1990 overdrive issue

[Taurus_Guy]

Hello People ..Im new and i have had my 4runner for almost 5 years now. Its a 1990 with 287,000 kms on it .. and recently i have had the motor replaced with a motor from a 92 that had about 150,000 when i got it and have put about 25,000kms on it since i had it put in. I have used this site to solve and diagnose many of my problems (GREAT SITE BTW!!!) .. but never signed up till now. i have had and solved every problem the 4runner can have up until this problem. My problem is this ... when i am driving in the city everything is good and i get overdrive no problem, but when i travel on the highway my temperature drops below normal operating temp and i loose overdrive. i have replaced my thermostat 2 times now .. and the second time i had toyota do it so they could do a coolant flush thinking that there may have been some build up preventing hte thermostat from closing. And now its still doing it. I read somewhere about some e-17 splice in the wiring that might fix it .. or mabey the temperature sensor but im not a mechanic. My truck has been problem after problem ... and i have spent too much money on it to sell it. Any suggestions would be much appreciated.

[Taurus_Guy]

Well all .. incase anyone has had this same issue ... i just got it figured out...

1. Replaced thermostat a third time (even tho i tested all 3 the third and second ones reacted the same so i prolly didnt have to replace it.)

2. unplugged and reinserted the e-17 splice right behind the steering pump (which apparently affects the overdrive if there is low resistance in that ground circuit.)

3. put 1 less litre of antifreeze back into radiator, ( so i think actually the radiator had too much coolant) took it for a run after doing all these down the highway and POOF the temperature gauge stayed at halfway and my overdrive worked again. YAY!! ...

[Brian R.]

Good job! I think you should replace the antifreeze you drained and keep the radiator full. Don't screw around with your cooling system. Removing some coolant from your radiator will only allow your engine to overheat if carried too far.

As you know, it is the thermostat that regulates maximum engine temperature, not coolant level. If the engine is running too cold, replacing the thermostat is the way to fix it - not draining coolant.

[Taurus_Guy]

So .. i am back to square 1 again .. that only helped for a bit so i put that fluid back in again .. and the problem is elsewhere. the next few things im gonna try are:

(1) replace the coolant temperature sensor, mabey its out of calibration.

(2) taking out the plastic connection and soldering in a wire for that e-17 ground splice behind the power steering pump. (which seems fine when ya look at it but i guess ya never know)

(3) replace my Rad cap

But a mechanic friend of mine had mentioned to me that it could be just coincidence that my temp drops and cuts out my overdrive on highway .. and that mabey the relay is shot for overdrive and when it heats up it cuts out. So he asked me to inquire about the location of the overdrive relay. If anyone can point me in the right direction to this device that would be much appreciated.

Also .. my truck only gets aprox 300kms, i have to fill up at about 280kms, to a tank of gas in the city. Its an automatic with v6 is this about right?? Anyways thanks in advance.

[Goatwater]

Might i suggest that you take a look at your Radiator Fan clutch. If this is seized. The fan will continue to turn rather than free wheel as the temperature drops when one gets on the freeway and the vehicle accelerates and sustains freeway speeds. You see there is temperature sensitive device on the fan hub which will cause the fan to free wheel (disengage) at cool temps. but as temps rise it will become viscous and turn the fan to draw air thru the Rad. Actually the bearing in the drive could be seized. To check your fan, turn engine off. Grasp the fan and try to turn it. If it does than the prob is elsewhere(your engine shoud be cool BTW) As you are there check for side play. Rock fan fore and aft. If it wobbles you are going to have problems down the line. The fan clutch is seperate from the fan so you can keep your fan and buy just the clutch alone. Hope this helps.

[Brian R.]

It's no coincidence. The ECM delays shifting into OD when the engine is not at operating temperature.

Originally Posted by Taurus_Guy

But a mechanic friend of mine had mentioned to me that it could be just coincidence that my temp drops and cuts out my overdrive on highway .. and that mabey the relay is shot for overdrive and when it heats up it cuts out. So he asked me to inquire about the location of the overdrive relay. If anyone can point me in the right direction to this device that would be much appreciated.