Help with coolant Temp switch - Toyota Nation Forum : Toyota Car and Truck Forums

ss1670 · 09-05-2007, 07:02 PM

I recently purchased a 1994 Camry with 5S-FE and an overheating problem. He replaced the radiator with an aftermarket. Still ran hot on him. A "mechanic" told him it was the head gasket. Long story. I bought the car as is.
The car had no signs of headgasket problem. No white smoke. No milky film in oil or oil filler cap. I did a compression check. All 4 cylinders peg at 175 psi.

I changed the thermostat to a factory Toyota thermostat and when I started to run the car with the new stat the temp gauge started to climb but I noticed the cooling fans did not kick on. Reading through Haynes manual, I unplugged the Coolant Temperature Switch/sensor from the bottom of the radiator and the both fans ran. They will run with the car started or with the key to the "on" position. Took the car out (about 5 mile drive) with the fans running and it pegged on the temp guage about half way up the whole time.

I thought .. aha .. the switch is bad. I assumed that with the fans running "unplugged form the switch" that the Fan Relay Number 1 and the Main Engine Relay must both be good and eliminated them as the culprits. I bought a new temp switch at the dealer ( $90 ) and installed it. Filled with coolant and started the car. Temp guage began to rise and still no cooling fans running. Not happy camper!

Is my thought process correct that the relays should be good considering the fans will run with the temp switch unplugged or do I need to be looking at them?
Any suggestions on what my next steps should be?

Thanks!

95PimpingCamry · 09-05-2007, 07:17 PM

Your right, it does sound like the relays are good. But I know that there is also a temp sensor just to the right of the engine head on the part that connects to the upper radiator hose. You might want to have that checked/replaced. It is possible that if that temp sensor is bad that your temp gauge will tell you that the car is over heating when in reality it is not.

ss1670 · 09-05-2007, 07:27 PM

95PimpingCamry - I was thinking that the sensor I replaced is really a "switch" to activate the fans while the sensor you allude to is probably the traditional sensing unit that is connected to the temperature guage itself and doesn't have anything to do with activating the fans. Is that the case? I need to do some more research and really wanted to elimate having to test the relays if they're not the culprits here.

95PimpingCamry · 09-05-2007, 07:36 PM

I believe your correct ( I don't know for sure, so don't hold me to it) that the one you replaced acts as a switch and the one that I mentioned is a traditional sending unit. What I was thinking was that your not over heating at all. I was thinking that the sending unit is faulty and telling you that your engine is hotter than it really is. If this is so that would mean that your fans aren't kicking on because the engine is not hot enough to need the fans.
The Haynes manuel tells you how to check the sending unit on page 6-8. Hope this helps.

Stillrunning · 09-05-2007, 07:58 PM

You should have three switches on the upper rad hose manifold at the head; a temp gauge sender with one wire, an engine temp sensor with two wires for the ECM, and an engine temp vacuum switching valve (VSV) with two hoses to it. The engine coolant temp switch (ECT) on the bottom of the rad turns the fan off/on. Your gauge seems to be operating OK from your description. I'm wondering if the ECT switch has coolant going to it? If you unscrew it till the o-ring comes off its seat can you get coolant coming out the rad? If you still have the old switch you can test it with hot water and an ohm meter to see if it worked OK. I can provide you with specs if you want.

Stillrunning · 09-05-2007, 09:07 PM

I've been giving this more thought. What if the ECT switch is ok and the coolant never gets above the set point on the switch to start the fan because the rad is cooling it properly. Then as the coolant goes through the engine and head it heats more than what it should because you do have a problem with the head. That would cause the temp gauge to show higher while not tripping the fan because the two temp sensors are in different locations. When you run the fans full time with the ECT disconnected you actually over cool the coolant so that it then enters the engine below what it normally should. That would then compensate for the overheating head - maybe, and give you the lower temp on the gauge. My fans don't run when I'm in motion, only when idling as there is enough air flow through the rad when moving.

dc_98_cam · 09-05-2007, 09:45 PM

Quote:

Originally Posted by ss1670

95PimpingCamry - I was thinking that the sensor I replaced is really a "switch" to activate the fans while the sensor you allude to is probably the traditional sensing unit that is connected to the temperature guage itself and doesn't have anything to do with activating the fans. Is that the case? I need to do some more research and really wanted to elimate having to test the relays if they're not the culprits here.

