6.9 too hot?

[diametricalbenz]

I was driving the 6.9 and sitting in Burbank, CA traffic and the ambient air temperature was 90F or so and I saw the temp needle rise just below the white mark before it goes into the red at 250 F. I turned on the heater to no avail. The PO replaced the water pump a few years ago. The coolant reservoir is full and the overheat fan is functional.

Should the car be running this hot even in these conditions or is something not functioning properly?

[oxymoron]

As many times as I have read in the manuals that it is okay to nudge the red or even go into it briefly, it's not a very good feeling to watch the temp gauge when it does that.

I have seen my car do that a couple of times and it has never failed to recover to a normal temp when I was able to get up to speed again, but only when everything was working right. If your car won't recover a cooler temperature when you resume a highway speed, then something is probably wrong.

My 6.9 is suceptible to needing to be burped any time I do anything with the cooling system. It should purge the bubbles to the highest part of the system in the overflow tank, but mine doesn't always do it. I got a new servo a couple of months ago and got a swinging temp needle until I bled the bubbles finally. Same thing with Aux Air Valve. replaced and had to burp it a few times until all the bubbles were gone.

I just put in a new thermostat a few weeks ago and yesterday replaced my overflow tank. Tank had a hairline crack that was causing it to lose pressure.

Also got a new tank cap. It's been mid-90s in Houston for awhile now and I have gotten used to replacing cooling related stuff every couple of years as a preventive. I broke down outside of Willcox AZ on a day when it hit 115 deg in 2000 when driving home and decided I wasn't going to let any $20 parts do that to me again.

The manauls say you can get that high as long as it doesn't stay there, but it seems too hot for me. Another thing I learned was that Mercedes temp gauges are more linear and accurate than most other cars'.

I'd look around the firewall for all the heater hoses in servoland. A small leak there can give you symptoms.

Right now it's mid-90s and same humidity and I drove home at lunch on the freeway at 85 or so and then got into stop and go traffic. It warmed to about 80 C on the highway and went to around 85+ in the stop and go.

I've got my Aux fan wired into the cabin and I can switch it on when I am in really bad traffic.

I think the recovery to a normal temp is key. If you get hot and stay there, there's probably something that needs fixing.

[diametricalbenz]

oxymoron,

Thanks for sharing your experiences and it sounds about the same with me. If I drive the car in 65F weather, the temp needle sits right in the middle of the needle range above the 175 and the white line above that (185F?). Although, when I drove it on the freeway in the "cold" 55F or so drenching SoCal rains a few months ago there were patches of uphill traffic and the temperature stayed constant at the 185F mark.

When it gets warm out and goes into traffic it starts to heat up and as mentioned, the indicator needle moves to an uncomfortably high temperature. The car seems to act like a cold blooded organism

I have to check my records to see when the thermostat was last replaced. Is that a pain to replace? I was looking in fastlane for a replacement and there are three models with no reference guide. 71F 79F and 87F Which one is supposed to be used??

I'll give the hoses a look again when I take it out for a spin but I haven't seen any prior leaking.

On a side note....I went to Occidental College here on the west coast and students and alumni alike are referred to as "oxymorons"

[boneheaddoctor]

This is not 6.9 specific but the principles remain the same....

These cars are old enough that you may have solder bloom on the radiator..or rust and scale buildup in the block....

Something a citric acid flush will improve greatly....My W116 300SD used to be prone to climbing temp guage everytime I came to a long hill in the mountains, since then I have done a very thourogh citirc acid flush the guage barely moves on the same hills much less climb to the red...

this may have a simple fix...don't ignore the obvious or cheap cures..

[300SDog]

how 'bout "Evans Waterless Coolant" ?

.... it's supposed to be the ultimate ass-kicker for lowering temps operating without water at verry low pressure.....

http://www.evanscooling.com/main25.htm

[oxymoron]

BHD: What's "solder bloom"? What does it do? I can see little BB looking things at the top of my radiator where the top attaches. It looks like solder has melted and re-solidified.

