Engine and Coolant Temp issue

[Vios-GT_07]

hi

just recently i've replaced my radiator, the old one was for the wrong car had dodgy cores and finally cracked the top tank.

Now, i've got a brand spanking new radiator, with the correct top tank where the coolant comes in from the side instead from the front. I'd say it definitely flows a lot better now..

Problem is, the car never ever warms up anymore.. the moment it gets up to normal warm temperature (92 degrees or so), and i drive it, the coolant temperature just drops.. on the freeway for 5 minutes and the temperate will drop right down to the end.. this plays havoc on the cold-start and brings the idle up to 2500 rpms + heater is cold + mis-fire under load because the air fuel mix is so bad, when the engine thinks it's in sub-zero conditions

I've replaced the thermostat thinking it was stuck open, was an 82 degree one, same thing happened, so i replaced it with the next one up, that's 91 degrees, and that helped a little.. it warms up faster, and the temperature doesn't drop until halfway, but it still causes high idle + bad air fuel mixture, and the car misfires under higher loads.

Is there anything i can do to maintain normal operating temperature? it's really annoying when that happens and i lose throttle response among other things..

[Javal]

Sounds like your problem has nothing to do with your new radiator.

AFM Maybe? Symptoms (high idle, poor air/fuel mixture) seem consistent with a busted one.

[Gavatron]

My MAP AE82 used to do this when I first got it. High speed on the freeway and the temp would drop right off and the high idle would kick in. I just used a higher temp thermostat and it fixed it for majority of situations. Still used to do it on long downhill stretches with no throttle.

[off-road]

Maybe water is bypassing the thermostat through heater lines or something.Do you have bleed lines in the coolling system that are too large.

[Kyosho]

Have you checked that it just isn't the water temp sensor playing up?
Fan stuck on 24/7?

[Vios-GT_07]

nope

the fan sensor is fine.. i have to idle the car for about 15 minutes before the fan kicks on .. yea that's how long it takes to get to the temperature where the fan kicks on.. then the fan stays on for 20 seconds before turning off coz that's how long it takes to get to the temp where it turns off.. fan is fine, sensor is fine.. water temp sensor is fine..

i've also bled the system, twice now.. this only stops the idle from fluctuating and "coughing" suddenly..

all heater hoses and lines are the correct size..

and yea after using the higher rating thermostat, i've noticed two things
1. it warms up faster now, and stays at a higher temp (the minimum at cruising is halfway betweem warm and cold)..

2. after cruising, it doesn't idle over 2000 rpms like with the 82 deg thermostat, and comes down to 900 rpms faster, less than 1 minute..

and yea fuel consumption is closer to normal now with the higher thermostat and i've eliminated the misfire coz of the odd mixture.. but i still want a more effective way of regulating the coolant temperature as even with the higher thermostat, it still gets too cold for my liking.. (too cold meaning cold enough to trigger the cold-start and start the stupid air fuel mixtures and kill throttle response)

[celicaboy_2000]

Some cars have a twin water temp sensor. One to control the fan the other for the ecu. Maybe the temp sender for the fan is ok but the other isn't? Also could be a loose wire on the temp sensor?

Matt

[Vios-GT_07]

temperature sensor that controls the fan is fine.. it's resistance based.. (like the coolant temp gauge's sensor)

the other two temperature sensors that goes to the ecu are working fine as well.. the ecu is getting correct figures about coolant temperature. diagnostics have proven that + aftermarket temperature gauge

the problem is i can't get the coolant temperature to stay warm.. when i start cruising, water temperature drops enough to trigger the cold start, high idle + bad air fuel mix ..

[celicaboy_2000]

I got no idea it sort of leads towards a bad thermostate but as you have mentioned you have replaced it... Also the idle up usually cuts off/on about 65-70deg which means the sensors are picking up that temp from the water, doesn't make sense.

Matt

[Vios-GT_07]

the standard replacement thermostat opens up at 82 degrees..

idle up + cold start slows down when temperature gets to about 80 degrees.. is fully disengaged at 85 degrees and beyond.. so when water temp gets back to 85 degrees adn below, the idle is increased slightly..

with an 82 degree thermostat, when cruising at nights, the temperature will drop from 87 degrees right till 60 degrees, and on a very cold night, till 45 degrees.. hence, full idle up cold start power..

[celicaboy_2000]

Have you modified the postion of the temp senders? What about the aftermarket sensor is it before or after the thermostate?

Matt

[Vios-GT_07]

nope everything is stock..

with the old radiator it was okay.. 82 degree thermostat, it would hold temperature very well... new radiator and this happens..

aftermarket sensor sits on the return hose, same line as the factory temperature gauge sender.

[Kyosho]

Is the radiator that's in the car DEFINETELY the correct one for your car?

Also, a strange one, but have you checked your base ignition timing?

[Vios-GT_07]

yeap it's definitely correct..

i've got the wrong radiator support for it too.. argh!! it had an AE-82 radiator and ae-82 radiator support for it... the top bracket is in the wrong place, but yea otherwise it's right.. the ae-82 radiator in there before worked well until i discovered it cracked..

and yea the base timing is correct, 10 degrees.. but i will get it checked out again tomorrow to be sure

[Dale]

The problem has to be thermostat or plumbing based, it shouldn't matter how cold the water is in the radiator.. the thermostat is meant to regulate the flow and keep the engine at the temperature it's rated at, it mustn't be doing that properly if it's getting too cold, cold water is coming in when it shouldn't be