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Discussion Starter #1
In the last few days, which have been really hot, I have been driving the SEC and noticing different temps. With it about 90f without the air, engine runs about 80 on highway and 85 in normal traffic. With the air on and in stop and go traffic, about 100. On the freeway about 95. This is with a new t stat, 80 degrees, new water pump, new radiator, new sensors, new fan clutch and water wetter. That is just so you know where I am coming from, But here is my offer. I think we all have seen lots of temp posts, but I have never seen data on what the cars run on some various days.. So if you think of it send me the following info when you think of it and I will set up a spreadsheet so we can kinda see what is “normal”. That way we can determine what we have to do. For me I would like to see 80c all the time. And yes the electric fans work too!

Try it this way

90 outside. Temp with and withou the air and type of driving. City or freeway

75 outside, same way

50 outside, same thing.

I suspect that the system was designed very close to being just enough. Also wonder if they put in a different radiator in hot climates.
 

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Both my 1989 SEC and 1989 SEL run at 80c all the time. Pretty much period, no matter the outside temp. I've driven both cars in freezing weather and in super hot weather. I have seen higher temps when climbing a long grade in the heat but not significant.

When I start the car after stopping at a store on a hot day, the gauge will be a little higher but moves right down once the engine is running. Both cars have used radiators and as far as I know, original water pumps.

The only time I saw scary temps was in Death Valley once when it was 119 degrees F. The car ran a little above 80c when we were moving but got right up to the top of the gauge when stopped and idling. Turns out the condenser fan was running backwards so while interesting, I don't have accurate data for that scenario.
 

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Mine are both 420's but for comparison, a smidge above 80c on the gauge no matter what. Both get up to temp very quickly when if it were -10c outside. Both stay the same temperature in traffic, with the exception of air conditioning on, stopped traffic, I've seen a smidge above about 90c on the gauge.

There's a huge motorway hill I like to tank up, both cars gauges indicate temperature rising quickly up there. It's about a mile up and full throttle, cos its fun. Otherwise it doesn't really move.

Maximum temperatures here in the last couple years have gone a bit crazy and we've not seen this as a routine temperature before, but not exceeding 32/33 centigrade. Same behaviour from the cars, no change in operating temperature.
 

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My 91 560 almost always has the air on and normally runs a smidge over 80C. With temps of 92F air on in traffic runs up to about 86-88C driving with AC over 90C never goes over 81-82C.
 

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Discussion Starter #5
Thanks all that does answer a question for a lot of us in that in all conditions, if everything is correct temps should hiver around 80 c even in hot days. I think from my reading on the forum over the years that does not hold true for many of us. Back to the drawing board. Last thing for me to check is the antifreeze/water mixture
 

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Yes it would seem there is an anomoly that causes an almost set level of temperature variance. I know Malcolm went through this too. Weird isn't it.

Doesn't help that the quality of thermostats can be so poor, more so lately, but at least they are easily tested.

For me I've only ever had them get hot in traffic, and then quite quickly. As in, pull up at some lights and it would go up to 100 in no time. One car managed itself with its electric fan, until I changed the radiator and then it was perfect and has been since.
The other, took this opportunity to show me the aux fan was not operational and went right up to scary horror levels. Stuck in London traffic so no escape. New radiator, freeing up the aux fan, discovering the trigger was faulty for that so installing a glovebox switch instead. And been perfect since then, no aux fan needed ever as it's so consistent.

But whats weird is that people on the forum can replace so many parts and the same result each time. Paging Malcolm....
 

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My brand new 80C replacement thermostat, when tested in the kitchen saucepan, revealed it was just starting to open at a measured 85C Plus degrees.

Here it is just slightly cracked open at a measured 197F degrees [91.77C].

No wonder my car was running 100C all the time warmed up! Yeeesh!

A 79C BEHR/MAHLE T/stat solved that issue once & for all.

On Thursday, with an observed ambient temp of 36.5C, I saw 82/85C on the temp gauge, stop & go parade traffic with the ACC on.
At 45 to 80mph on the same day, temp gauge read a mere whisker over 80C.

M
 

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Discussion Starter #8
Well tomorrow I put in the 75c one to see what happens. Will test it first just to make sure. I think now I can get stats removed and replaced in about 20 min. You should see me on valve adjustment pucks��. Thanks to all I would not go this far without all your info so thanks and I hope it helps others diagnose their issues. A baseline of what to shoot for is great. Again, bottom line for those that have temp issues, if everything is working you should only see a high of around 85C. I have new everything so it has to be the stat or mixture.
 

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I have new everything so it has to be the stat or mixture.
I have "new everything" too, including the pod on the left with the engine temperature, fuel gauge and oil pressure. The problem? The fuel gauge never reads 100% full and the temperature gauge now seems to read 10C too high. Engine temperature is very consistent whether in traffic in hot weather with the aircon on or at high speed during the winter. But always reading around 100C.

When I first noticed this, the reading was just above 100C. So I laser-measured the actual temperature by the sensor and that read 87.5C. I think the sensor is the original one; 1991 300CE-24.

