Aluminum/Iron engines, coolants and head gaskets

[JHZR2]

As many know, Ive got a 91 MB 350SD undergoing HG replacement, this is an iron block, aluminum head Diesel engine.

This family of engines, the OM603 series, was a big step above the older cast iron engines, which are generally bulletproof but low tech and older designs. But when the 603 came out, early ones had head cracking issues, later ones (like mine), which went from 3.0 to 3.5L, had resolved head issues but had HG and in some cases, rod bending issues (often attributed to HG issues).

So, why the curiosity?

Al and cast iron have different coefficients of thermal expansion. I'd assume that designs of the dissimilar blocks and heads would result in a design that intends to keep as consistent set of temperatures at the interface, and allow expansion to preferentially occur in other dimensions to avoid sealing concerns. Is this correct?

Given head and head gasket issues, the family of engine in my 91 kind of needs whatever help it can get. My 3.5L is especially a challenge in this, as it was merely an OE bore out of the 3.0L engine, so gasket and fire ring materials I would have to assume are reduced. Then the chance for failure and seepage can occur.

Galvanically, cast iron and aluminum aren't that far off. But do fire ring materials come into play? Combine aluminum, cast iron and a third metal (fire ring) in there with an electrolyte, and you could have an issue. Add to that the cte mismatch, and who knows what can happen. I'd sssume some level of shearing under thermal changes, a possibility for coolant to seep around under such cases, and then what...

Now, coolants... G-05, the old Mercedes standard, is designed for considering HD and cast iron applications..

Then they back-spec G-48, which is compatible, but offers 2-eha. Now G-40 (is in use, not sure about back-spec)which is different again, and not clear if it is good for cast iron, mixed metals, etc.

So, how,does this all play in? What's the best selection of coolant for an aluminum/iron system, given that we know that there are potentials for challenges with the materials and design of the engine? Would G-40 offer some superior protection these days? Is G-05 the only right selection for older Diesel engines? Does g-48:factor in somehow given the mixed engine materials?

Any other thoughts as to what might be at fault or ideal to protect an aluminum/iron engine would be great. Also any thought she on how coooant affects HG life in this mixed meta scenario would be appreciated.

I'm posting in general topics versus coolants because this is a much more holistic question. Does anyone have any thoughts for best protection of aluminum/iron engines in light of the newest technologies. When done with the HG job I do t want to do it again...

Thanks!

 

[MCompact]

I've owned several cars with aluminum heads and iron blocks past 150k miles and I've always just used the coolant sold by the car's manufacturer.

 

[CharBaby]

I've had alum heads w/iron blocks that blew HG all day long. However, these engines were know for doing so(Chrys. 4cyl 2.2/2.5, GM 2.8/3.1 V6). And I've had alum heads w/iron blocks that never blew a HG in 300K miles(Honda). So, it depends on the mfg.

 

[Shannow]

Mixed metal plays havok with gaskets, with Al expanding longitudinally twice that of the iron.

So in theory, an alloy headed 6 should work the gasket more and have more problems than (say) a V-6 - which then also has twice as many gaskets to fail.

I've seen engines go forever, and significantly shorter.

Neglected cooling systems seem to be a significant issue (which I'm sure you don't), and as others have said, some designs.

 

[dlundblad]

Look into Zerex Asian since it contains no 2-EHA. Long life and somewhat like a HOAT, but plays well with aluminum.

The only thing that stinks is it's only available in 50/50 as far as I can tell and around $15 a gallon. In my uneducated opinion, Kubota concentrate is close in chemistry and in price at ~$28 per gallon. Obviously good for diesels and HD use. Perhaps either a Honda or Toyota OE coolant would be close too, but I'm not sure.

 

[Silk]

Originally Posted by Shannow

So in theory, an alloy headed 6 should work the gasket more and have more problems than (say) a V-6 - which then also has twice as many gaskets to fail..


Falcon and Commodore eh ? Although the Commodore V6 was all cast iron....but the Falcon was a headgasket blower and head twister all day long. That's why I preferred the old original non Xflow Falcon engine. First alloy head on cast iron we came across was the Hillman Hunter, it blew no more gaskets than a BMC or Holden, but problems were because we didn't use an inhibitor.

 

[Shannow]

Silk,
not specifically for those but more a reference for why the 4s did better than most of the sixes....

 

[JHZR2]

Originally Posted by dlundblad
Look into Zerex Asian since it contains no 2-EHA. Long life and somewhat like a HOAT, but plays well with aluminum.

The only thing that stinks is it's only available in 50/50 as far as I can tell and around $15 a gallon. In my uneducated opinion, Kubota concentrate is close in chemistry and in price at ~$28 per gallon. Obviously good for diesels and HD use. Perhaps either a Honda or Toyota OE coolant would be close too, but I'm not sure.


