Radiator design?

[maestro123]

Just wondering what people's thoughts on the Toyota's design of the radiator on the Previa, particularly how the radiator cap is on the reservoir rather than the radiator itself. Is this a common design? What's the reasoning behind it? I did a little searching around, and I believe the Sienna also has the same design, so I guess it's not terribly uncommon. For me, I actually like it when the cap is on the radiator itself, so it's easier to check if the radiator is bone dry. Thoughts?

[TheMAN]

its purpose is to ensure air is completely purged from the cooling system... without doing this, the heater core is the highest point of the cooling system, trapping air... this will cause cavitation and engine overheat... with the reservoir where it is, it makes it the highest point of the cooling system
your preference for liking the cap on the radiator is one thing, but it makes no sense when you say it's easier to check if the radiator is bone dry... if the radiator is "dry", then the reservoir will be empty! This tank is not really a reservoir but a "surge tank"... it's completely pressurized and coolant circulates through it any time the engine is running... it is NOT an overflow tank!

[maestro123]

your preference for liking the cap on the radiator is one thing, but it makes no sense when you say it's easier to check if the radiator is bone dry... if the radiator is "dry", then the reservoir will be empty!

I had an issue with my Previa where I had a full coolant reservoir, but my radiator was completely empty. And I got a blown HG out of it. :cry: That always seemed rather mysterious to me, so I had to do a bit of searching and found out that apparently it's not uncommon for the small outlet ports at the bottom of the reservoir to get clogged.

From http://www.toyotavantech.com/forum/showthread.php?1885-97-s-c-Head-gasket-replacement-summary-W-part-s&p=11337&viewfull=1#post11337



-the most common culprit to headgasket failure was a clogged return cooling line. He had mentioned that the majority of Previas he had worked on had crud in the cooling line that ran from the reservoir back to the engine... causing insufficient coolant flow.


That's exactly what happened to me. I had mud and black flakes clogging up the coolant outlet port. Also turned out to be the same issue as 2 other guys in this TN thread.

http://www.toyotanation.com/forum/85-previa-forum/1092545-previa-engine-block-coolant-drain-plug.html

It seems like one of those single point of failure type of things, so that's why I asked about the whole radiator bit. If I had been able to more easily tell there was nothing in my radiator, I might have been able to avoid the blown HG. Your explanation about the reservoir being the highest point so that air can be purged did make sense to me though.

Hypothetically, if the cooling outlet ports were bigger so there wouldn't be a clog and taking that out of the equation, is the surge tank design better than the overflow tank design? Is there a reason they don't just make it the same, say, as a Toyota Camry?

[TheMAN]

This is a non-issue if:
A) Proper phosphate based coolant, formulated for Japanese cars. Everyone's favorite yellow bottled Prestone does not apply, it is silicate based and causes both water pump wear and sedimentation
B) Usage of distilled water instead of tap water. Using tap water is one of the worst things anyone can do to a car because tap water causes severe sedimentation over time and reduces coolant life due to ionization from the water's impurities. Ionization causes electrolysis, causing aluminum parts wear (cylinder head, radiator, heater core, etc)... Hardly anyone gives this a thought because the manual doesn't mention it. It is assumed tap water is "good", which is an OK assumption for Japan due to their high quality tap water, but not in America, not in other countries due to the varying levels of hardness and cleanliness!
C) Not changing the coolant at the scheduled intervals... 30000 miles (50000km) or 2 years, which ever comes first

My van was improperly serviced before by bad shops.... they used tap water, and at one point in time, they flushed the system using a garden hose attachment you buy at the parts store, not using a real professional machine that attaches to the radiator cap spout... the coolant tank was never flushed... Once I've taken all maintenance and service on the van years later, I found out there was significant sediment in the coolant tank. I managed to flush it using lots of water blasting, adding a bit of cooling system flush into the tank, and shaking the crap out of the tank (with the nipples capped off) and dumping it out... I never got everything out but got it to an acceptable level... It did take basically the entire bottle of the flush agent this way... eventually I removed that stupid garden hose crap and restored that heater hose back to the factory one too (was not cheap)

Ever since then, I've always used distilled water... I first switched to Motorcraft coolant as back then I knew little about coolants, then once I've learned of the different chemistries of coolant, I've used Subaru coolant as it's dark green and I have a huge stash of this... same exact stuff Mazda uses at the factory before... same formulation as the old Toyota red coolant, other than the dye.... Anyhow, the switch to distilled water cut down on the sedimentation a lot... and ever since I've been using the proper Japanese coolants, I don't recall seeing any much or further build up of sediments in the coolant tank, nor any upper build up that typically caused by foaming above the coolant... I'll check next year when I change the coolant again

Everything has still been working great (knocks on wood)... I can hear gurgling when pouring fresh coolant in, and it doesn't take much effort or time to completely purge it of air (I always pour slowly)... just squeezing the radiator hoses helps, and running the engine at 2000rpm helps... driving around the block while carefully monitoring the temperature also helps

You will know you have air in the system if your heater doesn't work well, hear a "water splash" sound when driving around, and the temperature gauge behaves weirdly... this is especially true if you didn't get quite near 2 gallons of mixed coolant into the system!

