Holding engine temp in hot weather

[TR]

Folks -- For those who might be interested:

Over the past couple of days my mechanics have been "tweaking" the electric fans and the new experiental air scoop.

I just came back from a 3-hours test spin in the car.  The top is down, and the Frigiking A/C compressor was running all the time...blowing very cold air with good volume based on the Spal blower unit.  In-town temp. was 95 degrees.  After approx. half hour of country road driving engine temp rose to ~21O degress.  Spent another half hour in stop & go city traffic...temp. held at 210.  Then let the car set in direct sun, A/C still running, and idled for 30 minutes...temp dropped slightly, to about 205 degrees.  Then drove off for a climb into the mountains; spirited, exceeding speed limit, but not pushing it too hard...steep, steady grade for 5 miles...engine temp did not exceed 210 degrees.  Came back and let it idle again, and it still held temperature.  The engine did not shut down during any of this, and the A/C was constantly running full blast.

I'm not declaring success yet, because ambient temp was only 95 degrees in the valley, 98 in the canyon, and 88 at peak elevation...But the engine is sure holding temp. better than it was before the cooling enhancements were made.  I hope we have more 105 degree weather before this summer is over so I can do a little more "stress testing", but I'm not counting on that.

Tom in Boise
'71 280SL 4-spd, signal red w/lt. tan interior, restored/enhanced

[mdsalemi]

Well Tom, having driven highway speeds down to Blacklick with the sun-a-blazing (but the temp holding at 180) and the ambient temperature about 90 degrees, I'd certainly be more comfortable in your CLK!

Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[TR]

Mike -- Here's the good news.  My wife was with me for this afternoon's run thru the canyon and up into the mountains.  This time, the first time, she said the old 280SL is as comfortable as the CLK500.  Coming from her that ain't no small thing!!

I believe what did this is the combined effects of; 1) the enhanced Frigiking performance (colder, more volume, better distribution), 2) the new fans inside the new seats, and 3) oodles of new Dynamat material which has made the car much quieter and almost rattle-free.  Of course, we were at less than 100 degrees today.  However, I already know the enhanced Frigiking will freeze us out when the soft top is up at 105 degrees ambient...no kidding, we have to crank it way down, and she likes to ride inside the equivalent of a refrigerator.

Hey, I noticed on Gernold's website that he has a lovely looking Frigiking for a reasonable price.  And when I had the recent honor of visiting Ranchomerced I saw that Mark had come up a very impressive alternate "stealth" A/C concept, using the heater fan as I recall.  You might consider something like this to make your drive to Joe's place a little more comfortable/civilized next year...or not...

Tom in Boise
'71 280SL 4-spd, signal red w/lt. tan interior, restored/enhanced

[TR]

Mike -- Oops ... I forgot to mention another key contributor to the car's comfort is the wind-screen behind the seats.  Really does the trick I believe.  As I recall, you recently tried one at Joe's event, yes?

Tom in Boise
'71 280SL 4-spd, signal red w/lt. tan interior, restored/enhanced

[ja17]

Hello Tom,
Try turning on the heater and fan full blast to see if this lowers the temperature. This will test to see if  increased radiator area along with more air flow is needed to lower temperature. If no noticable drop in temperature, you may need higher  volume of coolant circulated. Maybe polishing the impellers on the water pump could help? Just some wild thoughts.

Joe Alexander
Blacklick, Ohio

[norton]

If Joe's test shows that you need a bigger rad, maybe the oil cooler could be relocated to the wheel well to make room for a wider custom radiator.

Mike Halleck
Chesterfield Mi
71 280SL
68 250SL (parts car)
94 E320 Coupe

[TR]

Joe -- I've not tried the 'heater-on' thing since these new mods have been made.  Good idea; thank you ... I'll do that on the next hot run.

Any opinion on holding at ~205-210 in those traditionally tough conditions (city stop & go, prolonged idle, mountain climb) I've described?  Those numbers were better than I'd seen before, so I was somewhat hopeful.  (however, yesterday wasn't a 110 degree day either).

Mike -- Thanks to those recent great & helpful inputs, we've added the idea of relocation of the oil cooler to our contingency plan list.  Our back-up list now includes:
-  The possibility of a larger (X & Y axes), custom radiator,
-  Relocation of the oil cooler (to make room for above, and to reduce heat load seepage into rad.),
-  The possibility of adding small "helper" radiators, with fans, under each front wheel well.