G-05 which was long on the MB list, has no 2-eha either. Is there a reason to think that G-05:doesn't play well with aluminum?

FWIW, despite the HG challenge, the car was well maintained and had G-48 in it.. but if 2-eha is a concern for HGs, then it's a consideration as I'd like to try to optimize longevity.

Seems like it may just be hit or miss...

Hit or miss is what I've observed with these engines - especially the 3.5. You either have failed ones around 100k (given that I observed the oilmto coolant issue it seems that HG issues can be a contributor), or ones that are at 270-300k...

 

[JHZR2]

Originally Posted by Shannow
Mixed metal plays havok with gaskets, with Al expanding longitudinally twice that of the iron.

So in theory, an alloy headed 6 should work the gasket more and have more problems than (say) a V-6 - which then also has twice as many gaskets to fail.

I've seen engines go forever, and significantly shorter.

Neglected cooling systems seem to be a significant issue (which I'm sure you don't), and as others have said, some designs.


So I know upfront that this design took some liberties, to say the least. And you hit the point exactly - Al is going to expand quite a bit more, shearing or otherwise affecting the HG somehow...

The 3.5L "rod bending" set of theories is an interesting set of discussions to read.

Essentially lots of folks started to observe high oil consumption, then found out of round bores, especially in cylinder 1, due to bent rods. Of course this is a bored out 3.0L, so there's less material, less gasket, etc.

One main theory is that the HG gets breached, starts to allow liquid into cylinder 1, which then causes a "mini hydro lock" which in time causes the rod to bend, causing an oblong stroke, causing an ovoid bore and consumption, which around 1qt/400 miles starts to affect drivability.

You're right, Ill maintain the cooling system - over maintain it perhaps. Im not sure if I should be concerned with the 2-eha in G-48, or if since I'm at a clean slate, perhaps should even consider g-40 in there...

Just want to do whats best for longevity, both from a cooling system and HG position, given that there will be a nagging concern...

Thanks!

 

[eljefino]

I've always thought gentle warm-ups were the best thing for aluminum-on-iron. Stuff's going to expand, and the gasket's going to rub. I just want it to be gentle.

If your thermostat doesn't have a hole or jiggle pin, I'd put a tiny one in. Having it going from water tight to slammed open will add thermal stress to the pocket behind it.

Did 91s originally come with traditional green or was G05 a thing already? You're trying to guess what a service replacement head gasket is optimized for, coolant wise.

I remember BITOG of yore where G05 was the bee's knees. Advance didn't even sell it; had to pay NAPA $19/gal for my [censored] dodge neon. Guess I'm not with the times. On a project like this, it's probably what I'd go with, though, due to the age of the car and my perceived greater local availability vice G-48.

 

[Trav]

The other issue with a diesel is cavitation. I use JD Coolguard II it is made for mixed metal engines gas and diesels and you can use JD test strips to test it, you cant go wrong with this coolant.
Mixed metal engines use a MLS (Multi Layer Shim) head gasket that is coated usually with Teflon so it can move with the different expansion rates of the metals as you pointed out. The movement is minuscule but along with the coating is absolutely necessary to prevent gasket tearing and damage.

 

[caprice_2nv]

Originally Posted by Char Baby
I've had alum heads w/iron blocks that blew HG all day long. However, these engines were know for doing so(Chrys. 4cyl 2.2/2.5, GM 2.8/3.1 V6). And I've had alum heads w/iron blocks that never blew a HG in 300K miles(Honda). So, it depends on the mfg.


As far as Honda goes, they are known to eat head gasket's too. I don't know specifically what years but my friend's girlfriend has an early 2000s Civic and he had to replace the head gasket shortly after he bought it for her. It only had about 120k miles at the time. I've heard of others doing the same. Some go forever no issues and others don't. I believe the gm 2.8/3.1 and 3400 are in the same boat. My mom's 99 Alero needed intake gasket's (under warranty) but it went over 200k no issues with head gasket's.

Different engine models are more or less prone to gasket failure but even then it just seems to be the luck of the draw sometimes. That said it can't hurt to know what coolants may help with the potential problem long term.

My own 1976 350 Oldsmobile was all cast iron but I replaced the intake manifold with an aluminum Edelbrock before I swapped it into my car. The gasket lasted about 10-11 years and nearly 100k miles before it failed and leaked profusely. The head gaskets are still original despite forgetting to turn on my electric fans and having the engine get over 260 degrees once about 8 years ago. I use regular old green coolant changed every 3-4 years. I always expected the intake gasket to fail but I didn't expect the junkyard engine to be running fine 12 years and 100k later. Soon I'll be having to replace the water pump again I'm sure.

 

[supton]

Originally Posted by JHZR2
As many know, Ive got a 91 MB 350SD undergoing HG replacement, this is an iron block, aluminum head Diesel engine.

