Radiator Fluid turning to Silly Puddy

Has anyone ever seen radiator fluid turn to tan, stringy Silly Puddy? We had a fluid exchange done on our Radiator and it happened to us within a week of that. The shop says it was caused by transmission fluid leaking into the radiator. However, our transmission fluid is full and the radiator was over half full of goo. (close to 4 gallons). We suspect a bad mix of two different coolants but the shop won’t even consider that option as a cause.

It usually is either transmission fluid or engine oil. The latter should be checked for foaming, also remove the oil fill cap and look under it for gunk. How does the transmission fluid look? Any other signs of trouble, misfire, check engine light? Other suspects are intake manifold. Also need make/model/year of the car.

I’ve never seen it first hand, but I’ve heard that mixing coolant types together can cause the coolant to gel. If your engine oil and transmission fluid are both OK what else can it be?

When switching coolant types a thorough flush of the cooling system is required.

I’ve no experience at all with coolant doing this, but like Mcp I have heard that mixing can create weird issues. In particular I have heard that mixing Dex-Cool with regular green antifreeze can create a weird kind of gel.

The reason that I don’t really find this plausible, and probably the reason that the shop isn’t looking at it seriously is that almost all shops use newer “global” antifreeze/coolants that are good in virtually all vehicles, and mix with any other kind of coolant. At least those are the claims of the manufacturers of global coolants.

What kind of coolant did the shop use when they performed this service?

The car is a Dodge Caravan 1999. The transmission fluid looks full and fine, the oil is full and fine too. No signs of gunk in either. The car was running great until it overheated. The coolant the shop used they have just began using there. It is a “universal” coolant and is a yellow and is a denser fluid than the old green stuff. We had the old fashioned green type in there before the coolant exchange. Thanks for your comments.

What did they determine as the cause of the overheating?

I have seen some severe sludge in an Oldsmobile with Dexcool, and it was due to the infamous intake manifold gasket/Dexcool issue. I assume the sole cause here of overheating was the sludge/goo is so bad that it prevented the coolant from doing its job properly.

It has been said in other forums that some of these “all makes” antifreezes are “Dex clones”, and have the apparent offending ingredient that causes Dexcool sludge (in combination with air exposure), and may exhibit the same characteristics as Dexcool, to include sludging when air is introduced into the cooling system via an intake manifold leak or some other source.

I think a lot hinges on the radiator fluid exchange, and how well the system was flushed before the new universal coolant was installed. I would take a step back, and get the vehicle flushed with a cleaner, flushed with water multiple times, and filled with Zerex green. It is the same formula as what worked before in this car and is approved by Chrysler for this car. I mention by name because the Zerex line retains the chemical qualities of the three major antifreeze types on the market (G-05, Dexcool, regular old green), so Zerex green is the closest you can come to the old green that is quickly disappearing in favor of the universal. Peak green may also work, but I am less sure of its actual chemistry and reputation. You could use Motorcraft green, or a G-05 (Zerex, John Deere, Motorcraft yellow) formula and achieve the same results, but these fluid s are far more expensive than Zerex green.

If necessary, I would find another shop if this shop doesn’t want to do this. Then I would monitor the vehicle and see if I really have other issues such as trans fluid or oil getting into the radiator.

If this happened to me, this is the approach I would take at this time. It gets the car back out on the road and starts a period of watchful waiting to see if there are other issues that need to be dealt with.

Since the car overheated maybe this sludge is caused by engine oil mixing with the coolant due to a leaking head gasket.

How is engine oil consumption? It does not take much oil in the radiator to create a mess like this.

How many miles on the vehicle? And is this the first coolant exchange performed since new?


Another additional information request, what kind of coolant? I know there are warnings about mixing long life coolant with non long life coolant, my feeling is this mixing returns the long life coolant back to non long life coolant in terms of lifespan. I don’t see geling from mixing coolants.

I have seen the “organic” orange coolant turn into what you describe when a little oil mixed with the coolant. A tiny head gasket leak turned the coolant into what looked like toothpaste.

Here is what was said:
It is a “universal” coolant and is a yellow and is a denser fluid than the old green stuff.

I assumed a generic or Prestone brand universal/all makes, all models fluid. I did not understand the “denser” part, though, because I have not seen any major difference in density of any of the coolants.

I have read about the potential of sludge when mixing, but like you thought the only major effect was that long life lost its “long life” abilities.