oil observation

Nov 8, 2022
helped my neighbor change oil in his 2002 GMC 6cy,4.2 engine,out was Mobil 1 5w-30 EP , I checked and was up to proper level,it had about 5k on oil since last change,vehicle has 115k on the odometer,,in was Royal Purple pcmo 5w-30,, (before we drained and ran engine i noticed engine noise),,after we put in new oil and drove around a bit ,,the engine was noticeably much quiter with the Royal Purple ,the same fram filter was changed out with the same (XG3506),apparently fresh oil can make a difference.
I heard characteristic light ticking from the OHCs in my first Volvo 'white engine' (the 5 cylinder ones).
I tried Royal Purple -I'm secure enough to admit that now- and the sound vanished.
'Twas no placebo.

I do believe the PO of that vehicle may very well have used cheap maintenance products as he, or someone he employed, trashed the PS pump with bad fluid.
This is my conclusion as to why some people "hear" improvements immediately after an oil change.
Some of it is a placebo effect, but I can admit that perhaps not always. But that pales in contrast to what I'll discuss next:

Oil temp versus engine temp at time of change.

Normally, the engine and oil are at/near the same temps. When you have a "cold start", both the engine and oil are cold. The clearances at all the various surfaces (bearing journals, rings in lands, etc) are all at one extreme of their condition, and that condition is not the normal operating temp. So any noises heard at start-up really are not worthy of concern unless there's an extreme, horrendous seizure of bearings going on. During "normal" operation, the oil is often the last thing to warm up, but at least during that "cold start" both oil and engine are at their resting starting point. We will ignore for now the topic of different metal expansion rates; that's another whole topic in itself. My point is that "cold starts" have both the engine and oil at an extreme that is not the intended operational condtions.

When at full operational temp, the clearances have normalized and the oil is at its desired viscosity. The oil thins (relative to the starting state of being "cold") and flows well, and presumably still provides that MOFT the designers consider adequate for the safe operation of the engine. The engine and oil came up to temp together (typically oil lags coolant temp by a bit, but they still ramp up at the same time though perhaps not the exact same rate).

But ...
When most all of us change oil, we end up with a unique condition that is unique in the OCI cycle. Most of us do exactly what the OEs tell us to do; we warm the engine with a drive cycle so we can get the oil up to temp; this has a few desirable effects:
- aids the speed of the drain cycle
- helps suspend any contaminants by mixing the oil immediately before drain
- reduces moisture (if you're doing to do a UOA)
So we then go about the OCI. The engine is at full temp and yet the oil is room temp (or there about). So the oil is MUCH thicker due to a large deltaT at this time you finish the oil change and start the engine. Then you drive the vehicle for a few minutes and marvel at how "quiet" the engine is. If your engine was around 200F at the time of pulling it in the garage, it may cool a few degrees as you change the oil. And the oil going in will warm a bit as it drains down the side of the internal block passage. But there's still probably a good 100F or more of temp delta the oil is presenting at your first start. This means the oil is much thicker than the "normal" operational condition, yet the bearings/rings/pistons have already gone through their heat-cycle size changes. So you end up with some unique condition that does not exist in normal daily driving during an OCI; it only exists at the first start/run of the OCI.

Now, this is an observational anecdote on my part. It's easily seen if your vehicle has an EOT sensor and display; some do. So next time you change oil, why not see how long it takes the EOT to come up in line with the ECT, and then see if you can "hear" the change relative to the oil vis shift due to temp shift.

So some of this might be a placebo effect, but some of it is real. But the "effect" is often inappropriately credited to some super-duper lube your brain wants to believe is "better", when the reality is that the deltaT of that unique start-up after an oil change probably is the main contributor to any "noise" change your ear hears and your brain perceives. If there's any placebo effect, it likely comes after the first several starts; you may have heard a legit noise change in the first OCI start, and your brain then induces that placebo into the next several starts.

We also have to admit that the number of variables in this topic are so numerous that it would be hard to design an experiment to quantify the results; real or imagined.

That's my perspective on this topic.
Engines are generally always quieter, right after receiving new oil.
Also, Mobil-1 used to sound louder with my engines. Not anymore! Ever since EP and Triple Action arrived, things are quieter underneath my hood.

When formulas changes, so will the perceived sound either increase (or) decrease.
I can only speak to the oil temp vs. coolant temp on my current car, a 2002 Jaguar XKR, as it has sensors for each. The engine is a factory S/C’d 4.0 L V-8.
Mechanical gauges have corroborated the following:

1) the oil temp is usually 16-20 degrees F higher than the oil temp

2) The oil temp will always reach normal operating temp of 195-220F before the coolant reaches its normal temp range of 180-200.

3) once the car has warmed up, the oil and coolant are never the same temperature. This mirrors my experience with other vehicles.

Has anyone ever had gauges that displayed a hotter coolant temp than the oil temp on a warmed up engine ? FWIW, I haven’t.

A meaningless anomaly ? Perhaps, you tell me.

Last edited:
Has anyone ever had gauges that displayed a hotter coolant temp than the oil temp on a warmed up engine ? FWIW, I haven’t.

I would agree, in general. Much of this goes to the topics of variability as I mentioned previously.
Newer vehicles have liquid-to-liquid heat exchangers (coolant to oil). These not only help cool the oil down, but also speed up the warming cycle.
Older cars with air-to-liquid (air to oil) coolers don't get that same warm up, nor do ones with no cooler/warmer at all.
Then you get into the topic of surface area to oil galley ratios. Long inline cylinder blocks have more "exposed" wall surface (to the ambient air) then does a V-type engine; that makes for a longer warm up. Blah, blah, blah ...

The LEO Dodge 5.7L Hemi Chargers we drove had a display tool in the IP menu. The EOT was typically 5-8 degF hotter than ECT when both were fully warmed, but EOT took longer to get there after a cold start. So the EOT rose slower, but rose higher.

Further, the older Ford 6.0L PSD (my neighbor's) would indicate EOT higher than ECTs; he had a scan tool plugged into the OBDII port at all times. Even prior to the cooler getting worse (the infamous clogging issue), the EOT was probably 5-7 degF hotter than ECT. The large sump sizes of light-duty diesels (14 quarts IIRC in that engine) took far longer to warm up than a smaller gas-engine would take.

My point is that generalities are fine, but they really don't help any one person ascribe a proven cause relatable to the oil versus noise issue.

My previous post was merely meant to illuminate the fact that the first start immediately after the OCI is a condition where the oil and engine temps are widely different; a condition not experienced at any other time in the OCI duration. That likely leads to some portion of audible difference, and when combined with a mental placebo bias, it's likely exaggerated in one's mind.
This is my conclusion as to why some people "hear" improvements immediately after an oil change.
Some of it is a placebo effect, but I can admit that perhaps not always. But that pales in contrast to what I'll discuss next:
Understood. My observations are from several days after the OCI comparing the used oil sound to the new oil sound in a hot engine. I only noticed these differences when changing oil grade.

Admitted, right after an OCI any oil sounds the best with cold oil in a hot engine.
We all carry a sound meter these days (aka smartphone) but nobody ever posts any numbers?
Or as we used to say in my working days, without data you are just another manager with an opinion.