peterls

I've been lurking around here for a while and appreciate all the info that is available. Some of you guys really know your stuff...
One thing that I recently discovered, and that may explain some (many?) of the cooling fan problems that people have, is the elusive "ECT" (in Lexus lingo) switch. Yes, it is confusing as it sounds exactly like the "ECT" switch that is near the shifter... but it is not that at all. I guess outside of the Lexus factory, everyday folks refer to it as "cooling fan switch" which is what it is.

This switch can (and will) go bad, and unless you drive in stop and go traffic in California like i do, you may not even notice that it is not working. It is supposed to turn on the electric fans in case the coolant reaches temperature over 185F.

I have a 1990 LS400, and while my temperature never went really high, it did crawl ever so slightly above that second white line, at which time I noticed that electric fans did not turn on.

So I researched possible reasons, and the way to quickly diagnose the problem, to see if it is indeed the infamous Engine Coolant Temperature Switch, is to go under the car, and find the electrical connector that is going to the switch itself. It is on the driver's side of the lower corner of the radiator. It may be a little hard to find at first because there is a big black metal "something" hiding it - it seems like a guard for steering or suspension, can't quite tell (don't have a lift, I just stuck my head under the car).
With the car well warmed up (above 185F coolant temperature), turn the ignition key to "ON", disconnect the temperature switch, and the fans should come on instantly - you will hear them no mistake about it. The connector may seem hard to pull, but it is because it is somewhat deceptive in the way it looks: you are probably pulling on the wrong part, before the little, visible gap... but the gap is actually part of the connector (the connector itself is made of two parts - what seems to be the coolant fan switch part is actually still part off the connector)! The right way to disconnect is to press the little thingamajig on the connector, and pull it all together. The fan switch does not stick out very much at all from the radiator.

If the fans come on, that means your ECT switch (in Lexus lingo) is shot.
And that's my case.

Now, where I am stumped is that I have been searching high and low all over the internet, found even sites which have posted PDFs of service manuals, and NONE of those say anything about how to change the coolant fan switch.
If the switch was easily accessible, it would be a no brainer. But, I am not exactly a pro, and don't dare get in there without knowing what exactly I should remove (besides the obvious such as - work on a cold car, and drain all the coolant first). It was hard for me to even reach the cooling fan switch with my fingers, just to disconnect and reconnect it for the test... but to fit a ratchet in there would be impossible. The metal part that is covering it, I can't quite see what it is holding, and where all the screws are... so if anyone has done this, or maybe has the same car and can take a look and tell me what they think is the proper procedure, I would really appreciate it!

Cheers
ps. I promise to post a photo tutorial, if someone gives me some guidance

LScowboyLS

The service manual calls this the water temperature switch, and it has been a while since I changed one, but if you are fortunate enough to have a pretty deep set of hand tools, I don't remember anything having to come off in order to change out the water temp. switch. (keep in mind I have a lot of weird wrenches, ratchets, etc. - so someone without these may have to remove some things to get to it)

Seems as though I did it from the bottom, if memory serves

peterls

Thank you LScowboyLS for the quick reply. I too have seen it called "water temperature switch" or some just call it fan switch...

I have some deep sockets, but don't even know what size I need (mine mostly go up to 19mm), but I would probably need one of those fancy double-jointed, whathaveya, to be able to get at it... just don't have the time to go back an forth, I'd rather prepare myself with right set of tools first.

For those who are wondering what this "ECT switch" is - it is a simple thermostat set to send a signal when temperature of the coolant exceeds 185 F. At that point, once the signal is sent, the two electric fans should come on at the highest speed (higher than when you turn on the A/C), and once the temperature of the coolant drops below the 185F, the switch reacts again, and the fans are turned off.

