What is this tan coating in my radiator and hoses? (pics)

Noticed my temperature gauge near the red (normally sits about 50-60%). Looked in my radiator and saw this. Tan coating covering everything with some lighter color stuff plugging up many of the tubes that carry the water down the radiator.
Looking through the radiator cap hole (flashlight partially blocking view).


The coolant outlet from the engine has the same tan coating. The coating adheres to the metal pretty well. If you scrape some off, it comes off in chips and is a thin but hard material.


The bottom hose of the radiator and the radiator bottom outlet look very clean... no tan crud.

Here is where it gets weird. The upper radiator hose that is between these two places with the tan crud has a coating of red rust color stuff and it is very sandy/gritty feeling.



The water/coolant was very tan/yellow too. I drained the coolant, filled with distilled water (almost 2 gallons), and drove a bit to circulate. I repeated that again. Water was a lot better (more clear with a tan tint). I replaced the radiator this evening and will use another vehicle to get new hoses tomorrow.

The history on it is a Toyota dealer replaced the timing belt and water pump at about 180k miles. A month later my original radiator developed a leak so I replaced it with Spectrum Premium radiator. Since the coolant was new (they used Toytoa red), I drained it into a clean bucket and reused it. I only had to add a little water to bring it to full (I assume I used distilled). I used new OEM upper and lower radiator hoses.
It ran fine for three years (about 215k miles now) and this is what is going on now.
The motor oil is at the right level and looks perfect.
The transmission fluid is a little high, but looks fine (T-IV pink/red with a little darkness). No milkiness or strawberry milkshake anywhere.

Anyone have an idea of what the tan coating is from?
Thanks,
Matt

 

My first guess is maybe something was in your replacement radiator that reacted with the coolant but the fact it worked fine for 3 years would almost have to rule that out

Trans fluid is good not losing engine oil .

It does not take much oil to make a big milkshake type mess when mixed with coolant.

I am guessing no one worked on your truck that might have added any sort of stop leak product .

Any one jealous or mad that might have done something ??

First time any type of over heating issue since the radiator was replaced ??

What ever happened it happened now.

Best of luck.

 

pull the spark plugs.......keep them in order

have a close look at em

if U cant account that any1 else has been fiddling/working on Ur engine

i suspect water is mixing with oil likely under intake

 

Appears to be the outcome of a blown head gasket... assuming a head and or block are not cracked.

 

Thanks everyone for the replies. I haven't used stop leak in a few decades, but yes it does kind of look like stop leak. Other than the water pump/timing belt and Valvoline drive through oil changes (where I can see what is going on), I do all the maintenance and repairs (which fortunately has only been things like shocks, O2 or MAF sensors, yearly drain and fill of transmission fluid). She sits tucked into the garage every night. I have never come out to find the hood open. This is the first time it over heated. I smelled the coolant when the original radiator developed a small crack so it never over heated before up until now.

I guess some kind of reaction is possible with the radiator and the coolant from the Toyota dealer. Head gasket seems like a possibility. I will monitor the fluid every few days to see if it starts changing colors. Does a head gasket leak with either oil or exhaust gasses getting into the coolant normally make for milky streaky coolant? The fluid was a uniform tan and not milky at all. It is almost time to replace the plugs so I will look for weirdness on any of them when I replace them.

Would the best way to determine if I have a head gasket leak (while the engine is together) be a tester like this?

$37 Block Tester BT-500 Head Gasket Combustion Leak Test Kit - Made in USA

https://www.amazon.com/Block-Tester...ds=head+gasket+test+kit&qid=1602866363&sr=8-2

 

best way is to compression test

then likely a ‘ leak down ‘ test

i sure U take very good care of Ur vehicle.......not the issue

Ur trouble doesnt come from neglect or abuse

pull thw plugs 1st..................keep them in order NOT a jumble

the suspect cylinder might be obvious

otherwise the prev mentioned tests usually reveal

 

Looking forward to how this plays out.

Head gaskets can fail in several ways .

Coolant into a cylinder

cylinder to cylinder .

oil into coolant because oil pressure is higher.

It really does not look like oil then I never saw Synthetic oil mixed with coolant .

Do you use Synthetic Oil or regular ??

It would not take much oil 1/2 a quart.

 

Easy way to tell if it’s a head gasket is take off the radiator cap. Start the truck. Watch for small bubbles. If you see bubbles. The bubbles are exhaust gases coming out through the radiator.

 

I will update when I have more info. I assume the radiator will take care of my overheating issue based on how plugged up the radiator was. I'll probably drive it for a few days to see if the fresh water/coolant changes and if so how quickly. I am mostly working from home these days so it may take awhile before I get any miles on her.
I use conventional oil. Never used synthetic.
Thanks ROAD DOG for the suggestion of pressure test and leak down. That sounds like the way to know for sure if it is gasket/block.

When I did the two drain and fills with distilled water, I would keep the radiator cap off until I could see fluid movement. I never saw any air bubbles come up. I used the Torque app to monitor the coolant temperature and as expected right about 180F I would see the water start flowing.

 

When my head gasket went in my 2005 before we did the Block Tester we did the Air Bubble test. We saw the Air Bubbles almost right after starting the truck. Just to be sure we did the Block Tester and both tests showed I had a Head Gasket issue.

 

Did you ever see and white crusty material around the cap of your overflow bottle? Or did you ever hear boiling in your overflow bottle when you shut the truck off?

