Workman

The thermostat went bad a couple days ago (stuck open). I replaced it with a new 180* thermostat and now it just won't heat up. Before the old one went bad, it would be completly warmed up in less than 5 miles. Now I can drive 20-25 minutes and the guage barely reaches the cold mark and the lower radiator hose will still be cold. Also, the heater still blows hot. I'll take any advice, it's annoying to think about how much gas is being wasted on the highway without overdrive.

Lumpy

Are you sure you burped the system correctly? You may have an air pocket in the system.

putneysmachine

Like Lumpy said, double and then triple check to make sure the is no air still in the system (3VZ's are notoriously tough to bleed).

If it was not a FACTORY TOYOTA thermostat, then I'd suspect that first. I've seen more (insert brand name here) thermostats fail right out of the box than I have seen them work properly. Aftermarket t-stats are made by diameter, not made by application. Junk, junk, junk. Spend the $20 for a OEM t-stat, they work.

BT

You can check your new T-stat if you take it out and put it in a pot of water on the stove and watch for it to open. But I would bet on air in the system.

vital22re

iTrader: (2)

air in the system, the coolant temp sensor is made to read water temp, not air temp.

Workman

Any good techniques on how to bleed it? Most vehicles seem to have their own method that works best. I pulled the thermostat back out after it didn't help and tested it in hot water. It opened around 185-190.

damienpottinger

just replaced cracked 3vze radiator, you've got classic air pockets tricking your tstat.

Workman

I did some searching for the best method of bleeding it but really couldn't find anything. When I did it, I just ran the motor with the radiator cap off and toppes off until it stopped bubbling. Ran it for about 30 minutes. But I know this method doesn't work on all cars. My Fiat Spider has about 10 steps to bleed the system.

sb5walker

Park on a steep hill with the front end high and the heater control all the way to hot. Remove the cap (obviously when cool enough) and run motor, adding coolant as needed.

If you hear gurgling or water flowing noises in the heater, you still have air in there.

Workman

I just used a funnel that screws onto the radiator to bleed out air. I've used them before and they work great. So now I'm pretty sure there's no more air. Hasn't changed a thing. A couple months ago I blew the lower radiator hose while driving out of state, I did a roadside fix and filled up with water to do another 2 hours of driving. I just topped off and ran it for a little while to bleed some air out and didn't have any problems from it then. It warmed up normally and didn't get hot and I really didn't have to work to get the air out of it. This time, it seems to bleed itself good, especially with the funnel aparitus I have.
So, I started thinking a little more into it than air pockets. Does the temp sending unit only send signal to the guage or does it also transmit to the ECU to tell the trans that it's warm enough to shift? And is there a way that I can test the temp sending unit? I've heard someone mention grounding it but I'm not sure exactly what to ground and how to tell if it works.

putneysmachine

There are 2 coolant temp sensors, one for the gauge and one for the ECU. Do a search for component location / wiring diagram..... but, I think the sensor for the gauge is at / near the t-stat and the ECU sensor is at the rear of the intake manifold (ya' know, the one that is a pain in the sack to get to...)

Like I'd mentioned before, if is an aftermarket t-stat, they are built to "fail" in the wide open state. If the coolant is constantly flowing past the t-stat, it's not spending enough time in the engine to warm up the coolant properly.

I hate to be a dead horse beater..... but a factory Toyota t-stat is always a win. It sounds like you have a handle on the air-bleed procedure.

sb5walker

Unless you elevate the front end and run the motor with heater temp control at hot and rad cap off, air remains trapped in the little upside-down U-shaped hose attached to the water outlet. That's the aluminum fitting bolted on the back of the intake manifold that contains 5 or 6 sensors. The air prevents coolant from flowing past the sensors, giving false readings.

There are two sensors that detect temp: the coolant temp gauge sender:


And the Engine Coolant Temp sensor which informs the computer that the engine has reached operating temp. The computer won't go into closed loop (using O2 sensor readings to calibrate mixture) until the ECT reports the engine at operating temp:

Workman

I should have mentioned earlier, a couple days ago I put a toyota thermostat in. Today, I pulled the front onto ramps, cranked the heat, and used the funnel bleeder. Didn't make a difference. I also grounded the wire for the temp sender and the guage only went to the cold mark and back down to below cold when I unplugged the ground. Shouldn't it have gone all the way to hot being grounded?
The wire I tested at was far left inline with the other sensors and senders at the back of the manifold and was the same as the first pic.