[maestro123]

Yah, I think that mud/sedimentation must have come from my using regular Prestone green coolant with tap water. The black flakes, I'm not sure. Maybe a deteriorating hose? I've read that Supercharged Previas had a problem with black flakes in coolant, but I don't actually have S/C Previa.

I wouldn't be surprised if most mechanic shops just use tap water. But then again I wouldn't know, since I've never asked. Just seems like it might be too much of a hassle for them, and I've never seen distilled water containers lying around in the ones that I've been to.

Is Toyota Red LLC the official good coolant to use with our Previas? I used to use the $12 Prestone regular green concentrate, but I'd be willing to spend a bit more if it's better for our vehicles.

[TheMAN]

the black flakes may have come from the silicate based coolant (meant for domestics... the classic yellow bottle prestone) tearing away at various coatings in the cooling system... Japanese manufacturers claim that silicates are abrasive to water pump seals and bearings... after seeing how much longer water pumps last when the proper phosphate based Japanese coolants are used, I believe this!

all shops pretty much use tap water... it's cheap, gets the job done then, and they don't care about your car... at best, you'll get filtered water
want to do it right? DIY!!! This ridiculousness is why OEMs have switched to the "long life" coolants about 10 years ago, they all come in premixed jugs so that mechanics can't screw it all up... 1) the ratio will be correct 2) there won't be contaminants 3) so they can make more money off coolant, both from higher price per gallon and needing to buy at least 2 gallons at any time (fortunately, you only need to change this after so many miles and years, so the cost per year is actually cheaper)

and yes, Toyota red is what's meant for the van.... I honestly have no idea what color it was back in the days when it left the showroom floor... anyone who remember this? I'll continue to use the Subaru stuff though as I have a bunch... it's really the same stuff but dark green instead... the Mazda stuff (long life, not extended life FL22) is exactly the same as the Subaru ones too
If you want to switch back to Toyota red, DO flush the system completely first... I wouldn't hook up a garden hose to it... just buy a bunch of distilled water... drain the system as much as you can (from the engine block and the radiator), refill with straight distilled water... repeat 3 times, then refill with Toyota red, at slightly more than half part since there would still be some water left inside, such as in the heater core.... I would also remove the coolant tank and flush it out (no choice but to use tap water), or just replace it outright with new


but, I'll continue to use the cheap green stuff for my corolla beater... car was bought cheap and was already abused... no sense giving it a royal treatment when it's so much easier to work on!

[cb97alltrac]

Reviving an old thread on coolant and overflow tank design. Both of my previas I have purchased recently have had at least one of the 3 small tubes off the bottom of the reservoir tank occluded by black flakes, rubber debris, which I believe results in no flow thru the tank which cant be good for the cooling system. This is the first thing I check after purchase. The most rear tube goes back and down and was the one occluded. The other 2 were just dirty. Others have reported low radiator coolant with the reservoir full with the above the likely culprit. I always now use toyota red with distilled water after 4 distilled water fills and drains with the heater on high and also draining the engine draincock which is 10mm and vertically oriented and is located by the oilpan. If you havent changed your coolant in the last year I would check these reservoir tubes after draining the radiator.
The engine was high idleing on both these vans, which stopped after cleaning the black flakes from the coolant tube to the throttle body which is located in front and below the masss air flow sensor , drivers side under the hood. Coolant is in the outer part of this two channel tube, cleaned it carefully with a toothpick. Horizontally oriented, this has been described by cytroger and others.

[Ace MM]

If the cap was on the radiator, it would be hard to reach.
The cap just needs to be the high point to purge the air.


DIY!!! This ridiculousness is why OEMs have switched to the "long life" coolants about 10 years ago, they all come in premixed jugs so that mechanics can't screw it all up... 1) the ratio will be correct 2) there won't be contaminants 3) so they can make more money off coolant,
and yes, Toyota red is what's meant for the van.... I honestly have no idea what color it was back in the days when it left the showroom floor... anyone who remember this?
Premixed....$$$$$
A gallon of distilled water is .99 mix with 1 gallon red and enough left over to top off for the rest of the summer.
BTW, do not steam drain it by accidentally leaving the cap off and running the A/C, not a good idea :wall:

My 88 pickup had red. That's when I learned about the differences.
My Datsuns use green, 85,000mi on the weak water pump. Toyota always red.