My 6.9 overheating

[Styria]

As Sydneysiders would know, we have experienced our fair share of quite hot days - many times at least 34 degrees centigrade, but even hotter days when temperatures have reached more than forty degrees.

Gleaming Beauty, my 6.9, is a daily driver and as such, the mechanicals and cooling system have been exposed to these conditions. How many others in this group use their 116s on a daily basis and how do you find the cooling system coping with these heatwave conditions ? For instance, yesterday with temperatures in the West being close to the 38 mark, and with heat coming off the road surface like you wouldn't believe, I saw the temperature gauge needle just going over the 100 mark - normally 100 can be reached quite quickly (perhaps disturbingly so), but seldom will the needle go over the 100 mark.

Naturally, the auxiliary fan being of the 85 centigrade version, is forever working away quite furiously, as well as noisily. In fact, the din coming from it , again can be quite disconcerting. The question I have, or the opinions I am seeking from others, should one be concerned with these temperature readings ? The cooling system, to all intents and purposes, is in excellent condition, and I am still running an 87 degree thermostat. There appear to be no issues with the way the car is performing, but I just wonder to what extent the cooling system can be considered to be only just adequate to cope with really hot climatic conditions. Regards Styria

 

[WGB]

I had a 126 300SE 20 years ago that did that and I had a few problems with a cracked plastic radiator tank.

It was settled by a new fan hub and a lower thermostatic switch for the electric fan.

My 6.9 appears to have a 75 degree thermostat (although I am not sure about that) and runs just under the 80 degrees in winter and at 85 degrees in summer with a bump up to 90 (or a little above) degrees when climbing hills at 38+ degree heat.

I have never owned a 116 or a 126 that was really happy idling in traffic on a hot day.

I know you do not like the 75 degree thermostat but if you have a good functioning Auxillary air valve it should be well closed by 75 degrees and my car doesn't have any winter problems that I can see with running a little cooler than expected.

The other option is to change the thermostat between seasons.

Merry Xmas and thanks for the card.

Bill

 

[Michel]

I drove my 690SEL on a 40C plus day and found that the temperature didn't go past 80C (or so).

The air conditionning was not freezing cold, but we survived with a bit of fresh cool air blowing

NB:

My radiator was recored a year ago

 

[TJ 450]

I'm driving my 6.9 every day now, and in this weather, the temp creeps up to 90 and just over. I have wired in a manual override for the thermo fan and that seems to help.

I know you have a recent radiator core, but it may be worthwhile descaling the system.

Tim

 

[B13]

Mine get a little hot under the collar too but from my previous experience with other W116s this is pretty normal and as long as the temperature stabilises and starts making its way down once you are moving then the cooling system is probably OK.

Mine regularly hits 100C idling in traffic with the a/c running on a day like today (36 degrees in Melb) though I've had it as high as 115C and it didn't make any tell-tale overheating signs like heat-related pinging, bearing slap, loss of oel pressure, rough idling, misfiring, exhaust smoke, steam out of the engine bay or hot-metal-type smells. Rather than pull over and switch it off I drove a different way home and the temp dropped back to 100C where it stayed until I got home. When everything had cooled down for a few hours I expected I'd need to top up the coolant and possibly have to change the blackened (burned) engine oel but it hadn't lost any coolant and the oel was still clean.

I.

 

[Styria]

I drove my 690SEL on a 40C plus day and found that the temperature didn't go past 80C (or so).

The air conditionning was not freezing cold, but we survived with a bit of fresh cool air blowing

NB:

My radiator was recored a year ago

Michel, that's staggering - that temperature reading defies all logic and I'll tell you why - it's a theory that's been proffered (get hold of THAT word !) by a good friend of mine - another 6.9 owner. Now, he maintains that if you fit a colder thermostat, i.e. in other words, one with a lower degree specification, the water circulates through the system too quickly and the coolant that's in the radiator, doesn't stay there long enough to be cooled properly whilst you're on the move.

