High silicate coolant for aluminum protection?

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This is from a GM EMD Locomotive Maintenance Instruction dated 1991:

SILICATE DROPOUT
With the increased use of aluminum in automobile engines, many of the antifreeze coolant manufacturers have
introduced high silicate antifreeze formulations. The primary purpose of the new formulations is to prevent
corrosion of the aluminum heat rejection surfaces as well as other aluminum parts.


Also, I found this from GM TSB 83-I-26 dated 01/17/1983:

Chevrolet Motor Division has in past model years recommended use of ethylene glycol base anti-freeze that meets GM Specification 1899-M. This recommendation has changed for 1982 and 1983 vehicles which are factory filled with coolant which meets GM 1825-M specifications. It is required that any additions of coolant to these vehicles be done with GM 1825-M. This change was necessary due to the use of aluminum components on some engines which required a different formulation of anti-freeze to prevent corrosion. This anti-freeze is available from WDDGM in gallons and drums as P/N 1052753 and P/N 1052754.

So it seems that there were once high-silicate formulations that were designed to protect aluminum engines. The only reference I've found to silicate levels found in these coolants is a patent from 1985, which suggested that levels of 1400ppm in undiluted coolant were typical (resulting in 700ppm in a 50/50 mix).

Responsive to such increasing use of aluminum, manufacturers of coolants for internal combustion engines have generally increased the silicate content therein. Silicate levels in many commercial coolants have increased about three- to eight-fold in the past several years. A typical undiluted coolant contains about 1400 ppm silicate as SiO2.


Given that any IAT silicated coolant you buy these days will have a max silicate limit of 250ppm because it meets ASTM D4985, has the need for additional silicates for aluminum corrosion protection been determined to not be required?
 
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I can testify that you didn’t want high Si coolant in a diesel, my F-450’s 7.3 IDI’s radiator bottom tank was FULL of silicate when I bought it. IMHO the Asian manufacturers (& GM, Benz, etc.) discovered that OAT and other more modern formulations protected better, for much longer, than silicate inhibitors.
 

brianl703

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I can testify that you didn’t want high Si coolant in a diesel, my F-450’s 7.3 IDI’s radiator bottom tank was FULL of silicate when I bought it. IMHO the Asian manufacturers (& GM, Benz, etc.) discovered that OAT and other more modern formulations protected better, for much longer, than silicate inhibitors.

The ASTM D4985 specification is for heavy-duty engines and does have a 250ppm Si limit.
 

JHZR2

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I think I’d argue that there’s enough history of substantial life from both iron/iron engines with Al radiators, and iron/Al engines with Al radiators, running on G-05 in Mercedes diesels from the 80s and early 90s, to say it’s proven when properly engineered.

Too much Si is a band aid that leads to sludged up mess.
 

brianl703

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But G-05 contains OATs which are known to protect aluminum.

What about the low-silicate conventional green? What is different about today's low-silicate conventional green that allows it to protect aluminum when low-silicate formulations in the 80s could not?
 
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I thought the new SIOAT antifreeze formulations were high silicate?

I also thought most HOAT formulations contained at least some silicates?

Some of the original OAT formulations used silicates.

The issue of course is they precipitate out over time forming the sludge no one wants.
 

brianl703

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They could be high-silicate, but as noted above, any coolant meeting ASTM D4985 (for heavy-duty diesel engines) is limited to 250ppm. G05 meets ASTM D4985, and so does every conventional green formulation I've looked at.
 
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But G-05 contains OATs which are known to protect aluminum.

What about the low-silicate conventional green? What is different about today's low-silicate conventional green that allows it to protect aluminum when low-silicate formulations in the 80s could not?
PHOAT's - primarily spec'd for Asian cars, contain phosphates instead of silicates.

I believe the reason the German OEM's dislike Phosphates is because the water in Europe has a very high mineral content, and when mixed with phosphates they can produce minerals that settle out and cause corrosion. This is why its especially important to use only distilled water with PHOAT's - so this doesn't happen. Most of the OEM packaged PHOAT's come already mixed to ensure this is not an issue.
 

brianl703

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PHOAT's - primarily spec'd for Asian cars, contain phosphates instead of silicates.

That may be the difference. Today's conventional green coolant contains phosphates AND silicates. Perhaps the phosphate level has increased to make up for the lower levels of silicates?
 
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Everyone had their own mix and could have included SIlicates and Phosphates. Perhaps your right in that they now use phosphates more - which are one of the active ingredients in PHOATS. Or maybe they found better ways to keep stuff in suspension. Or maybe there relying on demanding people use distilled water if there not buying premix?

I don't think for Automotive purposes the newer formulations say they can be run longer do they? Your still at the same change interval as the original.

Is there anyone other than PEAK that still makes and markets an IAT for automotive?
 
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Interesting about the locomotive instructions. I've only ever seen them filled with water from a hose and sometimes a dye added to check for leaks. I know antifreeze wasn't being used because if they weren't left running in cold temperature the freeze plugs would pop to drain the system before it could freeze and damage things.

Almost all I've seen ran only water and most I've been around are EMDs.
 
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Interesting about the locomotive instructions. I've only ever seen them filled with water from a hose and sometimes a dye added to check for leaks. I know antifreeze wasn't being used because if they weren't left running in cold temperature the freeze plugs would pop to drain the system before it could freeze and damage things.

Almost all I've seen ran only water and most I've been around are EMDs.
I don’t think most of them around here get shut down long enough to freeze. An engineer told me they have an auto start feature when they’re parked in a siding and if air pressure drops to a certain point they start up to rebuild pressure. I don’t know if that’s true but I do recall seeing one parked on a side track near the house running with nobody around.
 
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I don’t think most of them around here get shut down long enough to freeze. An engineer told me they have an auto start feature when they’re parked in a siding and if air pressure drops to a certain point they start up to rebuild pressure. I don’t know if that’s true but I do recall seeing one parked on a side track near the house running with nobody around.
If they have been retrofitted (or are new) yes - https://www.ztr.com/solutions/intelligent-starting-technology
 
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FWIW, a copy of this was in with the paperwork I received when I get the Legend. While I don't use Honda branded coolant, I do use a non-silicate coolant.
honda coolant.jpg
 

FCD

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Silicate is still the best inhibitor for aluminium, it acts quickly and is very effective, the Silicate passivated the aluminium, it partially "absorbs" the Silicate, the bad part is that the Silicate depletes relatively quickly and can gel, although the problems with gelling have been more or less figured out now.

I am using G11/G48 in both my cars and have been for about 3 years now, no issues whatsoever with gelling or anything else for that matter, and that's with a Silicate level of about 700ppm, probably the most out of any modern coolant, at least that i know of.
 
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The danger of high silicate, especially in diesel applications, is that it bonds with cast iron (or aluminum) engine parts & vibration flakes the silica off & it accumulates in the cooling system. Combining with minerals from hard water (if used), plugging radiator tubes & eroding water pump seals and impellers. There’s a good reason why the new PHOAT coolants have the ability to go 10 years/150,000 miles, or more, without cooling system problems.
 
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