5W20 in my 1988 Mustang GT

[brianl703]

I had a coupon for a free oil change and tire rotation from the Ford dealer and my 1988 Mustang GT needed both of those so I took it in.

They put 5W20 in it. It has the 5.0 V8.

It's been about 1000 miles.. I've noticed nothing different vs. the 5W30 that was in it before.

The last Ford TSB I saw regarding 5W20 only recommended 5W20 for Mustang 5.0s as old as 1993, nothing older.

I wasn't planning to do this experiment but since the oil's in there now, why not?

 

[chevrofreak]

If you feel the need to run something thicker, either use 5W-40 synthetic (Shell Rotella T) as top-off, or suck out a quart and replace it.

 

[Bryanccfshr]

I personally think you will be fine for most uses. 5w20 has proved to be simpky 5w30 light. the differnces between the grades is not all that significant with 5w20 giving better overall economy due to lower viscosity throughout the operating range.

 

[OVERKILL]

You'll be fine, I ran 0w20 in mine for an entire winter with no ill effect.

The TSB only goes back to '93, likely because '93 was the first year of hypereutectic pistons for the HO. The earlier pistons were (looser clearance) forged aluminum.

 

[rg200amp]

5w20 will do great.

 

[Nickdfresh]

I wouldn't worry as your 5W-30 just sheared down to 5W-20 anyways. And if they used Motorcraft, then it's a synthetic blend. Most 5W-20s are probably syn blends whether they say it or not.

 

[Merkava_4]

Just don't put any kind of a load on it and you'll be fine - accelerate very slowly.

 

[demarpaint]

Somehow I think the back spec's ended at 1993, my 3.0 Vulcan Aerostar was back spec for 5W-20 as well. My 88 E-150 was not, maybe they arrived at 93 as the cut off year? I'd love to try it in my 88 as well but will use 5W-30 PP this time around until I get some more information.

Frank D

 

[Nickdfresh]

 

[rg200amp]

Originally Posted By: Nickdfresh
I wouldn't worry as your 5W-30 just sheared down to 5W-20 anyways. And if they used Motorcraft, then it's a synthetic blend. Most 5W-20s are probably syn blends whether they say it or not.


Yes, all 5w20s are some sort of synthetic blend

 

[Steve S]

Everyone seems to claim to get a 2 mile per gallon increase when switching to a 5w20 oil.

 

[brianl703]

Any 2 mile per gallon increase on my 1988 Mustang GT is due to changing the plugs, wires, cap and rotor...and maybe bumping the timing up to 12 degrees.

Incidentally, a vacuum gauge shows the engine to be in good condition. 19 inches of vacuum at idle which is from what I can determine the factory spec.

 

[Jaymus]

It'd be best to know what oil pressures you are getting while the oil is hot.

 

[brianl703]

The gauge shows the same reading it did when 5W-30 was in there.
I'm not sure about the accuracy of the gauge.

 

[Patman]

Originally Posted By: brianl703
The gauge shows the same reading it did when 5W-30 was in there.
I'm not sure about the accuracy of the gauge.


The oil pressure gauge in the Fox body Mustang is nothing more than a glorified idiot light! It just comes on and moves to one spot and stays there, and does not move up and down with the rpms like it's supposed to. In other words, it's either on or off, it'll show you when the oil pressure is at zero, but it won't show you when it's getting low, or when it's running lower or higher than normal due to a change of oil viscosities.

 

[brianl703]

It moves, but only slightly off idle. The sender was replaced because it was leaking, but it seemed to respond a lot more than replacement does.

 

[SevenBizzos]

Originally Posted By: Steve S
Everyone seems to claim to get a 2 mile per gallon increase when switching to a 5w20 oil.


In both of my Mustang clubs, various message boards, and here, I've never heard that....and I'm kind of glad I haven't.

 

[OVERKILL]

Originally Posted By: Patman
Originally Posted By: brianl703
The gauge shows the same reading it did when 5W-30 was in there.
I'm not sure about the accuracy of the gauge.


The oil pressure gauge in the Fox body Mustang is nothing more than a glorified idiot light! It just comes on and moves to one spot and stays there, and does not move up and down with the rpms like it's supposed to. In other words, it's either on or off, it'll show you when the oil pressure is at zero, but it won't show you when it's getting low, or when it's running lower or higher than normal due to a change of oil viscosities.


That is incorrect. The SN95 gauges were that way, the Fox gauges "worked", but they are inaccurate and the sender had a tendency to fail. I went through a number of them.

 

[OVERKILL]

Originally Posted By: brianl703
The gauge shows the same reading it did when 5W-30 was in there.
I'm not sure about the accuracy of the gauge.


The kind of pressure difference you are going to see is going to be SO small, that it wouldn't show on the stock gauge.

The difference between 0w20 and 5w50 in my '87 was only like 6PSI hot at idle.

 

[Patman]

Originally Posted By: OVERK1LL


That is incorrect. The SN95 gauges were that way, the Fox gauges "worked", but they are inaccurate and the sender had a tendency to fail. I went through a number of them.


I had two different 87 Mustang GTs and the oil pressure gauges in both of them were exactly the same, you'd start the engine and the needle would move to one spot and stay there, it wouldn't go up or down with the change in rpms like a real oil pressure gauge would.