Any comments/thoughts/additions/deletions on these contingency ideas would be appreciated.


Sure hope we have some more 100+ weather here, because in the event we still need some addt'l cooling capacity it'd sure be nice to do some of that work over the winter.  As a point of comparison, however, I took the CLK500 out last week (100+ day), and it also increased to a little over 200 degrees (maybe 210) in stop & go city traffic and when I did my mountain climb thing.  I don't believe I've mentioned the results of that CLK500 comparison-drive before.  As the old 280SL starts to reach the passenger comfort level and engine temp. holding capability of a new M-B I'm becoming somewhat encouraged ... but don't feel I can yet declare victory over the terribly aggravating old problem of a '71 280SL with A/C overheating.


Tom in Boise
'71 280SL 4-spd, signal red w/lt. tan interior, restored/enhanced

[J. Huber]

Am I doing the math right, that 210 is about 98 degrees C? If so, wouldn't that be markedly higher than "normal" driving temperature? Why am I under the impression 80 C or @ 180 F is where you want to be? What am I missing?

James
63 230SL

[J. Huber]

I may have figured it out on my own. I just looked at my gauges. The white square beyond the 80 would probably be around 100. Then going up, the red square is about 110? ... So to have your car level off and not exceed the 100 mark for a longish period of time would be a victory of sorts given the fairly extreme ambient temperature. Am I getting warm? (of course Pun intended...)

James
63 230SL

[TR]

James -- Good stuff...I agree.  And I don't think you're missing anything.  We can tell the car seems to "naturally want" to run at 180-190 degrees F.  But for a little insight into what we're up against, here's some words straight from pages 28 of my 280SL Owner's Manual:

"...During hot weather or mountainous driving, and expecially during city driving in vehicles equipped with air conditioning, the temperature may rise to 239 degrees F (115 degrees C ... note that's the "red" mark).  If the boiling point (239 degrees F under pressure) has been reached, the vehicle should not be driven for any length of time.  Coolant loss by boiling has to be replenished..."  

So, it would seem to me that M-B was clearly warning us, especially those of us with A/Cs, to "watch it".

James, I'm not certain about this, but have the impression that cars with A/Cs, and perhaps late model 280SLs in particular, have a tendency to run above 180-190 degrees IF the A/C compressor is running flat out all the time and when idling for prolonged periods, or in stop & go city driving, or leaning into it when climbing steep & long mountainous grades...especially with the top down and ambient temperature is 100+ F.  I would/will be one happy camper IF we're ever been able to do all of that and have the engine hold a rock-solid 180-190 degrees F.  I believe the real challenge here is to have the top down, running the A/C compressor non-stop hours at a time, in ambient temperature conditions of say 110 F...and in all of those driving conditions I've described (ie, prolonged idle, stop & go, and long & speed climbs into the mountains).  I've recently confirmed not even a new CLK500 cabriolet runs at <200F under such conditions ...And when all of the CLK500's fans kick in at the same time it sounds like you're standing next to a propeller-driven aircraft (which I kind of like!).

But over the coming winter I think we'll probably do at least of couple of those back-up ideas.  Wouldn't it be loverly if we could then keep it at <200 degrees F in any and all conditions.  In fact, I have a long term plan to take the car into Death Valley in the hottest period of the year just to see what we can achieve.  Besides, it's been too long since my wife and I have stayed at the Furnace Creek Inn there  Great old spot, and with a pretty good wine list too!

Tom in Boise
'71 280SL 4-spd, signal red w/lt. tan interior, restored/enhanced

[glennard]

quote:Originally posted by J. Huber

Am I doing the math right, that 210 is about 98 degrees C? If so, wouldn't that be markedly higher than "normal" driving temperature? Why am I under the impression 80 C or @ 180 F is where you want to be? What am I missing?

James
63 230SL

What is the thermostat temp

[Benz Dr.]

You're climbing a long grade right? How high up is the highest point in elevation?

