Infrared temperature gun readings? engine seems to run hot 69 280sl

[cattledog]

Hi Everyone,
My engine always seems to run hot at least according to the gauge on the dash, especially going up long grade type hills.   I watch the gauge very carefully as I certainly don't want to overheat the engine.  I have the fan shroud and the radiator doesn't look too gunked up inside.

Anyone have any reference info on acceptable temperature ranges at various external locations on the engine?   I have an IR temperature gun with a laser pointer that I often use for checking temperatures at various points on my marine diesel engines - its a very handy tool with many diagnostic uses.

I would even consider putting a secondary audible temperature alarm on the engine.   Accuracy can suffer on old gauges with old wiring out the sensor.   With the consequences of an real overheat being so dire, an extra sensor could provide extra protection.

Chris

[alpina]

Hi Chris,
I for one would be interested in the results it anyone else would take some readings. I was hoping someone would
help out following on from this topic https://www.sl113.org/forums/index.php?topic=23973.msg171850#msg171850
but no luck. If you read through you will see my temps and where the needle sits on the gauge.
regards

DM

[scoot]

When I used an I/R gun on my engine block it came out with the same temp as the gauge read.  On my Fintail I had a bad gauge that ran way high.  You can test the gauge by placing the sender in boiling water and seeing what the sender reads.

[cattledog]

Thanks Scoot.   Yes, I have used a "candy thermometer" in other settings to check temperature sensor readings while the water heats up.  That's a good way to check the sensor.

I'm more talking about trying to understand what readings are "typical temp ranges" at a few sites on the engine and cooling system as a means to help troubleshoot cooling or other issues.

On my diesel engines, you can often tell which cylinder isn't firing properly by taking a temp read at the exhaust manifold site nearest that piston.   There are plenty of things these IR guns are handy for.

Chris

[Mechudo62]

Hi everyone, I have a 1970 280SL that exhibits the same rise in temperature on steep grades. Another Mercedes-Benz Mexico Club member´s 1969 280 SL behaves the same way. We have both made sure to overhaul the entire cooling system in our cars. In my case, I installed the factory cooling kit from the technical service bulletin, brand new radiator, wáter pump, fan clutch and thermostat which helped some, but the needle still creeps toward the hot range on grades and also in heavy city traffic. I have wondered if the dash instrument is to blame, or the nearness of the sending unit to the radiator or to the hood´s hot metal surface that adds to the real cylinder head temperature. We have checked timing and fuel mix and our cars don't run lean, maybe a little rich, which is not cause for engine overheating.

I have never heard of 230 or 250 engines with this problem.   A possible conclusión is that 280 engines do have a tendency to run hot due to the fact that the increased displacement took up space from the cooling tanks on the engine block, which is why the factory installed an oil cooler also. I have heard of some 280 SL Pagoda owners adapting a supplemental electric fan from a later series 450 with mixed results, but have not tried yet. Has anyone experimented this fix...? Its hard to accept Mercedes-Benz actaully built cars with marginal cooling systems,  there may be another factor we are overlooking... We would love to hear from other Pagoda owners if they have had this problem and how they fixed it.

[scoot]

That's interesting on the diesel engine and IR gun - clever.

IMHO it should run at 80 C or 175 F, or whatever the rating is on the thermostat.  The cooling system should be able to keep the car cool while in motion to the temperature on the thermostat.   If you see it going up higher than that on level ground while moving there is something wrong.   If it goes up a little higher than that while going up a long hill then that's probably ok. 

[scoot]

Its hard to accept Mercedes-Benz actually built cars with marginal cooling systems,  there may be another factor we are overlooking... We would love to hear from other Pagoda owners if they have had this problem and how they fixed it. 

In that era, I think Germany built cars designed for German weather, hence the lousy AC units in older German cars.  That could also apply to the cooling system.

[Mechudo62]

That´s righr Scott, that could very well be the cause of hot running 280´s... They were simply not engineered for hotter climates or the heavy traffic conditions of today´s roads. That´s why some people adapt electric fans.

[alpina]

So Scott, you are saying that when your gauge reads 80c your IR gun reads 80c on the engine?
In my case the gauge reads midway between 80c and the next white square (100c)
Measuring temp at the engine I have readings between 72c-79c. Would that mean the gauge is reading
High?

[scoot]

Gosh, I could be mistaken.  My recollection is that if I placed the IR gun close to the side of the hot engine it actually matched the gauge temperature.  But it was a while back and I could be remembering incorrectly.

[cattledog]

Some good discussion here.   Avoiding overheats is a BIG concern on boats when it can cost $50k or more to rebuild a large marine diesel after a serious overheat event. 

My car is still torn apart waiting for new brake calipers but I will take some measurements when I get back on the road hopefully in 2 weeks or less!   

I think taking some baseline measurements would be helpful, especially before I do anything "extra" like add an electric fan.

My german bikes (KTM's) are also hot blooded - they have electric fans that kick on and they would certainly both overheat if they did not have this added cooling capacity.   

I would really like to get my cooling system running strong enough to never see that darn needle creep up.

Chris

[Jonny B]

Chris,

On my 280 SL, I see the same slight creep on a long grade or idling in traffic on a hot day. I also have had the radiator recored (three rows), a new fan clutch, and a new thermostat. I keep an eye on it, but it really has never been a big problem. It has never gone over the last white square.

I also have an IR gun, but have not been quite as methodical as you state. I think I will do that.

