1992 Toyota Corolla purging air after thermostat & hose

KEEPITRUNNIN

MEMBER
1992 TOYOTA COROLLA
4 CYL
FWD
AUTOMATIC
116,000 MILES

I replaced my thermostat (it was periodically sticking open) with a genuine Toyota stat & also replaced the lower hose. The new stat had 82 degrees C engraved (that's 189.6 F), same as the old one. When I tested the old stat, it opened at about 187 F but the new stat didn't open till about 197 F (it closed at 186 F). The instructions in Haynes for Corolla 84-92 says to run the engine (after refilling) with the radiator cap off, until the thermostat opens & coolant begins to flow thru radiator; then top it up & burp it by sqeezing the upper hose. Well, the thermostat won't open. The gauge on instr panel goes to midpoint; I don't know if that's high enough to open the new stat, but the old one kept it some cooler before it started acting up. I'm afraid air is trapped & not letting the coolant get to the stat. I've had trouble purging the system in the past after doing a radiator flush. I'm sure I got the stat in correctly, with the possible exception of the exact orientation of its bleed. I oriented it in the up position & didn't know to shoot for the 11:00 position that I see rec by "certified 2carpros tech" mmprince4000 in one of his answers on this site. What can I do? I'm afraid to drive the car any distance for fear of overheating it.

4 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Hi keepitrunnin,

Thank you for the donation.

Thermostats would work correctly only if it is completely immersed in coolant and if any air are trapped in the system, it might not be opening at the predetermined temperature.

Most temperature readings would register approximately 1/2 on the gauge if the AC is not used.

If too much air is trapped in the system, running the engine would result in coolant being pushed out of the radiator neck as the thermostat is not opening.

I would advise running the engine for 3 minutes, turning it off. Wait a few minutes and top up the coolant. Repeat the above process a few times till topping up is not required.

Close radiator cap and run engine till cooling fans comes on. When cooling fans stops, turn engine off.
Let engine cool off and remove radiator cap to top up coolant.

Start engine with radiator cap off and wait till the coolant starts to circulate, indicating the thermostat is opened. Top up coolant as required and bleeding should be complete.

During above process, remember to keep the heater working at maximum to allow the heater core to be bled as well.

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Thursday, January 14th, 2010 AT 7:09 AM

KEEPITRUNNIN

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2 POSTS

The advice given may be good but didn't really offer anything that I hadn't already tried. When I'd run it with cap off, even before writing for help, the level didn't drop, so I couldn't add more fluid. After repeating the following process (as well as some other things) several times, the problem persists: ran it with cap off for several minutes till temp reading peaked (about midpoint on gauge) & never saw any flow; made sure some fluid in overflow/expansion tank; turned off engine; tightened cap; let engine cool; observed some fluid sucked out of expansion tank 1st few times. Never feel any heat in lower hose from thermostat to bottom of radiator, even after driving it for several miles (temp gauge peaks at midpoint after less than a mile, even though it's fairly cold out here in Ohio. I do get good heat out of heater & my transmission is shifting okay now (that was my initial problem caused by the old thermostat being stuck open). Bottom line: I haven't been helped yet.

PS The answer I received included the line, "Most temperature readings would register approximately 1/2 on the gauge if the AC is not used". I don't know what it means by "most temperature readings".

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Saturday, January 16th, 2010 AT 7:44 PM

KHLOW2008

MECHANIC
41,814 POSTS

When fluid is being sucked out of expansion tank, it means air is trapped in the system and the cooling of the coolant in system would create a vacum to do that.

When the engine is cold, did you recheck the coolant level at the radiator cap?

There might not be any problem with the system now as you are gettin good heat from the heater and the temperature gauge is consistent.

The lower hose would not heat up if the coolant in the radiator is being cooled sufficiently fast before it is passed through the lower hose to the engine. Cold weather is as good as the cooling fans working to cool the radiator.

Under temperate weather conditions it would take the coolings fans to start operating with at least 20 minutes of running.

Did you try running the engine till the cooling fans comes ON?

Generally the temperature gauge would read at 1/2 on the gauge, that was what I meant.

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Sunday, January 17th, 2010 AT 12:32 AM

MMPRINCE4000

MECHANIC
8,548 POSTS

The thermostat has a small hole in the housing with a small pin in it, that pin must be at the 11:00 position. This bleeds air from head side into thermostat side.

Sounds like you followed the correct procedure, however you should see coolant flowing through radiator when thermostat opens. Also make sure you are using a 50/50 mixture of coolant and water, a higher mixture of coolant will affect the thermostat, since it is the water that transfers heat, not antifreeze.

Did you replace the thermostat seal when you installed it? The seal is a large O ring that fits around the thermostat, if leaking it will leak coolant around thermostat and cause it to not open, or take a long time to open.

I would try the procedure again, until coolant flows through the radiator, also quickly touch the lower hose to see if it is hot, if it is, then thermostat is open.

If you still have the problem, then remove thermostat and flush entire cooling system, you may have a blockage in cooling system.

If this is a 3 speed auto (A131L) the thermostat (or coolant temp) does not control shifting, the TV cable does, make sure it is adjusted correctly.

As KH mentioned, MAKE SURE the heater is set to max heat when filling.

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Sunday, January 17th, 2010 AT 7:26 AM