Why exactly is "too damn hot" bad

[david lipman]

Hey all, as a somewhat paranoid owner of a 2.7 without front cooler (doesn't run too damn hot by the way without me being a total nut), I'm wondering what it is about a hot engine that causes damage. I know this may be a really dumb question, but I'm wondering anyway.

20W50 doesn't (shouldn't) break down at 250 degrees. Is it that the different expansion rates of different wearing parts causes excessive wear, is it fear of catestrophic cracking etc... Or could it be that 250 degrees is indicative of much higher temperatures elsewhere in the engine (where?)

[kstylianos]

20W50 doesn't (shouldn't) break down at 250 degrees.

Not necessarily true. Dino starts breaking down at these high temps (250-275) and synthetic starts breaking down at around 300 degrees. Thats why they say synthetic provides better protection at higher temps. The weight of the oil ususally does not correlate with at what temp it will break down. Thicker oil 'fills in the gaps' better than lighter oil, good for our air cooled engines that expand and contract quite a bit. When oil starts breaking down, it looses it effectiveness to coat and protect.

I'm wondering what it is about a hot engine that causes damage.

In general when things get hot, they expand. Our engines are designed to expand more than the conventional water cooled as its easier to control temps with a water cooled engine. Even though they are designed to expand more, there is a point where when the engine gets too got, the internals will expand beyond their designed tolerances and will start to grind against eachother (pistons and cylinders are common). 250 is marginal, anything more, shut down. The general heat cycling from cool to extreme hot can't be good either.

Or could it be that 250 degrees is indicative of much higher temperatures elsewhere in the engine (where?)

Everywhere. The oil temps you read are before they enter the cooling loop, and remember the oil absorbs heat the engine generates. If your oil reads 250, its a good bet your engine internals are alot hotter. The heads take a real beating when things get hot. Heat is a head killer

Ask me how I know. Been fighting high temps for a while and wondered the same

[TerryBPP]

Heat causes viscoscity break down, causing friction. Friction is an engines worst enemy. Think of a piston grrrrrrrinding against a cylinder wall, rings shear, vavles seize. Oh jesus make it stop!

[Chuck Moreland]

Read this:
http://www.elephantracing.com/techtopic/oiltemperature.htm

The other issue is thermal expansion which has a nasty habit of pulling head studs, especially true of 2.7 motors.

[david lipman]

very interesting. assuming it didn't cause massive oil leaks (synthetic), would the new M3 oil (15W-60) be a superior oil for our engines?

Extrapolating from the chart on the Elephant Racing page, it seems that an extra 10 of weight (like from 15W40 to 15W50) on the hot end is equivalent to 20 degrees worth of viscosity effect.

[john70t]

The ring end gap also closes as it heats up, and too much pushes it into the cylinder wall.

[nhromyak]

You will also tend to more easily pre-detonate (ping) the pistons at higher temperatures.

[SilverPoly]

I have the trombone oil cooler set up on my SC and it sucks.. not only that - it's ugly.

Anyways after I get my SSIs put on - I'm picking them up tomorrow- Thank You Pelican!!!!!!!!!

My next project besides wheels/tires are to upgrade to a late Carrera style cooler. And from what I understand upon thorough investigative research here is that Chuck Moreland is the man to go to. So with that said. I think it is 'wise' to upgrade to an external cooler. After all it's all about the oil flowing in these babies that makes them so special, no?

[UTKarmann_Ghia]

Here's a silly question: For us guys who dont have actual "numbers" on our oil temperature gauges, what do the 2 white lines indicate (temperature wise)? Mine usually stays right between the 2 white lines, but when I run her, she will get as high as the second white line (so far).

Anybody know?

[kstylianos]

For the non-numbered guages,

1st white bar = ~200 degrees F.
2nd white bar = ~250 degrees F.
Top Red = ~300 degrees F.

If you look real close, at an angle behind the guage rim, you can see the bars marked with their corresponding temperatures in Celsius. Once you convert these numbers to F., you'll get the above values.

[Joe Bob]

Originally posted by UTKarmann_Ghia
Here's a silly question: For us guys who dont have actual "numbers" on our oil temperature gauges, what do the 2 white lines indicate (temperature wise)? Mine usually stays right between the 2 white lines, but when I run her, she will get as high as the second white line (so far).

Anybody know?

Bet you if you look on the far left side of your oil temp gauge, you WILL see tiny little numbers that can only been seen if you have young eyes and put your head on an angle leaning toward the radio.....

[Joe Bob]

Oops, Charlie beat me to it.....my bad....

[Slider79SC]

So if I am tracking my car (two drivers even) but it never gets to the second white line on my gauge, am I to ASSume that my temperature range is safe?

[Wil Ferch]

I've often heard ( engine rebuilders on this list please confirm) that he upper-most area of the piston sees the most heat. This is understandable as its in the flame path of ignition. Accordingly, the upper-most piston ring takes a terrible beating, and cars running synthetic tend to have upper rings, and/or ring grooves in the piston in better shape. Temps here go to ( please confirm , again) 600 degF, as I recall. If correct, normal oils will coke and cake at this temp and syns will typically hold up better.
--Wil Ferch
PS---I've posted the temps of the various white/red lines on the un-numbered gauges for mid 80's gauges on the list before....can be approximated by 150/200/250/300 degF starting from the first white block ( not line) and going up.

[snowman]

Red line oil will out perform any Mobil 1 oil going, all the way to over 500 degrees F and it leaves no ash to clog things up like Mobil one does. If you have a balls out Porsche USE Redline oil, ask any real racer.

[Wil Ferch]

Snowman:
Intersting comments.... so you have a large scale lab and have determined this for yourself?...or you did "controlled" studies side-by-side on *many* motors to determine that Mobil 1 is junk in comparison? Interesting also in that published lists of various oils indicate Mobil 1 has no ash content..some others do. So how does this ash plate out when there isn't any?
I'd like to understand the basis of your comments... care to share?
---Wil Ferch

[rstoll]

There is another way to look at this too. There are a hell of a lot of SCs running around with trombone coolers and 140k on the clock. Looks like 20-50 dino and a trombone coolers works pretty good to me.