I've got nothing to add but I'm looking forward to the thread at the end of this repair.

 

[MrMoody]

Originally Posted by Char Baby
I've had alum heads w/iron blocks that blew HG all day long. However, these engines were know for doing so(Chrys. 4cyl 2.2/2.5, GM 2.8/3.1 V6). And I've had alum heads w/iron blocks that never blew a HG in 300K miles(Honda). So, it depends on the mfg.

We had an 85 Omni 2.2 NA and an 89 LeBaron 2.2 turbo, both ran a huge number of miles and neither ever blew a head gasket. The Omni's suspension wore out and the wife didn't want to put any money in it, and the LeBaron after over 300k had so much blow-by you couldn't keep seals in it. My stepfather also had an 88 2.2 turbo Daytona, and a friend's daughter had an 87 2.5 turbo LeBaron that never did it either, that's just off the top off my head. I never knew one that did it, so it couldn't have been all that common. Those engines were far superior to the Mitsubishi and VW ones they used earlier. My cousin had an (84?) Dodge 600 with the Mitsu 2.6, and it DID blow the head gasket. We also had a 94 3.1 Corsica that ran over 200k until my daughter wrecked it, and that car even got overheated once with a leaking radiator. The head gaskets held on it, too.

 

[CharBaby]

Originally Posted by caprice_2nv
Originally Posted by Char Baby
I've had alum heads w/iron blocks that blew HG all day long. However, these engines were know for doing so(Chrys. 4cyl 2.2/2.5, GM 2.8/3.1 V6). And I've had alum heads w/iron blocks that never blew a HG in 300K miles(Honda). So, it depends on the mfg.


As far as Honda goes, they are known to eat head gasket's too. I don't know specifically what years but my friend's girlfriend has an early 2000s Civic and he had to replace the head gasket shortly after he bought it for her. It only had about 120k miles at the time. I've heard of others doing the same. Some go forever no issues and others don't. I believe the gm 2.8/3.1 and 3400 are in the same boat. My mom's 99 Alero needed intake gasket's (under warranty) but it went over 200k no issues with head gasket's.


Oh Right,I agree, can't deny that!

And not every Chrysler or GM known HG eating engine had the problem. I too have known others with said engines and never had a HG replaced in over 200K miles. The thing is, there were way too many problems that went unaddressed for way too many years.

And I too have heard(didn't know anyone) of some year Civic's having these HG issues. But, on a much smaller scale for fewer years before it got addressed by Honda.

However, there is a difference between MFGs having HG issues in certain years and other MFGs being notorious for having these problems for way too many years.

Just a thought,

CB

 

[atikovi]

Originally Posted by JHZR2
As many know, Ive got a 91 MB 350SD undergoing HG replacement, this is an iron block, aluminum head Diesel engine.


You might post this on some Mercedes forums like http://www.peachparts.com/shopforum/diesel-discussion/

 

[JHZR2]

^ thanks. I am on there.


To be clear to all, my HG never blew. I observed a slight amount of oil in the coolant overflow and knew it was time. UOA didn't indicate that there was coolant or water in oil.

But the time was right, IMO.

 

[JHZR2]

Originally Posted by eljefino
I've always thought gentle warm-ups were the best thing for aluminum-on-iron. Stuff's going to expand, and the gasket's going to rub. I just want it to be gentle.

If your thermostat doesn't have a hole or jiggle pin, I'd put a tiny one in. Having it going from water tight to slammed open will add thermal stress to the pocket behind it.

Did 91s originally come with traditional green or was G05 a thing already? You're trying to guess what a service replacement head gasket is optimized for, coolant wise.

I remember BITOG of yore where G05 was the bee's knees. Advance didn't even sell it; had to pay NAPA $19/gal for my [censored] dodge neon. Guess I'm not with the times. On a project like this, it's probably what I'd go with, though, due to the age of the car and my perceived greater local availability vice G-48.


G-05 was specified at least as far back as 1976 AFAIK.

It is good stuff, designed for diesels and mixed metals. It has been great for keeping original cooling systems in my w123 cars...

$13/gal for concentrate at NAPA.

 

[fdcg27]

What about an email to Germany?
Tell them what you have, what you're doing to it and ask what coolant is preferred for long HG life as well as corrosion protection for the different metals.
No other maker seems to take as much pride in supporting its older cars still in use, and not just the high luxe models either.
I suspect that whatever email address you can find your question will get forwarded to someone who can provide a good answer.

 

[clinebarger]

Originally Posted by Char Baby
I've had alum heads w/iron blocks that blew HG all day long. However, these engines were know for doing so(Chrys. 4cyl 2.2/2.5, GM 2.8/3.1 V6). And I've had alum heads w/iron blocks that never blew a HG in 300K miles(Honda). So, it depends on the mfg.


I can't think of a Honda engine with an Iron Block?