motoman

Is it only MB who thinks coolant is good for 15 years? Keep looking at the manual which is silent on changes. Has anyone found the mysterious silicate packet in the expansion tank or radiator ?

Is coolant sometimes like sea water in the C63? Take a look at the pictures of corrosion members have furnished.

Anyone have a good pH meter and what does is read in your coolant? Anyone try a multimeter reading a la you tube, with one probe grounded and one in coolant, looking for less than ? .05 volts? A bogus method?

tfthach13

Coolant should be serviced every 3 years or so. MB is only saying 15 years because the EPA want fewer fluids being used. It's all politics. Find yourself a knowledgeable mechanic who knows their stuff and you'll be good.

I'm not sure about mileage, but I believe it's every 60k miles.

whoover

pH won't tell you anything and electrical conductivity even less. The chemistry of 15-year coolant is complicated.
http://w124performance.com/docs/mb/o...ze_article.pdf

Adding tap water to the coolant will likely screw up the corrosion inhibition of the coolant, as discussed in the article. But as long as you always top up with a 50-50 mixture of 325.0 approved coolant (like Zerex G-05) and DISTILLED water, the 15-year interval is real.

motoman

Whoover. A good article every MB owner should read, but...

The article is undated and silent on AMG vehicles. My owners manual implies the coolant is 15 year, but...

The article discusses cast iron but not high strength alloy steel and does not talk about replenishment of that (those ) additve (s).

Headbolts shown in the forum are corroded and breaking due to the corrosion IMO. The replacement headbolt appears to be beefier in the shoulder and head area, but IF corrosion is the culprit, more sacrificial steel will only buy more time. Have you seen any specifics on AMG ?

bhamg

Does the presence of air in the coolant enter into the equation IYO?

whoover

The article applies to our cars. It talks about aluminum cooling systems. It also mentions that the additives leach out very slowly and after 15 years most of the chemicals are still in the silica gel. The old bolts were too weak for the task. They don't rust through.

The C63 schedule is the 15 year one. It's not implied, it's stated. MB and especially AMG are so conservative, I see no reason to second-guess them.

If an owner really wants to flush the system sooner, it won't hurt as long as they use the 50-50 mix of 325.0 coolant and distilled or deionized water. Using another coolant because "I'm changing it so often I can use anything" is not a good idea.

But MB/AMG says it's a waste of money.

whoover

Unless your water pump is cavitating, which is a condition that indicates a mechanical problem, I don't understand what air has to do with it. If the overflow tank is filled to the right level and the water pump is ok, things are good.

bhamg

Sorry I wasn't clear...I was referring to corrosion.

motoman

Very strong evidence that corrosion is weakening the headbolts. Undercuts observed at the filets. Air bubbles percolating at an overheating head are rust drivers. (This perforates diesel cylinders.)

The galvanize coating of the headbolts is sacrificial and time related. Once depleted the steel goes. Also the zinc stops protecting around 250F. Where is the coolant temp sensor located that reads out to our dash instrument? Anyone?

whoover

The head sheared off in many cases. It's not like coolant was circulating around a torqued head bolt. If the bolt hadn't failed there would be no contact with coolant at all. The "undercutting" is more likely stretching due to steel that can't take the strain. There are plenty of pictures of failed head bolts and rust doesn't seem to be an issue in the ones I see. Mercedes changed the bolts, not the coolant schedule.

Again, I don't get what coolant refresh has to do with bubbles. If your water pump is cavitating, it's not a coolant problem. If you have a leak and got air in the system, it's not because the coolant is old. If you have a leak and topped up with water at a gas station, well then yes you have to flush the system and restore the proper coolant mix. And fix the leak.

motoman

"...the head sheared off in many cases..." ?? Please tell us more.

M 156 "wet deck" design uses coolant around the head bolts.

..."rust is not an issue'' ?? Search pictures in forum.

Cavitation is not the issue here. Removed headbolts show corrosion undercutting like a saw cut. They are not protected at that stage.

bhamg

It's my understanding that localized hot spots around the combustion chamber can cause a layer of water vapor to form from boiling. This vapor serves as an insulating layer which prevents heat transfer, which in turn exacerbates the condition. So, logically you need a way to reduce surface tension to dissipate vapor bubbles if this is happening so coolant can conduct heat away from the area, otherwise nothing changes. Hence, my query about the corrosion we are seeing in MANY head bolts and its possible cause(s).

whoover

I'm only pointing out that those conditions have nothing to do with "old" versus "new" coolant. Again, assuming that the proper coolant is used, with the proper mix (50-55% coolant in distilled water), it's something that the engineers either dealt with or didn't.

And @Motorman,

Here is a picture of a sheared bolt:
http://mrtazzy.com/?page_id=59

MB changed the design to avoid taking "meat" from the top part of the bolt:
http://farm8.staticflickr.com/7071/7...deeb1cfe_b.jpg

All indications are that the problem was bad bolt design, has been corrected, and has nothing to do with corrosion.

Ingenieur

I don't think corrosion is the cause of failure

The reduction of cross area is inconsequential and the corrosion is most likely a consequence of failure, not the root cause
And starts before it snaps during the elastic stretching leading up to failure

It was simply the wrong bolt type for the application: internal torx vs external

For a static joint with only internal stress like a structural member fine

For a system with external cyclic forces (bear in mind the force driving the piston is also on the head) it is not a good choice

The head flexes/collapses inward on itself and stretched the shank at the bolt head

motoman

The several bolts had severe corrosion pitting which ate away the filet radius under the headbolt head. On the failed unit only a fraction of any filet was left on the shoulder and corrosion craters daisy chained around the fracture line on the remaining circumference. On the intact headbolt corrosion had already undercut the filet and edge of the bolt head.Easy bending once the undercut is establshed. LIke a nail with dike marks. More center material to resist with the new OEM headbolt. What about edges?