So...looking at my weatherbug right now, it says it's 100 degrees in Austin. Are you saying that if I take a trip from Austin to Ft. Worth (160 miles) travelling at 70mph (2900 - 3100 RPM) I'm in full boost and could possibly melt my pistons?

I can make this trip and the coolant temp will typically ride from 85 to just under 100 celcius, depending on hills.

Danger zone?????

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1984 W123 300D Gone to the wrenchapart
1972 W108 280SE 3.5 (sold but not forgotten)
1986 Buick Grand National 3.8l Turbo (86k miles)
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Brian,

Answers:

1) 105ºF, 7% grade, ~9 miles
2)I was more concerned with it NOT going higher than 1100ºF and didn't notice stabilization that much (or don't remember well enough ).
3)110ºC which resulted in close look at cooling system and a new radiator. I can't get it over 94ºC if I try now.

The off-road boys who do longggg competitions use 1200ºF as a max, I believe. This site says 1350ºF is a max for MOST (not neccessarily MBZ) turbo diesels. http://my.ais.net/~hypermax/products.htm

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Did anybody notice the glowing manifold and turbo in the C-III video? I'd bet that was a tad over 1100* but they didn't have to worry about lasting 300K+ miles

High boost is not indicative of high EGT's. If you have stock fuel settings you don't need EGT or boost gauges on a regular basis. I prefer the 270* sweep gauges over the 90* ultralight/two cycle type of gauge as I believe the greater needle sweep offers higher resolution. www.dynotune.org and www.isspro.com offer nice gauges. The former offers a digital key-fob sized gauges that should be very easy to mount. I don't see how a stock MB even held wide open for extended periods would have any problems. They are well designed and conservatively fueled. Mess with the pump and all bets are off, you need gauges ASAP. The generally accepted limits for pre-turbo EGT's are 1250* max sustainable IF you have a factory turbo setup. 1100* if you are running an aftermarket kit on a previously NA engine. I would say 1100* is a good conservative max. RT

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At 70 mph turning 3000 rpm, you are not in full boost unless you are going upgrade. So, the answer is no, you can never melt your pistons going from Austin to Ft. Worth, AFAIK.

Now, if there is an extended grade, and you have your foot almost all the way down (past 2/3) for two, three, four, five, minutes, then the EGT's will climb up to a dangerous level.

See the answers from jbaj007. He had a 9 mile, 7% upgrade in 105 degree ambient conditions. This is the worst possible situation for a 617. The exhaust temperature rose to 1100 deg. and he was concerned with keeping it below that, so, I would presume that he had to slow the vehicle down.

If you had no gauge, and tried to maintain 65 mph for 9 long miles on a 7% upgrade, you might do some damage.

Thanks for the info. It appears that you were concerned with it climbing over 1100F. Presumably you had to slow down, somewhat?

Will it stay at 94 deg. C. on that same 7% grade with the a/c on? If so, that is fantastic. Please do tell the secret to this. Neither my 603 or 617 will stay below 100C. if under heavy boost with 80-90 ambients. In fact, tonight, the 603 would climb up to 97 or so under boost, without a/c! And it has a fairly new radiator!

It is easy and worth it.

boost controller install...

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Brian,

Haven't run Sherwin Grade (outside of Bishop) in that kind of heat since doing cooling system improvements. I'll run the Grapevine sometime soon this summer, though, and report.

First, I must explain that I really have a frustration problem with anything (Me, car, office, house, weather) not being temperate. I have ended up replacing the radiator on most every used car that I've ever kept. This has always proven to be the end solution after fiddling with flushes, thermostats, fans, et. al. This is only what worked for me; not, particularly, what I recommend for everyone. In an IDEAL engine cooling system the temp should never rise above the thermostat's full open temperature. Picture a radiator the size of Rhode Island (this is only a visual exercise ) and the 300SD thermostat ....87ºC starts to open....94ºC fully open. In this imaginary closed loop system, the temperature of my engine should never be anywhere but between 87ºC to 94ºC.

In search of the real life approximation I've done the following:

1) citric acid flush then new Behr radiator.
2) new water pump.
3) checked and/or replaced water hoses.
4) checked current thermostat (and it's back-up in spare parts bin) with hot water/candy thermometer to insure it is in spec and opens smoothly.
5) drilled/tapped/refilled viscous clutch with 6000/10,000 CST silicone oil.
6) shortened actuating pin under bimetallic strip on viscous clutch by 1mm. to open chamber slightly early on temp climb.
7) drilled, tapped thermostat housing and wired in adjustable temp control for aux. fan, so I can set the temp that the fan comes on, and relayed it to come on whenever airco is on as well.

With all of this, the engine temperature has been perfect, ....but.... it's been relatively mild this summer where I've been driving. I haven't hit the Grapvine, Sherwin grade, Mohave or Ridgecrest in daytime heat recently. I have driven the Valley (both San Joaquin and San Fernando) a fair amount in 100ºF and nary a blip above spec.

I know that MBZ says anything under the "RED" is OK, and I don't want to argue that point here. This is what I've done and it works for my MB. FWIW

You don't want to know what I've done to the A/C to keep it nice and cold

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

jba,

That is excellent. You have really gone and done everything necessary to have the system at perfection, and, clearly, you have the results to show for it.

Since my radiator is close to new, I believe that I need to look at the water pump and the viscous clutch.

Do you have any suggestions on testing the clutch? Is there some sort of standard to determine if it is within spec with regard to engagement at high temperatures?

And, if not within spec, any tips on refilling it would be greatly appreciated.

Test is in the FSM and consists of getting it hot enough to couple, and listening for a roar. I could never tell well enough due to stupidity or deafness . I use the shade tree test of running the car around with a piece of cardboard over the radiator until it's a little hot, parking it while still running, and shutting off the engine with the shut off lever under the hood. If the fan freewheels after stopping the engine, I figure the clutch isn't hacking it. More "feel" than science, but it's the best I can do. Be sure and remove the cardboard afterwards (don't ask )

Based on that test, I've filled my clutch and two on friend's cars, and the clutches all took a lot of silicone oil and didn't freewheel as much afterwards, so it works for me.

Modification that I did is described here Write-up on fan clutch repair and TomJ has great pictures of him doing it.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)