I'm trying to figure out why my engine temp is always very low. I do know for a fact that my gauges work. My car is a 4-afe toyota with a stock radiator and a modified fan. I also installed 2 additional fans which makes my fans equal to 3. I did it because during the summer months(I live in a tropical country.) I always drive in the city which is why I haven't noticed it until recently. I drove 300km trip with mostly freeways, and I noticed that my temp gauge is very low, which is why I could'nt push my transmission(I'm using an automatic with overdrive) to overdrive. I tried switching off all of my fans(I had a switch built so I could control which fans would run) but it would still go very low. What can I do to raise the temp to the optimal level without me removing the 2 additional fans? I can't push past 90kph because my transmission does not allow me(too cold temp for the overdrive to engage). I'm already on full load and I am revving hard just so I could increase my temp to no avail.

I really need the additional fans because when I drive in the city during summer, my temp goes very high, almost near overheating which is why I need them.


Additional details for my car: 95 Corolla A245e transmission My car is running on water as the coolant. I had the car serviced a couple of weeks ago,before the trip and they said everything was fine. I also had my radiator cleaned.
Temperatures in our country goes as high as 50 degrees Celsius especially during the afternoon in summer. However when I used my car that day it was not really hot, plus it was rained a bit when I was on the freeway. I have the standard temp gauge but I have no indication how cold/hot my temp(exact degrees) was. I did have a transmission replacement almost a year ago due to the mileage.

  • 1
    You may be able to attain a higher temp rated thermostat if the one you have is not stuck open In the first place (if there is even one in it). Aug 22, 2014 at 1:56

4 Answers 4


Get rid of the extra fans. If you're having to run fans constantly to keep the engine at the right temperature in the city, then all you're doing is masking another issue.

You probably have several other issues. The engine temperature and the transmission going being able to shift into overdrive should be independent. It seems like you are conflating two separate problems to be the same.

Find the actual cooling issues and fix them. Find the actual issue with the transmission, and fix it.

If you only have water in the system, that is a problem. It will boil and if you're using tap water, it will cause internal corrosion. The boiling and corrosion can cause damage and overheating. You should flush the cooling system and refill with the manufacturer-required coolant, typically a 50/50 mix of antifreeze and distilled water. If corrosion did occur, it my have caused the thermostat to stick open. That could cause problems as it will prevent proper pressurization of the system, and allow coolant to flow freely when it shouldn't be.


Replace the thermostat for sure, and while you're at it, replace the straight water with 50/50 antifreeze/coolant mix. Use the aftermarket fans ONLY during stop & go traffic in the city; on the open road they serve no purpose at all (ordinary wind from highway speed cools the radiator sufficiently in almost all cases). There's no need to remove the fans, just switch them off at any speeds above about 50kph - at that speed they're nothing but little windmills.


I agree with the suggestion to fix the underlying cooling problem. Your vehicle should be able to handle tropical temperatures, even in slow traffic.

I also agree with running antifreeze for the anti-corrosion and anti-boil properties. However, until you get the base problem figured out, you could continue to run plain water, as you may be having to do some work which would involve draining the cooling system. It will be cheaper (and better for the environment) if you are only draining water.


Instead of having 3 fans for city driving, I suggest rather installing a cooler-running thermostat and removing the two aftermarket fans.

What this will achieve is that in stop-go traffic, your one radiator fan will kick in sooner, keeping your engine at optimum temperature while still allowing the transmission to warm up enough to allow engaging overdrive.

Get a thermostat that opens 10 degrees celsius sooner, or at minimum 5 degrees. And as mr. TDHofstetter suggests, remove some water and add more anti-freeze. It will increase the boiling point of your coolant, making it more efficient at high temperatures.

  • The thermostat does not regulate when the fan turns on. Either a fan switch (which is thermostatic) will, or the ECM will control it based on the coolant temp sensor value. A lower temp thermostat will actually make it take longer for the fan to come on, as it will take longer for the engine to reach optimal operating temperature.
    – dobey
    Aug 22, 2014 at 13:12
  • I didn't know that. I thought the thermostat regulated the fan too. Thanks. Aug 22, 2014 at 13:20

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