Part of the problem is coolant teps but the other part is oil. Almost half the cooling is done by oil and while sitting there's almost no air crossing the oil pan with the engine running. This is why most engines will cool once you pick up speed as long as there isn't something else wrong.
 Very high performance engines often go to dry sump to use oil as a coolant as well as being able to lower the engine or hood line.
Think more oil and/or oil cooler, think 300SL.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org

[George Des]

Tom,

I agree with Dan's cmt regarding the oil. Perhaps the oil pan can be modified to have more surface area by TIG welding on some fins that will increase the effective cooling area of the pan. Just a thought.

George Des

[TR]

Oops, I just noticed I used the "less than" sign in front of 200 degrees F for the CLK500.  That was a typo; I meant >200.

But, yes, thanks.  Part of our further enhancement plan is to give it a go with a remoted, higher efficiency oil cooler, as well as to make certain we've got the latest pan (of the type Joe was talking about), and then consider the possibility of also "finning" it.  We'll do this over the winter, if for no other reason than to have cooling capacity aplenty when next summer roles around.  This effort will likely involve installing a wider high-capacity radiator ... as well as trying out another A/C condensor too.

Sorry about that goof with the < (less than) sign.  But the point I was trying to get across was that the current cooling mods on this '71 280SL now has it performing similar to a new CLK500 in terms of engine temps…meaning they both run a little over 200 degrees during  those difficult conditions I've described.

It really would be a hoot to have these addt'l mods completed early enough to get the 280SL to Death Valley next summer in order to try out the collective cooling enhancements when the air temp there is over 120 degrees.  And to enjoy the facilities at the Furnace Creek Inn again.

Tom in Boise
'71 280SL 4-spd, signal red w/lt. tan interior, restored/enhanced

[ja17]

Hello,

Maybe Mercedes agrees with Dan and George because the latest version of the M130 engines in 1972 (after the W113 production) had increased oil capacity and fins on the inside of the oil pan. Everything bolts right on the old engines. A special rubber pick-up is attached to the oil pump pick-up for the deeper pan. So you are probaly on the right track here also Tom.

I had added an oil temperature guage to a M130 engine one time. It was very interesting to watch as it varied from the coolant temperature guage.

Joe Alexander
Blacklick, Ohio

[Benz Dr.]

The new oil pan is only slightly deeper by 7mm. The ribs are or identification I think.

The fins are inside the back on the pan and is really a widage tray to help pull oil off the crank. Probably some cooling help.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org

[George Des]

Yeah. My suggestion for fins was meant for them to be on the outside of the oil pan so they would offer more surface area to the ambient air flow. Technique is used alot in cooling electronic parts. There may be additional areas where this "finning" may help--perhaps the bottom tank on the radiator with soldered on copper fins--or a baffle with holes on it attached to the bottom tank that would direct some air flow up from under the car. Realize these may only be effective while moving, but every little bit may help.

George Des

[ranchomerced]

Speaking of oil temperature you will need to consider a problem that the gullwings and roadsters have since they have a very high capacity dry sump and large oil cooler. If the oil temperature never gets above 145 degrees or so they have a tendancy for oil dilution by gasoline. We solve this problem by by passing the cooler and reducing the quantity of oil. You can have too much of a good thing with the oil temp solution. Mark

[Benz Dr.]

A 300SL engine and a 113 engine is very different. The oil pan on a 300 holds about 4 liters and the rest is held in the reserve tank. The entire system holds about 12 - 14 liters. The engine has two oil pumps - one for oil pressure and a dry sump unit that sends oil back through the tank. I'm not 100% sure how it all works because I only had the head off and didn't go ner the bottom end or oil pumps. Fuel dilution is very common on these engines and can be caused by low oil temps but is also caused by incorrect jetting at the air control valve and and improperly adjusted cold start slide.
The 300SL egine has no throttle linkage going to the injection pump and has only a vacuum line running to it that is fine tuned by air jets at the air control valve. Although not too difficult to set it can be tricky and take a while to get right.
The oil cooler on a 300 is a bit larger than the oil cooler on a 113 but it's more likely the volume of oil that makes the bigger difference. These cars have oil temp guages on them which are similar to a 190SL temp guage. The one I drove never went very high in the mostly cool spring weather I drove it in. During this time we used a thin sheet of metal to cover the back of the cooler until it got warmer outside.
In warm weather it got so hot inside of the car that I took the shield back off. Oil coolant temps never got higher than about 60 degrees C.

Can someone tell me the elevation of Boise Idaho? How high are the mountains in the area?

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org