Just moved from NH to WA. Took the 4Runner to a shop to get a once-over and oil change after the 3100mi trip. Struggling with a few pieces of information the shop came back with, and I'm curious to know peoples opinions, specifically on the topic of radiator failure between the trans cooler and main radiator loops.

The shop owner, who otherwise seems quite competent and straightforward, has expressed concerns that the radiator is failing because:

1. The radiator fluid (genuine Toyota coolant) is very low, apparently the resevoir was empty and they added a bit to raise the level
2. The transmission fluid is very high, about 2in further up the dipstick from where it's supposed to be
3. The radiator fluid is oily and has a thick consistency

However, as far as I understand it, the coolant and transmission fluid are highly incompatible and react when combined (milkshake). There's no sign of that whatsoever, no opaqueness to the fluid (just oilyness) and no change in temperatures. Furthermore, I replaced the radiator (Denso) just last year. It's not genuine Toyota, but I still find it hard to believe it's failed internally in just a year.

My personal take is that this is a 180k mi vehicle and the reservoir is just dirty. The coolant fluid has a thick-ish and oily-ish consistency to begin with. It's also quite possible that transmission fluid was added a while back when I was having stuttering issues (that ultimately went away with a timing belt and full tuneup and likely had nothing to do with the transmission).

I'm thinking top off radiator and call it good. Do a dropped pan transmission tuneup (filter, bands?, etc.) and reset the fluid level when I can.

It also set me off a bit that this shop owner came to me and told me this vehicle has the worst rust he's ever seen. It's an 18yr old vehicle from NH, so yea, it's got rust, but I climbed under just to double check, it's very solid and significantly more so than many vehicles I've owned and driven. It also got a clean bill of health from a shop that I trust in NH before the trip cross country, and this new shop is telling me that it's unsafe and dangerous and going to kill me. It's definitely not (frame is solid, even still has paint in most places, mounts for engine, body, etc. are all solid).

Change the radiator and flush the coolant. West coast mechanics don’t know shit about rust. They see a rusty bolt head and think your vehicle is junk.

Generally when the radiator fails and you get a pink milk shake, its pretty obvious within miles of it happening. Your truck will start to over heat, the transmission will start slipping etc. The coolant will be cloudy and look like......a pink milk shake. It doesn't take much tranny fluid to make the coolant turn cloudy, so even a little will do it.

If you haven't experienced any of those symptoms, you are "probably" fine.

Did he check the tranny fluid level after it was brought up to operating temperature (ATF at 160deg ish), while it was in park running?

If I had to guess, your tranny fluid was probably overfilled (it happens). And you probably have a small coolant leak somewhere (it happens).

For piece of mind, you could certainly do a drain/fill of your tranny fluid. This way if your fluid level was high, you can get it back to where it should be. If you want, you can change the filter ( I suggest an OEM one and a rubber gasket for the pan). I would pressure test your cooling system and see if you can find a leak.

Don't know about his first round of checks, but he brought me out to the car in the parking lot and showed me the level on the dipstick (which yea, it's high). I doubt the transmission was overly warm as they didn't road test.

During the trip cross country my mother-in-law reported the exhaust got really loud and check engine light came on. This same shop told me there was a massive hole in the exhaust where the O2 bung (downstream) is located and we'd need a new one. I crawled under and... all that happened is the O2 sensor nuts rusted or fell off. I put it back in and re-secured it and voila, quieted down and passed emissions on the first try. Got a quote to replace the segment of pipe of $300-800, fixed it for ~75c. Not confidence-inspiring.

Has your radiator ever been replaced ? If not it's only $100 so I would do it. I am assuming this is an automatic transmission ?

Fact.

He said the radiator was replaced (Denso) last year. It's part of the reason why I doubt it has failed.

Anything is possible though...

Yes, replaced with a Denso unit last year. I really doubt it failed in that time but who knows.

It's the 2000 Limited from my signature, so yes, it's an automatic (and the multi-mode auto specifically). IIRC, manual doesn't use the cooler in the radiator, so wouldn't even be a concern.

I did the radiator replacement myself. Now that I'm thinking this through, I can probably pop off the line from the bottom of the radiator to drain the trans fluid without dropping the pan... not sure how good an idea that is though.


Truth is, I'm just trying to get through the year. Planning to replace next year and move on from 4Runners. This has been a very solid and reliable car, but at 180k it's getting a little long in the tooth and I'm ready for something with a bit more creature comforts and a bit more on-road capability (yes at the expense of off-road). '05-08 Cayenne Turbo S here I come .

If you want to eliminate the possibility of the pink milkshake, install a separate transmission cooler and bypass the rad. altogether.

If you are worried about overspending (paying someone else) to maintain your 4runner, I do not recommend moving up to anything from Germany. Especially a P-car. This comes from the perspective of a 100% DIY'r for 30 years with two C5 Audi's in the fleet to maintain.

From my experience, a 10-15 year old Euro feels longer in the tooth than a 20-25 year old 4Runner ever will. The Cayenne Turbo is such a blast but it will make your life a lot more complex too. Considering your pre-req to it is the 4Runner, you are in for some nasty surprises. 4Runner reliability spoils you rotten. I'd keep the 4Runner parked on the side for the days the Cayenne is MIA.