drguitarum2005

This has happened to me a couple of times, tonight being what prompted me to ask about it. I have a 2000 Tacoma 3.4 and tonight i was idling at a stoplight, with the defroster (and thus ac compressor) on, temperature at about half hot, half cold (defroster air temp), and i noticed that the air coming out was getting real cold, like no more heat. i switched it all the way over to hot and it barely got warm and i looked at my engine temp gauge and it was slowly rising. this has happened before (minus the compressor part because i've never had that on before when this happens) and it always goes away when i start moving again. when i start moving the engine temp goes back down and all function is normal again. what could it be?

dairyjato

check coolant level if it isnt low maybe thermostat.

cackalak han

Also, you might have some air in your system. I suggest replacing the thermostat and bleeding your system. Can you get any good heat coming out at all?

drguitarum2005

coolant level is good. i might try doing the thermostat. the thing that makes me think its not just the thermostat is that the heater stopped working right when it was doing that, so it seems like more of a mechanical issue than just a bad temperature reading. when its doing that, it was hard to get much hot air coming out. normall i have no problem getting hot air to come out.

warriors_03

confused, when you are idling and the temp gauge is rising, is it rising above normal (1/2 way up the guage) and then when you start going it is going back down to normal?

drguitarum2005

yes, its NORMALLY half way up the gauge but it rises past that (and up into the red, so that I get a CEL sometimes) when idling (when its doing what i said above) and then when i start moving again it goes back to normal (1.2 way up the gauge)

warriors_03

Sounds like a bad thermostat to me, but thats an educated guess at this point. Careful with it getting into the red, thats overheating and not good for 3.4's.

98runner210

you sit there and watch the gauge go into the red?! I'd shut down at 3/4! It's not giving a CEL cause the gauge is so high its giving that because the motor is so hot it is probably pinging or detonating like crazy. Might wanna look at head gaskets...

drguitarum2005

to clarify, its only done this twice. the first time i was sitting at a drive-thru window and i wasnt paying attention to my gauges and all of a sudden i see the CEL go on and my temp is in the red. i shut it down until i had to move and as soon as i start moving the temps went back down and a few miles later the cel went off and i never saw it again. that was back in november. a few days ago it STARTED rising in temp again but i started moving before it got to 3/4 and it went back down.

drguitarum2005

a little addendum here: last night it was kinda cold outside and i was in a place idling for a long time (from startup until the engine got warm). even when the engine got warm and the RPMs dropped (to 800, the typical operating RPMs) i could not get the heat to work. it blew cold until i manually (via the accelerator) held the engine RPMs at about 1200 for a few minutes. THEN it got warm and stayed warm.

what could that mean in conjunction with the rest of my stuff?

NicCantDecide

sounds like air in your lines. If you just let the engine idle at a specific RPM range, the air bubbles will all collect in a certain spot (different places depending on the design of the coolant passages). But once you start moving and revving the engine to different RPMs, the pressure changes because the water pump is spinning at different speeds and it gets it all moving again.

Start up your engine (when its cold) with the radiator cap off and watch the coolant flow through, if bubbles come up you had air in your lines. Letting it run with the cap off for a few minutes should get the air out of the lines along with some tapping of the upper radiator hose.

cackalak han

So did you replace the thermostat and bleed the system?

drguitarum2005

well, the funny thing about that is that i did that last weekend with the front end a foot or so higher than the rear end and nothing really happened. i didnt look directly into the radiator (i didnt want fluids shooting out at me) but i was able to watch just inside the top and nothing really happened...i didnt see fluid or anything, just the coils. my reservoir is mostly full and it didnt suck any in from that. this weekend ill probably top off the radiator through the cap and try again.

i did no replace the thermostat yet, i ran out of time, but thats on my list of things to do. i thought i would add the little bit of new information in case that changes anything

warriors_03

You should fill the radiator full. That will make sure it is full. The fluid in the resevoir won't get pulled in until the engine is really warm, and enough steam pressure is built up to overcome the pressure cap, or you are on a long trip and it can work for a few hours and help equalize all the pressures. I would fill the radiator full (almost up to the top of the upper part when cold) and then let it warm up and start sucking the stuff in and keep it full...this might take a few runs to get it done.

drguitarum2005

ill definitely do that on friday or saturday. am i to assume that all RED ethylene glycol anti-freeze is the same? i need to pick some up but i have no clue what type is in there right now, i think the dealership did it at 80k miles wen they did my timing belt and water pump

mastacox

Your radiator is probably way low! You should be full all the way to the radiator cap, and if it goes lower then it will pull fluid from the reservoir.

98runner210

If you are too low it may not suck it in from the overflow. My Maxima is like that, if it is too low it will not suck in from the overlow and the air in the system makes it purge more of the coolant out! When I replaced the thermostat on it, i made sure the radiator was full and got a good cap and have not had a problem since. (by the way different car but same symptoms)

mkgarrison5

why didnt you have the thermostat replaced when they did the tbelt and waterpump??? to me that would have made more sense.