Once you get your car running, you should plan to come up this way (San Marcos) and we can do a cross comparison.

BTW - on my 250 SL the temperature stays below the 180 mark, pretty much no matter the condition.

As others have stated, the 280 SL does have a tendency to run warmer. Less radiator (now the oil cooler is on the side of the radiator) and the changes to the block to make it 2.8 liter.

[cattledog]

I would really like to know if these cars had a reputation for overheating when they were new?    Maybe minerals or other crap build up in the engine too that make cooling more of a challenge as these cars age.

Jonny, It would be fun to meet up and compare temps.   

There are systems for recording temperature and other engine parameters, most race cars have these systems and there are less expensive systems available that radio controlled airplane hobbyists use (probably other types too).   it would be neat to get "some data" on this whole problem in order to try and develop a logical basis for trying certain changes or upgrades.  Coolant temperature, cylinder head temperature, speed, outside temperature - recorded over a series of  hills.

Another answer might be to ignore the whole needle creep problem.  I found a post elsewhere that mentions some text in the MB owners manual- see page 31 which says: " During hot weather the temperature may rise to 239F (red spot on gauge) without causing concern".    Lol maybe this idea was sort of OK with a new car, but the notion of pushing my nearly 50 yr old car to this level makes me cringe.

How about an electric  fan that tries to really target the oil cooler?   The oil cooler seems to be "off to the side" and not really in the air flow of the engine fan.   Oil is a good cooling medium - lets not forget all the famous air cooled Porsche's which of course are actually oil cooled.

Amazes me that the needle NEVER moves beyond the usual position on my modern Toyota truck.

[mbzse]

I would really like to know if these cars had a reputation for overheating when they were new?

The rear cylinders (5&6) were slightly prone to overheating when car was run prolonged on the Autobahn at high speed. Of course, one must consider that the oils of 50 yrs ago were not as sophisticated as today's motor oils.
   

Maybe minerals or other crap build up in the engine too that make cooling more of a challenge as these cars age.

You are on to something here. Due to 50 years of operation with various degrees of maintenance there may be scale buildup inside the engine block of our Pagodas. See picture attached showing a block sliced open (not a M-B).

As a comment, the temp needle in my Pagoda 280SL never moves once it has reached operating temperature. However, I do not live in a desert climate.

[neelyrc]

I would really like to know if these cars had a reputation for overheating when they were new.......

....Amazes me that the needle NEVER moves beyond the usual position on my modern Toyota truck.

I have never experienced any overheating on my 280 SL from new (knock on wood).  Now at 50k miles, about 50% in Alabama.  Pretty warm but not desert.  As Hans indicates the needle never moves once it reaches operating temperature.

Same for my modern(?) Toyota truck also, now at 110k km (2004 D4D Hilux).

[cattledog]

I have a snake camera and will try to see how much scale build up there is at least near the thermostat.   I know cooling can be affected radically by contaminants on the surfaces of metal.   For example, an oily film on metal can reduce heat transfer with coolant and it makes sense that heavy scale could too.  I know my car sat unused for long periods of time and that's an invitation for scale to develop as the additives in all coolants "fall out" after many years and can become gunk and other crap that is adhered to parts in the cooling system.

Seems like the 280sl cooling system was already marginal even when new.  Add some scale and other problems to the system over many years and maybe that invites the "needle creep."

On my marine diesel engines, I rigged up a recirculating pump and cleaned out the cooling system scale by running a 50/50 muriatic acid / distilled water mixture through the fresh water side of the cooling loop.  A lot of crap came out when I was done and the passages were much cleaner afterwards.   Whether this type of flushing can be harmful to seals and gaskets is an important question, I have never had any leaks or problems as a result (so far lol).   

Large marine diesels are very tough and do not have any aluminum in them at all, at least mine don't.   Talking about engines that weight more than an entire 280sl here.    If I was to try a cooling loop flush / clean  on my 280sl, I would use diluted vinegar after more research.   Googling "vinegar cooling system" yields quite a few results.   You would probably have to remove the thermostat and maybe try to bypass the water pump if you wanted to do this type of cleaning on a 280sl. 

Chris

[KenBourque]

When using an infrared gun to measure temperature, the surface must not be reflective such as an aluminum head or a higher temp will be recorded.  Hence, I painted a little flat black spot directly the temp sending unit to get a more accurate reading.  The gun and the dash instrument now read pretty much the same.

[Tyler S]

Amazes me that the needle NEVER moves beyond the usual position on my modern Toyota truck.

This is because most if not all modern cars dash gauges are fed substituted data from the ECM. There is no direct connection to the sending units. The engine could very well be getting hotter on a steep incline. But if the ECM determines it is within normal parameters, the gauge will not move.

And here lies the problem. A lot of us are so accustomed to our daily driver that we use them as a baseline. Needle creep under severe load on older cars is not out of the ordinary. Not saying that some cars wont have real issues, just somthing to keep in mind.

Also, if your gauge is reliable and reading hot, you can most likely rule out block scaling. The coolant would not be getting hot if heat was not allowed to pass to it from the engine. Steer twards coolant flow and radiator issues instead. Expelling that heat is whats important.

[Rolf-Dieter ✝︎]

JFYI

On my 280 SL 1969 I experienced overheating issues in 2013 and after changing the fan clutch and a re-core of my radiator I no longer have issues.

Dieter