I may just replace both and see what happens. I hate throwing money at the problem and hoping it goes away but I'm out of ideas.

sb5walker

The odds of both the temp sender & ECT going bad at the same time is quite remote. Why not test the resistance of the ECT when motor is cold, and again when hot, and compare to the spec:
http://personal.utulsa.edu/~nathan-b...98engineco.pdf

That may at least tell you whether hot coolant is making it past the sensors. Then you'll have to see whether it's the temp gauge sender, the gauge, or wiring.

Workman

I'll give that a shot if I can find my multimeter. My only other thought would be that I may have something plugged up that's not allowing coolant to get to the sensors. It just seems like that would cause overheating. I have had a lot of issues trying to get all the rust cleaned out of the cooling system.

Workman

Just some new info. Today, after driving for about 30 minutes, I was adding some power steering fluid and I heard a gurgle from the overflow tank. I grabbed the upper radiator hose and it was hard from pressure. I released the pressure from the radiator cap and when I got back in and started it, the guage read right in the middle where it used to be. It stayed there at idle but dropped again when I drove it. After the drive, with the guage on cold again, I cracked the radiator cap loose to relieve pressure and the guage went back to the middle. To me, that's a good sign of air still in the system but how the hell will I get it out? Last time I bled it, I had the front on ramps, heater cranked, "bleeder funnel" attached and full, and I ran the engine at about 2k rpm for over an hour and the guage never got halfway. It also stopped bubbling up about 30 minutes into the bleeding process.

sb5walker

Sounds to me like you could have a blockage somewhere, either in a block/head passage, in one of the smaller diameter lines, or in the heater core. The burping technique you described sounds good & should have worked.

You might try flushing with a hose (you can get a plastic prestone flush kit for about 4 bucks) and flush several different lines, in several different directions. Backflush the heater core. Remove the block drain plugs and thermostat and go to town.

You might consider using a flush agent - something I usually never recommend because they strip the protective layer on the block and head, making them more prone to corrosion. But maybe it would help your motor. The safest effective ones are citric acid based - Gunk's 'SUPER RADIATOR FLUSH' is a good one.

If your coolant is fairly new, you can drain into a clean container and reuse.

Workman

I'll try one of those flush kits. A couple days ago, I decided to drain the radiator at the petcock so I could add some more antifreeze since I didn't get much in last time I tried. I used my same bleeding technique and now it seems to be much better. This morning was cold enough for frost on the windows but the guage almost made it halfway up during my 20 minute drive to work. Still wasn't far enough to get overdrive but that's progress to me. When I got home, I purged some air at the cap and I think I'll drive it tomorrow with the cap loosened to release pressure just to see if it will get some more air out. Hate to say it, but if I can't get the OD working soon, I'm gonna have to start driving my cavalier.

BT

When you grounded that wire, I would've expected the gauge to go full hot. How is the exhaust coming out of the tail pipe? I had a coolant sensor go out on a different car and it made it run really rich because the ecu thought the engine was freezing. I could see black all around the tailpipe and the bumper from the rich exhaust.

Those sensors are usually cheap.

It sounds like you've done a good job bleeding air. I've actually still got a little air in my system. Sometimes when I take a corner, I hear the gurgle of moving water. My gauge still reads fine though.

I would take a drive with the cap loose, the overflow full, and stop every few miles to top off. But it sounds as though you've already done a good job of bleeding. I would bet on a bad sensor.

Rice18

so far this thread seemed like the most helpful...
i have a very similar problem with my 89 3.0
early last winter i replaced the thermo sence then i have noticed a rushing water sound behind the center of the dash, i believe i have fixed that problem by burping the radiator... however the more important problem is that my temperature gauge does not register at all, once and i while it will pop back on and flicker maybe for 5 seconds but hardly ever.
at first i suspected wiring.... i was wondering how exactly i could test the connection with a multimeter and how to solve this problem.... sound like an improperly bled radiator to anyone??