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#1 Old 03-24-2008, 09:47 PM
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Camry overheating

Symptoms: car temp gauge creeps all the way into the red in all city or freeway driving. Takes three or four minutes of driving to get the temp gauge to the red.

The coolant temp gauge on the driver's side was replaced. Engine didn't appear to have overheating issues with the old sensor (now broken).

Radiator is original as far as I know. The upper and lower radiator hoses were replaced as well as the thermostat. The water pump is new.

The fans do not turn on at any time. If you unplug the temp sensor on the passenger side door with the key in the ON position, the fans spin correctly. Driving around with the fans turned on manually (sensor unplugged) doesn't prevent overheating.

My current thoughts: new temp sensor is bad and the engine really isn't that hot or my radiator is clogged. Any other thoughts?

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#2 Old 03-25-2008, 12:12 AM
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When the temp gauge goes up does turning the heater to full hot and the fan to high lower the temp indication? How is the temp at idle? If engine heats up at hwy speeds suggests lack of cooling.

Can also remove radiator cap, install a thermometer and let the engine heat up. The radiator fans should come on at around 194-199F. When fans are on compare with temp gauge reading.
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#3 Old 03-25-2008, 12:31 AM
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Originally Posted by toyomoho View Post
When the temp gauge goes up does turning the heater to full hot and the fan to high lower the temp indication? How is the temp at idle? If engine heats up at hwy speeds suggests lack of cooling.

Can also remove radiator cap, install a thermometer and let the engine heat up. The radiator fans should come on at around 194-199F. When fans are on compare with temp gauge reading.
Turning the heat on lowers the temp a little bit, but then it creeps back up. At idle the temps sometimes lower back down to about 3/4 up, but then make their way back to up the red or just under. It shows the same symptoms with city driving and highway speeds.

I need to get a disposable temp gauge to see what the radiator is doing, but I haven't heard or seen the fans come on of their own accord.

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#4 Old 03-25-2008, 12:03 PM
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Another thought: I do not have the plastic splash plates reinstalled on the car yet. This may cause airflow to not travel through the A/C condenser then the radiator. I'll slap them back on and take a test drive to determine if it's the issue.

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#5 Old 03-25-2008, 12:06 PM
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I see that you replaced the thermostat. However, it sure sounds like a T-stat problem. When it was replace there may have been an air bubble that didn't get bled out ( I think the Toyota t-stats have a small hole at the top to allow air to pass. The aftermarkets may not.). Often, you can park the car on a pretty steep incline and it will allow the bubble to escape. Also, if that doesn't work, would it be possible to pull the t-stat out and run the car to see if it still gets hot? If it doesn't get hot then it's either a bad t-stat or one that was improperly installed.

You say: "The fans do not turn on at any time. If you unplug the temp sensor on the passenger side door with the key in the ON position, the fans spin correctly. Driving around with the fans turned on manually (sensor unplugged) doesn't prevent overheating." My recollection is that when the coolant is hot the sensor is open (no current passes through) and when it is cold the sensor is closed (no current). When you unplug the sensor the fan "sees" no current and turns on. Test the radiator temp sensor (even if new) to make sure that it is working correctly. If it is OK then it sounds like you have a short in the system.

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Often, it's the loose screw between the steering wheel and the driver's seat that needs to be fixed first!

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#6 Old 03-25-2008, 02:58 PM
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Since running the fans manually doesn't drop the engine temp, I am led to believe that is not the problem with overheating, but a side issue I need to tackle.

Another possibility I came across was the transmission cooler running very hot, due to a dying transmission. With this new information I have a plan of attack:

1. Make sure all grounding wires are installed correctly
2. Reinstall splash plates
3. Drive, check tranny coolant lines
4. Lines not hot: drain and flush system. Lines hot: cry (dead tranny?)
5. Remove tstat.
6. Still overheating: replace radiator
7. Not overheating: replace tstat

I'm getting tired of wrenching on this silly car.

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#7 Old 03-25-2008, 03:34 PM
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i would watch for the air bubble too. its a pretty common problem even with mechanics. just warm it, cool it , and warm it.. cool it. for about 10-15 times, it'll get rid of the bubbles
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#8 Old 03-25-2008, 05:54 PM
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I tried burping the system again, then let it run up to above normal operating temp. The upper radiator hose was almost too hot to keep a hand on and the lower was maybe a little bit warm - hard to tell! I replaced the radiator cap and let the car run for a few minutes, then checked the radiator hoses again: the upper was still very hot and the lower hose hadn't noticeably increased in temperature.

This sounds like a bum tstat to me, but wait, there's more!

I put the car into drive and the RPMs dropped. As it did this, you could watch the temp gauge plummet from just under red to the middle of the gauge. I put it back in park and it went right back up to red. It appears the lower the RPMs, the cooler the engine runs. It does the same thing when you place a load on the alternator by turning on the lights, fans, etc...

Off to drain the coolant and test the new thermostat.

(edit) Tstat tested ok. Now I am confused.

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Last edited by Skiermang; 03-25-2008 at 06:20 PM.
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#9 Old 03-25-2008, 08:54 PM
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This is screaming "electrical issue" to me. The under hood temps aren't nearly what I would expect with the needle just shy of red on the temp gauge. I can cause the needle to sweep a full 1/2 of the gauge down by turning on my highbeams, blower fans on high and trying to roll up all the power windows at once.

