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MG TD TF 1500 - Chemistry Question about oil

I am not concerned about winter weather. My garage is heated and the car is never out in the colder weather.

I am trying to compare two different oils. A straight SAE 30 versus 20W-50. Which will be the heavier oil for my operating conditions?

My understanding is that the W in 20 W stands for winter and in the colder weather the oil will perform initially as a 20 weight and as the engine oil temperature rises it performs as a 50 weight. It seems to me that at the temperatures I operate the 20 W 50 would be a lot more viscous then a straight SAE 30.

My goal is to use the most viscous oil that I can to help seal leaks without harming the engine.

I have read what I could find in the archives but I would appreciate any and all advice on the topic.

TIA,
Mort
Mort 50 TD

Mort,
While what you say is true, remember that the 50 in 20W50 specified the viscosity at 210 degrees F. But during initial startup, you want the oil to flow easily at the ambient air temperature, that is, before the engine comes up to its operating temperature. If it doesn't, there will be a lack of oil flowing and thus wear occurring.

Stick with a good quality of 20W50. Castrol or Valvoline are two good choices. I've been running Castrol 20W50 in my TD for over 100,000 miles with no engine problems (that I haven't caused).

If you have leaks, fix them, not try to do something which may cause further problems down the road.
Lew3

When the ENGINE is cold it's like a straight 20 weight.
When the ENGINE is hot it's like a straight 50 weight.
When the engine is hot outside temp does not matter since the thermostat controls engine temperature.

When the engine is cold and has been sitting then outside temperature does matter.

Jim B.
JA Benjamin

The 20W - 50 oil should have the viscosity of an SAE50 oil at normal engine operating temp, which is higher than the viscosity of a straight SAE30 at the same elevated temp. Its physics.
Dave H
Dave Hill

It essentially is a 20W oil with modifiers added that keep it thicker than regular 20W would be when hot. Idea is it performs like 50W against high temps in the engine, yet is thin like 20W on startup.

Anyone know the typical XPAG engine oil temp range with the engine in stock form and no extra oil cooler? I often wonder if 30W may not be more appropriate, unless of course the engine ever typically runs hotter than 30W can handle.

One advantage of single weight oils is that they cling to vertical surfaces of the engine better than multi weights do, and if the engine sits long enough between startups, that could be a problem. Then again, the multi weights have quite a few advantages of their own.
D mckellar

All of the above is true. The way it works is that the oil starts out as a 20 weight oil, or maybe a little thinner. Viscosity improvers (VIs) are added, which are molecules that are curled up and small when cold but open up when hot. That means that they don't have much effect on viscosity when the oil is cold since the curled up molecules flow easily, kind of like small spheres. As they open up with temperature they get much longer and bigger and entangle with each other and other molecules so that the the oil doesn't flow as easily, hence the viscosity goes up. By adding the right amount of VI the oil can act as a 20 weight when cold and a 50 weight when at running temperature. Clever eh?
Ron Coates

Mort would you send me a note to dorydd0555 at aol

I'd like some feed back about a TD part on your car.

thanks

LaVerne
L E D LaVerne

This thread was discussed between 11/08/2016 and 13/08/2016

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