Water Temp Sender ... single yellow wire with green stripe.
Only goes to combination meter on dash .... does not connect to fan activation logic.
...Maybe replace this and see where you are at.

ss1670 · 09-06-2007, 08:50 AM

I will do some additional diagostic testing on the fan activation circuits based on Haynes info. I did order a new radiator. The previous owner did replace it but then took it to a "mechanic". He mentioned that they pressure tested the system and he had to "re clamp" the bottom of the radiator at the plastic tank afterwards. While I don't see any leaks, I am suspect that there may still be issues with it and the system is not fully pressurized with the cap on. I will replace it this weekend and test the fan circuitry.

ss1670 · 09-06-2007, 07:25 PM

One additional piece of info. This evening, I started the car and turned the A/C on. Both fans activated and ran. I let the car idle for about 10 minutes and it never overheated but you could hear and see the fans cycle on to a higher RPM then cycle back down to a normal speed. Doesn't that point to no problems in the circuitry?

dc_98_cam · 09-06-2007, 08:37 PM

The wiring diagram doesn't provide much detail with regard to the operation of the fans. The description merely says that if there is a problem someplace, a check engine code will be recorded in memory ... to be read and interpreted.

There is one coolant sensor that provides an input signal to the engine. A malfunction of this component would seem to be included in the CEL codes.

If you can't actually prove that the engine is overheating ... nothing obviously wrong ... other than the instrument panel gauge, then assume that the system is working properly.

Stillrunning · 09-06-2007, 08:43 PM

The manual calls the PS fan the A/C condenser cooling fan and the DS fan the electric cooling fan. On activation of the A/C both fans operate and I would think that separate relays actuate the fans for A/C and cooling. If you turn off the A/C the fans should stop and when the coolant temp reaches set point the fan/fans turn on. I don't think these fans are two speed, they're either off or on, unless only one operates for coolant cooling and both operate for A/C. If you turn off the A/C and disconnect the ECT switch connector the fan/fans should also operate. This will tell you that the relays are OK. You still haven't proven the ECT switch, although it is new so it should be OK.

ss1670 · 09-13-2007, 02:03 PM

UPDATE: think I discovered the problem. Sorry for the long post!
I ran Prestone flush in system the other day. Today I flushed the system with garden hose. I removed thermostat and replaced the housing. I disconnected both radiator hoses from radiator and ran water through the hose connected to the thermostat housing. I let the car idle the whole time. No major debris or gunk evident. Put back in the new Toyota OEM thermostat.
I changed out the radiator with a new one. Filled with Toyota Red and distilled water. Ran the car at idle. As the temp gauge inched over the middle point and continued to rise the fans still DID NOT kick on. The radiator cap was open the whole time and now I see steam billowing out of the cap opening. I shut it down.
Here's a couple observations why I think it may be a water pump issue.
1. Top of radiator was hot to the touch. The bottom of the radiator was cool to the touch. Probably explains why the Coolant Temperature Switch is not activating.
2. The bottom radiator hose to the thermostat was barely warm as if the hot water in the block was just backflowing through the thermostat. Top hose was hot to the touch.
3. I never noticed any gushing in the radiator when it was running. With a properly functioning water pump, shouldn't one see a lot of turbulence in the top of the radiator?

I had the heater on the whole time and it never blew hot air. With what I've seen doesn't it make sense that maybe the pump is bad? The steam I saw and the top hose being hot might mean that the water in the block is boiling and letting off steam passively to the radiator.

I will probably tear it down to inspect and replace the water pump if necessary as it's a lot easier than tearing into the head gasket at this time. Any thoughts on other ways to diagnose the water pump? Thanks in advance.

dc_98_cam · 09-13-2007, 02:27 PM

Examine the leakage hole on the water pump for precipitate .... indicates failure of pump shaft seal.

ss1670 · 09-13-2007, 02:53 PM

dc_98_cam - is it possible to pull off some of the timing belt covers to inspect without having to rip it down to everything?

Stillrunning · 09-13-2007, 03:14 PM

ss1670, you don't know the thermostat is not stuck closed, even though it's new. That would not allow flow. You could just remove the thermostat and run it without one to test flow or you could place it in some hot water and watch it open - or not. I think if the WP shaft seal was leaking you'd see coolant coming out the drain hole of the bottom TB cover. The WP should still flow even if the shaft is leaking. Other possibilities could be impeller shaft is sheared or impellers corroded so much they don't move coolant or TB has slipped off WP sprocket or TB was installed incorrectly and is rotating WP backwards all of which I doubt. You can just remove TB covers to inspect WP drive sprocket. From your description it sounds like the water in the rad is not reaching fan switch set point.