically new This just happened with the oil change. I will put a mechanical gauge on there to verify what the gauge is saying. Is pressure the same as flow? Could the pressure be reading lower because the viscosity of the synthetic is so thin compared to Dino juice?

[sportsroof69 13]

No. Pressure and flow are different. It has nothing to do with conventional vs synthetic. It's a function of weight, and you went to a thinner oil, so the pressure went down.

 

WOT and max RPMs are 2 different things, but it still doesn't sound like its making enough pressure. You could simply put a thicker oil in it, or you can trim the spring in that pump to make more pressure.

 

Do you have any idea what the bearing clearances were when the engine was built? Just for reference, with a 10W-30 oil, mine makes 55 psi going down the highway at 2800 RPMs, and will go up to 68-70 and soon as I add throttle. Idle doesn't really matter as long as it's making pressure, but mine idles at about 35 psi. That's at full operating temp. It makes 60 at idle on a cold startup. We DID trim the spring in my oil pump.

[Klutch 17]

Synthetic should not have caused the drop in pressure. I think it's because of the thin oil they used. I prefer a 10w30 minimum in these older engines, even if they have been rebuilt. And if you have bearing clearances centered around racing or high performance, then you will need a heavier oil anyway. Bruce

 

FYI, the "10" in 10w30 is irrelevant when the engine is at operating temperature. The 10 means the oil provides the protection of a 10 weight oil at startup. The 30 means the oil provides the protecion of a 30 weight oil at operating temperature.

 

Thus, the difference between a 5W-30 and a 10W-30 is the 5W-30 provides better protection in very cold weather. Once at operating temperature, both oils are the same.

 

For the OP, you might want to try a 10W-40 oil. Typically, I would recommend 5W-30 or 10W-30 for a new engine. But typically, people aren't cruising at 100MPH. The 10W-40 should give you a little more oil pressure at operating temperature while still not being too heavy to get where it needs to be. You're probably fine with the synthetic 5W-30, but I can see how a little more oil pressure would provide that warm and fuzzy feeling. :smile:

[LindenBruce 27]

Unless you're drag racing, I would use a High Volume oil pump. Just my personal preference. Your engine was prolly build with racing spec bearing clearances, which are larger than factory clearances. Go to an HV oil pump and use 10/40 oil. Bruce

[BigDuke6 17]

FYI, the "10" in 10w30 is irrelevant when the engine is at operating temperature. The 10 means the oil provides the protection of a 10 weight oil at startup. The 30 means the oil provides the protecion of a 30 weight oil at operating temperature.

 

Thus, the difference between a 5W-30 and a 10W-30 is the 5W-30 provides better protection in very cold weather. Once at operating temperature, both oils are the same.

 

For the OP, you might want to try a 10W-40 oil. Typically, I would recommend 5W-30 or 10W-30 for a new engine. But typically, people aren't cruising at 100MPH. The 10W-40 should give you a little more oil pressure at operating temperature while still not being too heavy to get where it needs to be. You're probably fine with the synthetic 5W-30, but I can see how a little more oil pressure would provide that warm and fuzzy feeling. :smile:

 

considering that I only drive the car late April through September, I don't think I need such a thin oil. The builder suggested a 15W-50 oil and I think I will add the missing .6 L in the form of 15W-50 to what I have now and use that at the next oil change.

[sportsroof69 13]

It's not a good idea to mix oil weights, especially if one is Dino, and one is synthetic.

[BigDuke6 17]

It's not a good idea to mix oil weights, especially if one is Dino, and one is synthetic.

 

I have mobil 1 5W-30 synthetic in there. I was going to mix in mobil 1 15W-50 synthetic. I read that a lot of racers do this.

[LSG 15]

Duke, if you're adding Mobil synth to Mobil synth, you should be okay. But what is the thinking behind the 10-30 ? thats like, weak coffee, not oil. If your engine has not already sustained damage from too low of pressure, and yes, yours is too low, get rid of the 10-30, replace your oilpump with an HV and run 15-50 instead. LSG

[BigDuke6 17]

the problem seems to be solved. I had not driven my car since the low oil pressure episode at the end of August. I changed the oil out today, taking the 5W-30 from the mustang and putting it into my DD and putting Castrol 10W-60 in the mustang. The oil pressure at idle is 37 psi and 50 psi at 50 mph, so it seems like it is ok.

Edited October 8, 2012 by BigDuke6

[69_Mustang 26]

10w60 is what we HAD to use in the E46 M3. It's a very good oil.

 

Looking like anywhere from 5w40 to 10w60 is ok to use in these engines? Any ideal weight? I have a stock internal 351w.

[sportsroof69 13]

What weight you use just depends on how the engine was built. More tolerant bearing clearances will need a heavier oil.