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Discussion Starter #1
I read what little there was through the search, but I am needing to know if this sounds alright.

My friend just changed his oil, 95,000 miles mild bolt on car (pullies and exhaust). He went with Cas GTX 20-50 instead of his normal 10-30W.

We just took her out for a spin, and at hot idle the oil pressure shows to be ~36psi. With the 10-30W he says that he usually sees around ~24psi.

Will his motor be alright for a 8-hour trip accross Texas, New Mexico and Colorado? Should he change back to what he was using before (10-30W)? Thanks for any input!
 

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Wow Mike!
I didn't know that a viscosity change could bring the pressure up that much? Is there a callout for max pressure in the manuals?

I ran 20-50 from The Bay Area to Denver and back with no problem, just about 90,000 on the car at the time.
 

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I think the only big difference will be that your gas milage will be alittle worse with the 20-50. I'm not a big fan of thick motor oil so my opinion is biased:)
 

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Discussion Starter #4
It is a big difference, that is why I am posting. I thought for sure that it would go down some, but we were on it hard and sat in 6 lights, but it still remained that high.

I don't have my manual here it is at home, but I dont ever remember seeing anything in there about max pressure. Thanks for the input though, hopefully someone can give me a definate answer on this one.

Definately don't want to run it if there is a chance of something breaking :eek:
 

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Sure, should be no problem especially since one, it's a long trip (it'll thin the oil a bit once it gets warm) and two, it's a higher miliage engine. I run 20W AMSOIL all the time....my engine runs a lot smoother and quieter than when I ran 10W.
 

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Discussion Starter #7
Alright thanks guys!
 

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Your not going to break it. I have a newer long block that I run 5w-30 Mobil1 that always has high oil pressure. When I say high I mean about 45 to 50 psi. That is not pegging the gauge, its about 3/4 to the top. Sounds like you shouls change the oil back to 10w-30 for no other reason than it will make you feel better.
You really have nothing to worry about. 36psi is good for a 5.0.


;)
 

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Mike88GT said:
I read what little there was through the search, but I am needing to know if this sounds alright.

My friend just changed his oil, 95,000 miles mild bolt on car (pullies and exhaust). He went with Cas GTX 20-50 instead of his normal 10-30W.

We just took her out for a spin, and at hot idle the oil pressure shows to be ~36psi. With the 10-30W he says that he usually sees around ~24psi.

Will his motor be alright for a 8-hour trip accross Texas, New Mexico and Colorado? Should he change back to what he was using before (10-30W)? Thanks for any input!
:eek:

I ran 20W-50 and a 160 degree thermostat in my '88 GT a couple years ago. I regret it now being that I spin my engine up high a lot. With that cool of a thermostat I ran before I was driving the car hard sometimes before the engine even got hot. The rings needed that extra heat to seat against the cylinder walls. Using that thick of an oil will starve the upper piston rings of oil being that it is thicker no matter how hot. Before switch to 20W-50 my engine ran smooth. A couple of months later I noticed a bit of smoke from the tailpipes. The smoking got worse and worse after that and before long I had hardly any compression left in the cylinders from the rings being worn. I was constantly putting oil back in the motor every couple of days. Even for a trip like you described there isn't a reason to go that thick with oil. At 95K that motor is still young and doesn't need that thick oil. Switch back.
 

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I put 2qts or 20W50 and 3qts of 10w30 in my Cougar to quiet down my lifters and it runs good w/o any lifter noise like that also.
 

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I run 20W-50 all the time and have had no problems. The higher the pressure the better, even better for long trips. Leave it in.
Len
 

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autoXr1 said:
Sure, should be no problem especially since one, it's a long trip (it'll thin the oil a bit once it gets warm) and two, it's a higher miliage engine. I run 20W AMSOIL all the time....my engine runs a lot smoother and quieter than when I ran 10W.
HUH? Oil thins when it gets warm? That's a new one on me!
 

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dode said:


HUH? Oil thins when it gets warm? That's a new one on me!
Absolutely. Like any fluid, the viscosity is affected by temperature. As the oil warms up, it thins out and becomes more fluid. In fact, the viscosity rating system (10w30) actually relates to the change in viscosity with temperature.

There are standard charts for viscosity (in CSt, CentiStokes vs. temperature) available from ASTM -- ASTM Standard Viscosity-Temperature Charts for Liquid Petroleum Products. I'd love to post an example, but don't see any readily available on the web.

For a little more information, here are a couple of links (didn't have time to more than glance at the second one):

http://www.chevron.com/prodserv/NewOronite/library/li_dictionary_v.htm
http://www.api.org/programs_services/quality/oilguide.pdf

Hope it helps. :)

Chuck
 

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Straight weight oils, yes...multiweight oils...no...

Multiweight, first number is weight out of the bottle (cold), while the second number is the weight at operating temperature. Maybe I misunderstood his post, but that is what I was getting at.

John
 

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Len Schmidt said:
I run 20W-50 all the time and have had no problems. The higher the pressure the better, even better for long trips. Leave it in.
Len
Thats all I use.Castrol actually.;)
 

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dode said:

HUH? Oil thins when it gets warm? That's a new one on me!
You're right, that's what multi weight oils are designed to do....BUT they do definitely thin out.
I can tell you that my 10w-40 is thicker and drains out much slower if the oil/engine is cold as oppossed to when I drain the oil when the engine is hot. it's more like honey when cold and more fluid when hot.
Oils break down with heat
 

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dode said:
Straight weight oils, yes...multiweight oils...no...

Multiweight, first number is weight out of the bottle (cold), while the second number is the weight at operating temperature. Maybe I misunderstood his post, but that is what I was getting at.

John

Even multiweight oils thin at high temperatures, just not as much. Don't know if you were debating that or not, but thought I should clear that up.

Billy
 

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Multiweight oil thins, but not as much. Note that "not as much" is still quite a bit, because the viscosity of regular oil changes very significantly with temperature. Here's how it works:

There is a pretty standard relationship for how a normal (non-multiweight) oil will change viscosity as it warms up. The viscosity of regular grade oils is rated in cSt at 40 degrees celsius. In other words, a regular 10w oil has a viscosity of 10 cSt at 40 degrees. For normal oils, you can predict pretty accurately what that viscosity will change to at 100 C.

Now, take the example of a multiweight oil like 10w40. This oil has a viscosity of 10 cSt at 40C, but has a viscosity at 100C similar to what would be expected of a 40w oil. This is still thinner than the 10 cSt viscosity at low temperature, but not as thin as the straight 10w would be.

Note also that this means a 5w30 and 10w30 multigrade both have about the *same* viscosity at 100C or 212F. However, the 10w30 is thicker at startup until it warms up to temperature.

Chuck
 
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