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Thermostat question

Old 03-17-2019, 10:36 PM
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Thermostat question

Hello all,

I am wondering if my thermostat is working as it should.Here is the situation:

1991 4runner, 3vze V6 engine, 4wd. When engine is cold, it warms up when driving in about 6-10 min. Arrow is getting to a little before half way (80-something degrees - 180-185 farenheit) and stays there, no movement at all. So I drive around 20-30 miles and I check the hoses. All upper hoses are hot, so is the radiator, but the bottom hose, coming from the radiator is just warm. Infact so "ok warm", that can hold it easy with my hand and I wouldnt get hot never. So I guess the temp there is no more than 30-36 degress (95 farenheit). Nothing is boiling, no steam or smoke. Is all this normal, or should I replace the thermostat? Sorry if its a dumb question, I aint very skilled at cars yet, but willing to learn
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Old 03-18-2019, 03:32 AM
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Originally Posted by Dilomski View Post
Hello all,

I am wondering if my thermostat is working as it should.Here is the situation:

1991 4runner, 3vze V6 engine, 4wd. When engine is cold, it warms up when driving in about 6-10 min. Arrow is getting to a little before half way (80-something degrees - 180-185 farenheit) and stays there, no movement at all. So I drive around 20-30 miles and I check the hoses. All upper hoses are hot, so is the radiator, but the bottom hose, coming from the radiator is just warm. Infact so "ok warm", that can hold it easy with my hand and I wouldnt get hot never. So I guess the temp there is no more than 30-36 degress (95 farenheit). Nothing is boiling, no steam or smoke. Is all this normal, or should I replace the thermostat? Sorry if its a dumb question, I aint very skilled at cars yet, but willing to learn
the lower hose is the supply line; it is supposed to be cooler than the upper return line. if it was as hot as the upper hose, the radiator isn’t doing its job or the thermostat is stuck open and the radiator can’t do its job.
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Old 03-18-2019, 04:36 AM
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This is how it should be. Go drive up a long ass hill for 5 minutes at 60 MPH. Then the bottom hose will be warmer. Probably.

The thermostat opens when the engine gets to hot and lets cool water in (the pump sucks it and pushes it though the engine, past the thermostat and into the top of the radiator.
It closes up again when the engine gets cooler. A temperature sensor (ECU coolant sensor) will tell the engine computer (ECU) what temp the coolant is as well.
Has nothing to do with the mechanical regulator aka thermostat, but only if the temp is correct will it run correctly instead of in "limp" mode.

EDIT: ONCE AGAIN I PRETENDED OTHER ENGINES THAN THE 22-RE don't exist. Part numbers will NOT fit a 3vze
Now, if you are feeling fancy schmanzy and have 50 bucks burning a hole into your pocket: replace the thermostat with the fancy 2-Stage one. It has a big (slow reacting, like all other thermostats as well as a tiny (fast reacting). It helps with a condition called temp gauge overshoot, and generally keeps the head temps more stable.

It's really easy. Just don't forget to order the gasket. And probably you will need some coolant. (Still recommended at this point: Toyota Red)
  • $35-$40 for a 2-stage thermostat, Toyota P/N: 90916-03070
  • The above pictured 2-stage unit was purchased 3/25/03, it was in stock at my local Toyota dealer
  • The stock is thermostat listed for my '85 22RE is #90916-03078 and is pictured in the right image (upper left corner)
  • Both are stamped 88C (190F)
  • Both the 070 and 078 thermostats are the same diameter, use the same o-ring gasket and have the little "jiggle" breather valve
https://www.4crawler.com/4x4/CheapTr...tml#Thermostat

Last edited by ev13wt; 03-18-2019 at 08:42 AM.
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Old 03-18-2019, 05:47 AM
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So basically I shouldnt worry about it then?

ev13wt, you mention the ECU coolant sensor, and right there I suspect something is going wrong, because even since repairing the engine recently (new gaskets too), the machanic couldnt figure out why when weather is colder (but not really cold, actually 50 degrees or less) the engine just cranks and its very hard to start. Thats why he put the cold start injector on a button on the dash so I should hold it while cranking to get it started. And thats why the whole thing with the temperature is smells fishy on my truck.

I read that there its possible on the 1st gen 4runner that the arrow is not moving beyong the middle of the Cold-Hot scale. Can this be happening to me to, on a second gen 3vze?

Yep, I know I am a bit parranoid, but after 1400 bucks for an engine repair 2 months ago I am pretty suspicios about stuff in the truck
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Old 03-18-2019, 08:43 AM
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These trucks have like 9 sensors or so. Test everything. All you need is a 29$ multimeter and proper instructions.