Then I changed the temperature sensor for a cheap one made by Meyle. Still just above 100C.

And then a more expensive one from VDO. Now reads just under 100C.

I now have a genuine MB sensor and shall fit it at the weekend.

Where is the problem: sensor, gauge, laser thermometer?

Who knows. Not unduly worried.

RayH
 

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If both the fuel gauge and the temp gauge are off, and you recently changed the gauge cluster, I'd look at the cluster or the power to it. The gauges reference the source voltage, so if it's off so are the readings.
 

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Discussion Starter #12
I am going to go off the reservation a little here (seems I do quite often) but when I was researching what brand of radiator to get (Nissens, Behr) most of the comments came back Nissens. I think it was 60-40 or something like that. Most likely price but.... here is my question:

Has anybody ever researched out what the heat rejection value each brand gives off? Or for that matter, the MB one. So, if you are a radiator firm,you must figure out the heat rejection value of what you are designing or manufacturing. For instance, one would think they would say, well lets put in 200 degree water, at x flow, and with xx amount of air flowing across its coil, and the water is returning at xxx temperature then we are going to be rejecting yyy BTU’s of heat.

The reason this is important is that not only should price enter into the decision, but warranty, fit, and heat rejection.

I know if I knew one brand shed xxx BTU’s and the other xxx+ then it would matter.

Same thing kinda when you look at a three row unit or a four row unit. Is one better than another? Who knows without that info.

So if anyone knows the answer or has researched it, let us know. I probably will try to get something from the mfg’s but won’t hold my breath.
 

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It would be interesting to know.

When I first noticed my temperature rose at a stop on the SE, it was in anyway to the independent specialist so they did the radiator for me. Annoyingly I don't remember the name, only the mental price, which was heavily discounted for him but still not a cheap item.
I usually have MB only on this car but I can't be sure it was MB. Anyway it seeped a little at the seams. Not enough to worry about really, and fast forward probably 7 or 8 years, it was getting worse so I replaced it with a Nissens one. No difference at all in engine temps, identical behaviour.

I get a bit worried having read the problems that seem to occur for an unlucky few.
 

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Discussion Starter #14
Installed the 75 c short stat today and I filled it with water after the install. Have you ever noticed whatever job you do there is just one bolt or nut that is a pain? Well the tstat housing has one behind things. Damn thing. At any rate after install I let it idle in the drive way with the air on. Sure enough it rises to 100. I test the fan and yes it runs. Shut the air off and take it for a short run. Temp stays at 100 so I bring it home. I did fill the system with the upper hose off to see if I could make sure it was full. I will let it set tonight to see if it needs more coolant. If not will try a new stat.seems odd a 75 c stat is worse than an 80 one. Soon I will be boiling stats all over the place just to test them.

Thought you might lis to see the tail ends of the girls tucked in for the night
 

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I had the same problem with my 1990 SEC, my mechanic installed a new radiator and told me when he took the old one out it was 15lb heavier than the new radiator due to all the sludge that was left over the years. Since then my temp never goes over 80, in traffic or idling with A/C on full blast.
 

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Installed the 75 c short stat today and I filled it with water after the install. Have you ever noticed whatever job you do there is just one bolt or nut that is a pain? Well the tstat housing has one behind things. Damn thing. At any rate after install I let it idle in the drive way with the air on. Sure enough it rises to 100. I test the fan and yes it runs. Shut the air off and take it for a short run. Temp stays at 100 so I bring it home. I did fill the system with the upper hose off to see if I could make sure it was full. I will let it set tonight to see if it needs more coolant. If not will try a new stat.seems odd a 75 c stat is worse than an 80 one. Soon I will be boiling stats all over the place just to test them.
Totally Bizarre!

In that my 100 gauge immediately went sub 80C with a 75 installed, I thought you'd be outta the woods by now.. Daaaang.
 

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Sure the guage is 100% accurate? Maybe test engine/coolant temp using a laser thermometer as rayhennig mentioned above?
 

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Discussion Starter #18
I did test the top of the t stat housing and it matched the gauge. Today I put the 80c degree t stat back in and it lowered the temps more than the new 75 c one. I likely will order another 75 t stat and try a different model. Weird. Almostlike my valve puck issue, which I have not finalized that thread on.
 

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I had problems with my 560 SEC several years ago and like you I changed multiple parts trying to fix the problem.
1) buy real Mercedes parts and not the aftermarket want to be's especially the fan clutch ......... this ultimately corrected the problem for my car.
2) when changing radiators, there are units out there which physically fit into our cares, they are single row radiators and not adequate for our cars. NOTE when looking for these items they are listed as being the right part.

Before installing MB parts my temp was running as high as 100 and slightly higher at times and I would shut off the A/C to help get the temp lower. Now I do not have any problems I'm the hot Florida weather and the temp sits steady at 80 plus degrees with a/c on. and 80 with it off.

Hope this helps, Ken
Oh by the way I have an extra "good" radiator the I had installed for about 2 months when I was doing my trouble shooting, that I would like to sell if anyone is interested
 
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