I know from experience that his opinions are likely to be off beam somewhat, but sometimes it's uneconomical to argue about issues, especially if you're not totally familiar with them, or you can't talk with authority.

I have fitted an 87 degree thermostat to a 450 (should be 79 degrees) and it was hopeless. The car just ran far too hot. Mind you, I do think that if your 6.9 does not reach proper operating temperature, you will use more fuel. I'd be interested if you've ever done a fuel consumption test and what the result was or would be. Regards Styria

 

[BenzBoy]

I suspect you are quite within normal Styria (well I refer to the car here) and unless you have obvious signs of collant loss through expansion or poor running, I would not worry. What you report is within the range specified by the handbook but we have become used to modern cars that never rise above the normal operating temperature.
Why not run an infrared temperature probe over the radiator and engine to see if there arre any hot spots and to check if your gauge is accurate?
Regards,
Benz-boy

 

[WGB]

The larger mercedes engines (6.9 seem to be an exception) all ran at 80 degrees until the second series 126 when the thermostats were changed and the gauges all read 85 degrees.

I remember having this conversation with the Service Manager at Diesel motors in about 1990 when my 300SE was always running hot in traffic.

If you use the correct coolant and if your radiator cap is good they are supposed to be safe up to 120 degrees - read the owners manual it says that the car may go up to 120 degrees when travelling through hilly country in hot weather.

My nerves wouldn't stand that but I would think the odd run up to 100 or 105 is pretty inconsequential and often when the motor is started after a short ice-cream stop on a hot day the gauge can temporarily be near the 120 mark until the coolant starts to circulate.

My ML's don't have a Guage but you you can call up an electronic one in teh dash and neither moves at all past 85 whatever you do to the car.

?Is the 116/126 gauge too accurate for it's own good?

Bill

 

[Michel]

Michel, that's staggering - that temperature reading defies all logic
I do think that if your 6.9 does not reach proper operating temperature, you will use more fuel.
I'd be interested if you've ever done a fuel consumption test and what the result was or would be. Regards Styria

Godfather,

I was always of the belief that if I had to worry about my fuel consumption (on the 690SEL as well as any other of my cars) I should not own them as I would not be able to afford them

 

[SEL_69L]

6.9's have the same radiator frontal area as other 116's, and so the radiator has more work to do than with smaller engined 116's.

If your car is running hot, drive it conservatively on minimum throttle settings, and especially with a trailing throttle downhill. Asking the engine to do less work should help it to run a little cooler.

Perhaps some of our American Topklassers can share some of their experiences in running their W116's in hot conditions.

Many years ago, in Northern Queensland (Mount Morgan, 1968 to be exact), in mid summer, I was driving a Morris Major (remember those?), up a very long climb. Temperature must have been over 40 deg.C, and the engine began to overheat. I helped the engine by turning the in car heater on full blast. I cooked, but the engine did not: in fact the coolant temperature dropped slightly as I finished the climb. You don't need your engine to blow up when you are 3000 klm from home.

I another anedote, I was in an Austin Maxi ( remember THOSE? !) in 1970 on a climb to the top of Mount Grossglockner (perhaps Styria may be able to tell you where THIS mountain is located) and the car was running short of power, because of the very high altitude. The car was fitted with a manual choke, so I pulled the choke knob all the way out, and the car took off, as if I had just cut in the secretly installed afterburner. Incidentally, there was a very nice resturaunt on top of the mountain.

 

[Styria]

Godfather,

I was always of the belief that if I had to worry about my fuel consumption (on the 690SEL as well as any other of my cars) I should not own them as I would not be able to afford them

Hi Michel, it's not a question of how much fuel the car uses - fuel efficiency is the keyword here. No one should expect Fiat 500 Bambino consumption from a 2 ton 6.9. Regards Styria

 

[BenzBoy]

Hi Michel, it's not a question of how much fuel the car uses - fuel efficiency is the keyword here. No one should expect Fiat 500 Bambino consumption from a 2 ton 6.9. Regards Styria

Exactly - your point is achieving the optimum operating temperature as indicated by the best achievable fuel consumption - I have the opposite in the Spirit which has the 'outback pack modifications' and wants to run too cool all the time...
Regards,
Benz-Boy

 

[TJ 450]

I have heard that a lot of modern temperature gauges stay in the central position over a range of temperatures to ease concern of the driver.