There's gotta be something amiss with my electrical system. A poor ground somewhere, perhaps?

(edit) What's "normal" operating temp for comparison when I get my hands on a non-contact thermometer later tonight? The valve cover, cylinder head, etc... Thanks!

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#10 Old 03-26-2008, 09:04 AM
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The resistance in the sending unit input to the temp.gage is getting DOWN as the car heas upyou may have to disconnect the wire from the tem. sender unit on the engine when it warm and off , turn ign on and verify that the needle at the very buttom.
The second thought is to measure the alternator voltage at 1500 rpm,making sure it not 15+ volts(sign of filing regulator or failure in stator feedbac circuit.
If the radiator core is cool while the upper hose is hot suggests bocked tubes.
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#11 Old 03-26-2008, 10:09 AM
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The resistance in the sending unit input to the temp.gage is getting DOWN as the car heas upyou may have to disconnect the wire from the tem. sender unit on the engine when it warm and off , turn ign on and verify that the needle at the very buttom.
The second thought is to measure the alternator voltage at 1500 rpm,making sure it not 15+ volts(sign of filing regulator or failure in stator feedbac circuit.
If the radiator core is cool while the upper hose is hot suggests bocked tubes.

If we assume the temperature sender is at a constant resistance and we lower the voltage by putting a load on the alternator, the current running through the gauge would drop, causing it to read lower. That's my line of thinking, please correct me if I missed something.

The alternator passed the testing in the charging section of the service manual. It was just under 15 volts according to my analog multi-meter. I'll check it again with a digital multimeter from a buddy though.

Here's a quick diagram of the radiator:


From what I could tell, the bottom radiator cap was a constant temperature. This rules out partially clogged coolant tubes, right?

Yesterday I flushed the radiator with the garden hose after draining it. I backflushed it by putting the hose into the lower radiator hose, then back to the top, then the lower, etc... until it ran clean.

Also, after letting the car get to the "red" on the temp gauge and dropping it down by putting an electrical load on it, I felt the lower radiator hose warm up. It seems the temp gauge is reading really high so I am stopping the motor before the thermostat opens.

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#12 Old 03-26-2008, 10:56 AM
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The engine temp. sending unit (in the engine), NOT THE GAGE on THE DASH has high resistance when engine is cold, and low tesistance as it warms up.
I hate to ask, if there is any blockage in the upper hose outlet-to-head flange that causes flow restriction? (Mispositioned gasket) almost impossible to imagine!
Is the water pump impeller clean?
I "authopsied" 79 supra 10 years ago on the junk yard, the pump impeller turned into the rusted blob, spinning, but not pumping.

Last edited by Doctor J; 03-26-2008 at 10:58 AM.
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#13 Old 03-26-2008, 11:23 AM
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Originally Posted by Doctor J View Post
The engine temp. sending unit (in the engine), NOT THE GAGE on THE DASH has high resistance when engine is cold, and low tesistance as it warms up.
I hate to ask, if there is any blockage in the upper hose outlet-to-head flange that causes flow restriction? (Mispositioned gasket) almost impossible to imagine!
Is the water pump impeller clean?
I "authopsied" 79 supra 10 years ago on the junk yard, the pump impeller turned into the rusted blob, spinning, but not pumping.

So the temp gauge in the dash doesn't read amperage? How does it display change in the sensor's resistance? I want to make sure we're on the same page.

I didn't see any blockage on the upper radiator hose outlet area. The gasket was installed correctly and didn't cover up any of the flow area.

Impellers are clean: I had run my finger over a couple of them when the thermostat was out last. The water pump has all of 10 or 15 miles on it, it was replaced when I tore down my new-to-me motor.

I will be testing the temp gauge and wiring by disconnecting the temp sender and grounding it, making sure the gauge reads hot, then putting a 150 Ohm resister between the wire and ground to verify it reads "normal" operating temp. Page 39 of Body Electrical gives a chart of sender gauge resistance.

Assuming the wiring and gauge pass this test I'll replace the temp sending unit with a new OEM jobber.

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#14 Old 03-26-2008, 03:28 PM
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It might be easy to pull the t-stat out and buckle it back up without the t-stat to just eliminate that possibility. Run it on a steep incline or hop a curb to help burp any air out of the system. But it would sure be nice to eliminate all consideration of the t-stat and it really shouldn't take too much time.

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#15 Old 03-26-2008, 08:27 PM
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Here's the latest:

When the temp sensor shows just shy of the red mark, the coolant at the top of the radiator is 170* F. The water outlet, where the top radiator hose meets the engine, has a surface temp of 188* F. At these temps, the coolant sender has 65 Ohms resistance. That appears to be about in spec according to the section on the sensor in Body Electrical.

The coolant switch still had continuity with ground despite the body having a temperature of 190* F.

I measured the top and bottom radiator hoses: the top was at 155 surface temp and the bottom at 144. For reference I started up my Civic, got it up to temp and measured its hoses: they were 80 degrees apart in temperature! It sure seems the radiator is at fault in this case.

I'll pull the tstat and try running without that later tonight and report back.

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