 

The tan stuff that is suspended in the water turns a bit white when it dries on a surface, but there was no sign of white crust on the radiator or overflow when I first looked at it. I have not seen any bubbles or heard any bubbling (before or after the thermostat opens). If there is a head gasket problem, it doesn't appear to be from the exhaust to the coolant.

The new radiator and hoses are in and the temperature looks good. It is now 192-195F even with the AC on during a 90+F degree day. I've done two fill and drains with the new radiator in, but the water turns tan again after I drive it for 10 minutes. It doesn't seem to be getting better with each drain and fill which makes me think something is consistently adding the tan stuff to the water.
I am going to have a family acquaintance who is an experienced mechanic look at it. If there is a head gasket problem, that is more than I want to take on so I would have them repair it or at least diagnose so I can decide if the cost is worth it. She is in good shape still so I would drop some coin to get her fixed.

 

oil + coolant + = milkshake

where the 2 are mixing remains to be seen

this time o year keep water drain going ............ No chance o freeze up loosong the block or head

the temp changes from driving

something expands allowing a crack/hole ( device ) to release fluid allowing both to mix

resulting in the milkshake

 

How many miles are on the motor?

 

It says 215k miles in the first post

 

Last summer (2019) some kids working for us checked the coolant in my Sienna and forgot to put the cap back on.

It of course blew out all the coolant but strangely, the gauge never showed hot. It started clattering and when I turned on the heater to feel how hot it was blowing, was just cool air. Hmmm, pulled over and it was horrible sounding. Nothing but brown mud in radiator and looked like lime dust under hood. (our similarity)

I actually put it in shop and told them to test every which way they could and get ready to just replace engine. Flushed/Refilled it and everything checked out. Blew me away that it wasn't a major meltdown.

It's likely it's hurt but you may luck out.

edit: Oh yeah. Most important. The brown stuff. It was oil. Intake had warped some and was allowing a but past. It also had knocked and rattled so hard it broke the knock sensors. Found a water leak there afterward while changing those. (cap was still cause though) I just had forgot after expecting the worst.

 

It can very well be only a small amount of oil getting in the coolant. So Your not really seeing a major oil loss yet

If this is the 3.4 and has a oil cooler I would look very close at the cooler.

The more oil getting in the coolant the thicker it gets

I had a major failure of a oil cooler I can only say about as thick as peanut butter but more grit and grainy appearance.

 

Can you tell me more about the oil cooler? Yes, it is the 3.4L. I did some searching and saw references to an oil cooler near the oil filter. I looked around and see a hose coming off the engine about where the thermostat is and it runs back to what looks like a cylinder that sticks sideways out of the engine. I was looking for a radiator type device, but didn't find one.
OK, found a good diagram posted by someone on TW. Yes, I have an oil cooler. One more place for oil and water to mix. I let the drained water settle overnight and it does look like oil.
That is an expensive part, $500 to $800 depending on the place selling it.
https://parts.toyota.com/p/Toyota_2...AT/Engine-Oil-Cooler/62995838/1571062050.html
If this is the place of mixing, could it just be a gasket or o-ring? It sounds like there is a coil in there that the water circulates through to cool the oil.




Thanks,
Matt

 

gasket or oring In that case your more likely to have an external leak

It can also be a cracked head from an oil passage to coolant passage

Just an idea something to think about.

Cooling system pressure test .

 

Update: It will take time to know for sure, but I talked to both the acquaintance mechanic and TW member Speedfreak (well known in the San Diego area). They were both busy, but nice enough to talk to me about what I was seeing and asked me questions. Both thought it was rust and not oil (based on the questions they asked me and my answers about what I saw in the radiator and drained coolant). It took a few more drain and fills, but eventually the distilled water started to get more clear each time. I used Thermocure in the system for two days (rust remover). It is a interesting product that is a "selective chelation" and reacts to iron oxide.
I then did two more drain, fill, and drives (heater on) after Thermocure and the water got very clear. I finally put in the Toytoa red and the distilled water. It is looking nice for now and I will keep an eye on the coolant.

Getting jiggy with the jiggler. Here you see the jiggler as I found it between 12 and 1 o'clock.

Although unrelated to my tan coolant, I had a lot of time with monitoring the coolant temperature with the Torque app during my drives after a fill. The new radiator did wonders, but it seemed to be running a bit warmer than what other 3.4L owners are seeing. I read it was common to have even the Toyota dealer install the thermostat with the jiggler at 12 o'clock instead 6 o'clock. The last radiator trapped most of the tan stuff along the top and left the lower radiator hose pretty clean, but I thought it wouldn't hurt to replace the thermostat and while I was in there check the jiggler position.
Sure enough, I found the Jiggler at 12 o'clock. It was replaced when the Toyota dealer replaced my timing belt and water pump three years ago.

There aren't any stops the last mile to my house so I turned off the heater, drove that last mile, and captured the temperature right before I pulled off the main road.

Thermostat with jiggler at 12-ish o'clock.


After new thermostat with jiggler at 6 o'clock.


With the jiggler at 12, the coolant temperature varied much more. While driving at >25MPH, the coolant temp varied between 192F and 199F. With the new thermostat and jiggler at 6 and >25MPH, the coolant hardly varied at all. I did the same test with just distilled water and then again with distilled and Toyota red. Both tests had the exact same temperature after that mile.... one at 5PM and one at 10PM.
Many people say they see a 10F improvement in temperature when they change the thermostat jiggler from wrong to 6 o'clock. I am a believer now.