My 450SEL was running at 85c most of the time and I have just changed the fan clutch in the 6.9 with great effect. You can hear the fan roaring now and the temp has not gone in excess of 85c with the engine running today. It will always creep up to 90c after a hot soak though.

80c seems a bit low, but a cooler thermostat may be beneficial in summer.

Tim

 

[s class]

My blue 6.9 has an 80 deg aftermarket thermostat and it runs pretty much on about 82, unless its really hot in traffic with the aircon on, in which case it can go just over 85.

My 280SE runs at about 80, but lately it is going above 90 more often that I would like in summer traffic. But then the fan clutch is stuffed, the radiator core is leaking, and the fan shroud is missing. Damn, the poor car, I really need to give it some TLC in the new year.

That Aus spec 450SE I'm working on required a new thermostat. The dealer supplied a 75 deg item, based on the VIN. I was surprised.

 

[Styria]

It's quite remarkable that the manufacturer of the two models, viz. the M117 - 450 and the M100 - 6.9 should specify different thermostats for the two engines. As I previously said, fitting the 87 degree thermostat to the 450 just simply did not work - it just simply ran so much hotter.

Also, there needs to be some suspicion concerning the quality of recores that I had made up for Gleaming Beauty and also ChrisP.'s Astral Silver Wilhelm. I had been patronizing the guy for years, but I only just found out about a month ago that he was ripping me off pricewise - and just to think that I trusted the guy.

I would also ask this question - the auxiliary fan. Mine cuts in at about 85 degrees because I replaced the original switch with the one hundred degree setting. B13, TJ 450, SEL69L, Michel, ChrisP., CraigS and any others, have you guys noticed at what stage this fan comes on, can you hear it, and also how noisy is it when you are actually listening when not sitting in the car. I would be greatly interested in your findings or experiences. Regards Styria

 

[TJ 450]

The aux. fans are quite noisy, you can usually hear it running from inside the car. Mine have never come on by themselves though, only when forced, as the temp has not exceeded 120 degrees C on either car.

The 450SEL has the 85 degree thermostat as supplied by Diesel Motors.

Tim

 

[WGB]

My 126 300SE had it's fan set to come in at 110 or when required by the aircon which was absurd and the switch was replaced with a 100 degree one which worked well.

The standard set up (as far as I know) uses the temp sensor on the head as one switch and the temp sensor on the Aircon line as another - either can turn on the fan.

Both my 450 and 6.9 have had the fan switch wired via a relay so that the fan runs whenever the air-conditioning compressor clutch cuts in.

This is standard practice as far as I know when the system is converted to H134a.

It is what most M-B's post 1990 do and all Jap cars and tends to make the temperature sensors a bit irrelevant but they can still be wired in as a backup.

Bill

 

[AAB]

I had an overheating problem on the 450SEL & replaced the core,..perfect.

I have owned this car for 20 years now & on inspecting the water reservoir during the fault elimination process, ( after replacing thermostat & fan clutch ) I noted that the recommend cold water level, (written in German on the side of the reservoir), is at the widest part of the reservoir, NOT the top, as I thought.

You learn something every day,

Season's greetings & regards,

Alex

 

[John S]

Mercedes allows room for the coolant in the system to expand.

 

[s class]

My 280SE has what I believe is the correct temperature switch for the aux fan. It sits on the side of the cylinder head, and is a so-cally 100/90 switch. It switches on the fan when the coolant reaches 100degC, and keeps it on until the coolant is down to 90degC. And its operation corresponds exactly with what I observe on the temperature guage.

Neither of my 6.9's has ever got hot enough to activate the aux fan.