There are some great writeups. Start here:
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml
22-RE Temp senders (No idea about 3vze)
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Old 03-18-2019, 09:00 AM
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Originally Posted by Dilomski View Post
... the machanic couldnt figure out why when weather is colder (but not really cold, actually 50 degrees or less) the engine just cranks and its very hard to start. Thats why he put the cold start injector on a button on the dash so I should hold it while cranking to get it started. ...
I would be really surprised if your hard-starting was due to a thermostat problem. The Cold start injector timer does it's job when the coolant is dead-cold (air temperature). So the CSI system (most likely the timer) was not working when the air temperature was low.

Do you still have the timer? I would put my $6 multimeter https://www.harborfreight.com/7-func...ter-63604.html on the timer leads and try to figure that out. A push button is just a 1930s-era Pull-to-Choke; it's not doing your engine, wallet or the air we breathe any good.

($29 multimeter? I have more than one multimeter that costs even more than that, but I wouldn't bother using it on a car. Overkill.)
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Old 03-18-2019, 01:32 PM
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Ev13wt, there is no need to post 22R-E specific information if we are talking about the 3VZ-E engine as it can cause confusion.



What you are experiencing regarding the coolant temperature seems reasonable. I think your thermostat is fine.

The lower hose should be cooler than the top hose as the propose of the radiator is to radiate the heat from the coolant to the air and returns the cooler coolant to the engine.

Get rid of the "push button" for the Cold Start Injector, and lets put that system back to the way it was designed.

As Scope103 said, we can help you figure out what is at the root of your cold start problems through testing electrical components with a multimeter.


Last edited by old87yota; 03-19-2019 at 11:02 AM. Reason: Geezzz, I cannot seem to spell.......
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Old 03-19-2019, 07:08 AM
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Went to check the sensors, but unfornately its a PITA job. The only one, I got to touch was the coolant temp sensor, I guess, and couldnt measure it because wasnt prepared for it - couldnt reach it with my hands with all the hoses and stuff around. The only way to measure it is to stick it with longer wires and use aligator clamps. Have the clamps, but dont have the wires, gotta buy some. Anyway, here is a picture of the situation down there. Any info or advice is helpful. So far I managed to find info how to check the coolant temp sensor and the CSI time switch. No clue what the others are, or how to check them.

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Old 03-19-2019, 07:33 AM
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Here's my best pic:

Note that I have 4wd AND Automatic, so I get one more sensor.

In your photo, it looks like the sensors are slightly re-arranged. Get the wire colors; that will help you identify them.

It also looks like your ECT sensor is missing half of the connector body, FWIW.

I'm not sure how you identified your CSI timer. I don't see two wires; it looks like a vacuum line.
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Old 03-19-2019, 07:46 AM
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From what I read in the forum, they rearanged the places of the sensors from 1992 to 1995. I will check the colors of the wires. I used the FSM illustration to identify the CSI timer, but maybe I got it wrong - according to the manual it should be right next to the "U" shaped hose.
How do you manage to get there with your head, while the intake is on? I am not really a small guy, 6" tall, but still is very hard to see whats going on there
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Old 03-20-2019, 06:12 AM
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Ok, I dont want to open a new thread for this, so if you can give me an advice here?

My idle is running low when engine is warm. Around 500 rpm, and sometimes quickly dropping to 300 and turning the truck off. I drove it around 57 miles today, mostly outside of the city, but no highway (around 60 mph) and it used 18 mpg, which is actually propane-butane (truck can run on it and on gasoline), or how do you call it in the states, maybe natural gas? Anyway, it tends to use 1-2 liters more with this setup than gasoline, so fuel economy is good, very good. But the low idle is a PITA in city traffic. My mechanic fixed it 2 months ago, turning the distributor to 10 degrees, according to the manual. Maybe TPS sensor, throtlle body needs checking? Or VAFM?
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Old 03-20-2019, 06:21 AM
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propane-butane is called LP (Liquefied Petroleum) gas in the US. "Natural" gas is almost all methane, with a touch of ethane and a smidge of random stuff, like the mercaptans added to odorize it.

As to your question, I can't help.
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Old 03-20-2019, 06:23 AM
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Thanks, Scope. You are always helpful, as well as the other guys here. Will check the sensors too.
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Old 03-21-2019, 08:19 AM
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Cleaned the throttle body today, as well as the air intake hoses that lead to the AFM. Unfortunately, the hose which goes to the throttle body cut itself in two pieces It was already duck taped, now I just tore it apart. Took the battery off for a good 1 hour to forget the fuel calculations. Started it first time, disaster, barely kep it running with foot on the gas pedal. No wonder - a huge crack in the hose. Reducktaped it and this time around it ran better, still not perfect, but better. Only thing to do now is to order a new air intake hose, I guess. Does it matter if its OEM or aftermarket piece?
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