Diametrical: I just put in a 79 Deg. thermostat to replace the 87. I like it better. It seems to allow my car to recover a mid-gauge temp quicker. With the 87, temp would stay high longer before returning to center of gauge.

I know I don't want the car to run too cool, but since my breakdown in the desert, I always keep an eye on the temp and a rising needle freaks me smooth out. I live in a freaking swamp.

[boneheaddoctor]

Originally Posted by oxymoron

BHD: What's "solder bloom"? What does it do? I can see little BB looking things at the top of my radiator where the top attaches. It looks like solder has melted and re-solidified.

Diametrical: I just put in a 79 Deg. thermostat to replace the 87. I like it better. It seems to allow my car to recover a mid-gauge temp quicker. With the 87, temp would stay high longer before returning to center of gauge.

I know I don't want the car to run too cool, but since my breakdown in the desert, I always keep an eye on the temp and a rising needle freaks me smooth out. I live in a freaking swamp.

If you take a flashlight and look inside at the upper part of the core (through where the upper hose attaches) if you see a fluffy white stuff around the tubes you have solder bloom....solder will corrode and it looks like that when it does...it will block the tubes dramaticly reducing radiator efficiency....this will be limited to soldered brass radiators...alluminum ones will have other issues, just not this one.

It takes a long time for it to occur....but these cars are old enough for it to be an issue...it plugs up heater cores also......

[oxymoron]

Oh yeah. Thermostat is easy to replace. A few allen bolts on top of the housing at the top radiator hose. Make sure the little vent hole in the stat is pointing toward the engine (at a higher spot than the radiator side of the thermostat when placed in the housing). You'll see this when you open it up.

If you open it up, even cool, you'll probably lose some coolant and introduce a bubble. After you put the housing back on, if you want to burp it quickly and be done with it rather than wait for the bubble to circulate before it is returned to the overflow tank, top the coolant to the seam on the tank and let the car come to full operating temp. With the thermostat fully open and the cap off the tank, rev to about 2500 for a few minutes. I do mine with the front right wheel parked on the curb.

On my car, when I don't do this, the bubble rides around the engine for a couple of days and when it hits the temp sensor, the needle jumps.

[oxymoron]

And citric acid removes the corrosion?

[boneheaddoctor]

Originally Posted by oxymoron

And citric acid removes the corrosion?

There is a Mercedes procedure for this....


flush out the old coolant well...then use a degreasing agent....I use an off the self radiator cleaner.....run that as per directions...flush well with clean water ....

your avarage Benze will take 2.2 lbs of dry citric acid misd with water....run that for about an hour and flush repeatedly......you do want it all out....I run a pound of baking soda in the third flush after that.. to neutralize any remaining acid...continue flushing a few more times before putting in the correct coolant...

Make sure the heater is turned on full blast during ALL of this to clean out the heater core also...


You can buy the Citric acid at the Mercedes dealer or on Ebay....food grade or lab grade are both fine...adn far cheaper than the dealer....it will disolve rust and scale and solder bloom.....

Take your time its not a 2 hour job...more like 2 days....but the results will be well worth the effort. After 25 years or more there WILL be scale and rust no matter how well it has been maintained....any neglect in its life and that amount dramaticly increaces.

I would buy a bulk container on Ebay and do it twice....if it was really nasty inside.

Remember it take 2.2 lbs per time.....the containers at the dealer are far smaller and you need several. Ebay will be 1/4 the price for twice as much of the very same thing. Its used making soap and food....so just do a search on Citric Acid....

[oxymoron]

I have been wanting to do the citric acid flush. The flushing and refilling and the whole deal is done with the thermostat OUT, right? I may need a 3 day weekend for this. Mine's a daily driver.

Makes sense that it can be had cheaper than dealer. I will look at eBay. Thanks.

Something else I have done is to use the same principal as Water Wetter, but cheaper. It's Jet Dry, the liquid stuff used in dishwashers to prevent water spots.

It works the same way as 'wetter by breaking down the surface tension of water so that the water stays next to the metal and doesn't form bubbles on the metal which leads to hot spots.