LScowboyLS

it actually turns off the fans at 181°F and connects them at 199°F

see the service manual explanation

oh, and what year is your LS ?

peterls

Thanks for keeping me honest (about the temperatures)

Mine is a 1990 LS400, with just over 150k miles on it. Bought it a few months ago. It was well maintained (serviced at a dealership for most of its life). From what I gather, engine and transmission are perfect. But there are all these little things I want to take care of (this fan switch being one of them)... I already did the temperature sensor to try and improve my mileage, but it made no difference.
Currently getting around 17.5 mpg mixed city and highway (although it is all steep hills where I live, and quite a bit of traffic even on the highway, so no point in using the cruise control)... was hoping for a little better. Being in California, our gas is a little weaker with more ethanol so that may be the reason too. Also did all four O2 sensors (Denso=oem), with a help of a friend as one was badly stuck. Major tip: besides your chemical spray of choice, use plumber's pipe wrench! That one stubborn o2 gave in when we attacked it with the pipe wrench.

Changed oil about 2000 miles ago, and can't believe that it is as clean as water. I mean, I can hardly read it on the stick that's how clean it is.

I looked in service manuals, and it does not say anything about how to change the switch. It just shows its location... Perhaps I should just bite the bullet and buy a little ratchet joint and go with that?

LScowboyLS

O2 sensor FYI

the two post-cat O2 sensors are known as the "tattletale" sensors, they are there to narc on you for being a polluter, but they actually have no input whatsoever on how the car runs, they simply set the check engine light and store a code if you have been being an emissions bad boy! - the car otherwise doesn't even know they exist, the ECU doesn't care!

So in a pinch, in a city with no emissions testing or required compliance, the LS400 owner who is short on funds or selfish about the environment can safely ignore them.

peterls

Oh I know that, I was just being a nice guy - especially here in California where pollution laws are quite harsh... and since I got them for $50 for both, and was already under the car and the original ones were never changed, it made sense.

Back to original topic - if anyone has changed the fan switch sensor, at the bottom of the radiator, let me know how you did it - what tools you used and so on.

nthach

in 1st gen LS400s, there are 3 sensors - the ECT sensor underneath the passenger side ignition coil, the thermo-time switch in the thermostat housing which is the on/off switch for the cold start injector(Toyota got rid of this in later cars) and a secondary ECT sensor for the fans in the radiator. They can be removed carefully with a socket.

peterls

OK, just came back to report that I replaced it and it was not as bad as I thought initially. Deep socket and an extension is all it takes. A socket joint might help but is not necessary. It is a little tight, you may want to try from the other side, as it can be reached from both sides... whatever works for you I guess.

I replaced my ECT switch (engine coolant temp switch), thermostat, and at the same time noticed that the little vacuum controlled "ported vacuum switch" (p.n. 90925-05068) had the two little nipples so brittle that they separated from the hoses (couldn't tell if they were like that all this time, or if I broke them as I was working there) so I replaced that as well. Then I used "Prestone 2in1 coolant flush" (bought at walmart) which can be left in the engine for a few days, and I have to say I am really happy with results!

Before I did all this, the engine temperature was reading as just fine. But, it was taking too long to warm-up (bad thermostat), and above all - engine was running rough and transmission was shifting poorely, too late often and with a jerk. I figured that the cooling system was dirty and that engine was not being cooled uniformly including the AT fluid which was obviously too hot (which is why I wanted t to do this ASAP), hence the Prestone flush and all of those problems are gone. (I could figure that out by the fact that previous owner used green coolant - so NO to green crap! Don't do it!)

LScowboyLS

hopefully you used the real Toyota red coolant, it will make your $600 radiator last almost forever!

peterls

Oh you can bet I did! The previous owner used green stuff... I just don't get it- how hard is it to use the real thing??? Anyhow, I ran a bottle of Prestone 2in1 coolant flush, which they say can stay in the cooling system for a few days, or about 5-6 hrs of driving, and I left it there for just that amount of time, and then flushed it out. Brown stuff came out - it was a color of coffee almost! I flushed it again with distilled water, until it became clear, and finally refilled it with 50-50 mixture. You can buy either concentrated Toyota coolant or pre-mixed. I opted for concentrated Toyota coolant and mixed it 50-50 with distilled water. It takes almost 3 gallons all together, maybe 2.7 or so. But the engine and AT are running much better now; I am sure that there were some narrow passages where coolant was not flowing properly so AT was not getting cooled and possibly some parts of the block... but now it is really nice. I love it when I get it right like that