[boneheaddoctor]

Originally Posted by oxymoron

I have been wanting to do the citric acid flush. The flushing and refilling and the whole deal is done with the thermostat OUT, right? I may need a 3 day weekend for this. Mine's a daily driver.

Makes sense that it can be had cheaper than dealer. I will look at eBay. Thanks.

Something else I have done is to use the same principal as Water Wetter, but cheaper. It's Jet Dry, the liquid stuff used in dishwashers to prevent water spots.

It works the same way as 'wetter by breaking down the surface tension of water so that the water stays next to the metal and doesn't form bubbles on the metal which leads to hot spots.

You won't be forcing the water through the radiator with no thermostat in it.....when the thermostate opens on the mercedes it forces it through the radiator What takes the time is getting it up to temp..letting it coll down drain and flush....run it up to temp...etc......if your engine has a block drain using that during the drain will speed it up. The OM617 has one on the right side just behind the motor mount. They others you will have to find on your own.

I was convinced I needed to have the radiator recored or something before I did mine....It Can work what seems like miricles in certain cases...

[diametricalbenz]

So it sounds like this would take a whole weekend to do. My situation is more challenging because I don't have a house or a realistically suitable place to perform the work. I have to do this on the street without a water supply and or one that isn't laden with minerals for filling and flushing and or a easy way to catch all of the coolant when flushing. Gonna need lots of bottled water.

So the steps are:

(leaving heater on)
1. drain coolant
2. use a radiator cleaner and follow instructions - flush thoroughly
3. 2.2 lbs of citric acid mixed with enough water to fill the cooling system, then drive the car for an hour? then flush...what's the procedure for flushing?
4. 1 lb baking soda - how long should it be driven before purging? then flush completely to remove any residue
5. fill with new coolant

[boneheaddoctor]

Originally Posted by diametricalbenz

So it sounds like this would take a whole weekend to do. My situation is more challenging because I don't have a house or a realistically suitable place to perform the work. I have to do this on the street without a water supply and or one that isn't laden with minerals for filling and flushing and or a easy way to catch all of the coolant when flushing. Gonna need lots of bottled water.

So the steps are:

(leaving heater on)
1. drain coolant
2. use a radiator cleaner and follow instructions - flush thoroughly
3. 2.2 lbs of citric acid mixed with enough water to fill the cooling system, then drive the car for an hour? then flush...what's the procedure for flushing?
4. 1 lb baking soda - how long should it be driven before purging? then flush completely to remove any residue
5. fill with new coolant

I would add a clear water flush between step 1 and 2
and I would do at least 2 clear water flushes before doing step 4
I would do the baking soda flush long enough to get the motor to operating temp then flush to be certain its fully circulated in the systen to neutralize any acid.....a couple flushes to be certain its gone....then fill with coolant and water thats not overloaded with minerals...to the proper mix.
the flushes regular old tap water is fine....

And yes with the heater on full blast the entire time so that part of the system is cleaned and flushed also.

Expect a lot of crud to come out after the Citric acid stage....

[oxymoron]

[QUOTE=boneheaddoctor]You won't be forcing the water through the radiator with no thermostat in it.....when the thermostate opens on the mercedes it forces it through the radiator What takes the time is getting it up to temp..letting it coll down drain and flush....run it up to temp...etc......if your engine has a block drain using that during the drain will speed it up. The OM617 has one on the right side just behind the motor mount. They others you will have to find on your own.


Yeah that makes sense. I guess I was recalling somebody writing about removing the thermostat. Maybe to reverse the water direction during a flush, but I understand what you're saying about leaving it in.

I want to do this in the summer, but the thought of having the heater on is not too good right now. My aux water pump is in questionable repair so leaving the car running with the heater on in the driveway may not be very effective.

I did a couple of fresh water flushes with no acid before the weather got hot and I was surprised at all the crap that ran out of there. The PO had run stop leak through it (and killed the servo right after I got the car) and that was 10 years ago so I know there's more stuff to be removed.