My 94 V6 is overheating. When started, the engine heats up to the midpoint very quickly (60-90 seconds). It idles at midpoint until the accelerator is pressed. The temp shoots up when the rpms rise and then drops back down when the accelerator is released.

I have replaced the thermostat, the temperature sender unit, and the radiator. The previous owner tells me he has replaced the water pump. I noticed a little corrosion around the radiator cap housing, but I replaced the coolant when I replaced the radiator and the problem is still happening.

Any suggestions? Help!

 

If you replaced the thermostat yourself it is possible that an air pocket behind the thermostat won't allow complete filling of the system with coolant. I've got the same year and model Camry. Engine overheated immediately.

Get the engine real warm. Turn off the engine. Carefully remove the radiator cap. If there are steam pockets in the engine, the filler spout will shoot up like a geyser. Carefully add coolant and repeat until you think the system is full. The coolant level should stabilize.

This is dangerous stuff, so stand back, wear gloves and a sweatshirt with long sleeves. Plenty of rags and towels. You can do this with the engine off, so long as you are sure that the thermostat is hot enough and completely open. Replace the cap and recheck your temperatures with engine running. My system took an additional half gallon of coolant with this method.

The level should stabilize, and if it doesn't, you have other problems.

 

Well, I let the engine heat up with the cap off and topped off the coolant as the air bubbles released. Put a full 2 gallons in. Capacity is 2.3 gallons, so the residual coolant left in the system after draining it would probably be about .3 gallons, don't you think?

 

When engine hot feel the upper and lower radiator hoses to determine if the one is hot and the other cold due to lack of circulation.

Engine cold squeeze the large radiator hoses to purge the air out, then add more coolant as required. When refilling there is always some air in the system. Ideally you want to be adding as much coolant as was drained out.

Did the previous owner imply the engine was overheating, the result being the water pump change?

Was the pump really changed? It is rare but happens that the water pump impeller fails due to corrosion, separates from the drive shaft, etc. the result is an overheating engine.

Have you checked for a failed head gasket, a block test can be conducted to check for exhaust gases in the coolant. Exhaust gases can cause the coolant temp to sky rocket and boil over.

Did you replace the sensor for the dash temp gauge or engine?

Have you checked the coolant temp with a thermometer to compare against the gauge indication?

If the engine temp is raising 30-90 seconds from cold start something is amiss. In a normal operating engine the thermostat would most likely not be opening yet and thus no coolant circulating. This would then eliminate the cooling system as a problem and point to a head gasket failure.

 

My mechanic did the block test and found no exhaust gases in the coolant. I replaced the gauge sensor. After replacing the radiator (which was definitely leaking), I bled the system a few separate times to ensure the air bubbles were all out. Also, after replacing the radiator, there are no other coolant leaks. I have not taken an actual thermometer to the engine block. I'm assuming a cooking thermometer would work, but where would I put it? And what's the proper operating range exactly?

After feeling the hoses, I think that coolant is not circulating. But the curious thing is that the heater works. It only blows hot after several minutes, like a normally operating heater, even though the temp gauge shoots to the midpoint in about 30 seconds. Perhaps because since the coolant is not moving in the water jacket, the heat emanates through the stagnant coolant and eventually reaches the fluid in the heater hoses...?

Since the cap is next to the engine block and not right on the radiator, it's difficult to visually check coolant flow, but with the cap off and the engine running there is absolutely no movement at all in the filler spout. Not a bubble or chug or anything. The previous owner allegedly replaced the water pump, but it seems to be the only thing left. This is a particularly compelling theory since the engine keeps at proper operating temp at idle and starts to overheat when the accelerator is applied, whether it is in drive or in park.

Unless, and it's a long shot, but could the replacement gauge be improperly calibrated? They're universal, aren't they? Guess I'll find out when I take a thermometer to it

Thanks in advance for the input. This is getting to be a real head scratcher.

 

A cooking thermometer will work fine Remove the radiator cap and place it in the filler port. Let the engine heat up while reading the temp.

The temp will raise until the radiator fans start up between 199F and 208F.

If the everything is working OK, the engine should be able to idle without over heating as the fans will draw in enough air.

The AutoZone websites vehicle repair guide section may have resistance info for checking the gauge temp sender. So much resistance for a certain coolant temp.

You might consider jury rigging the sender to allow emersion in hot water while still being hooked up to the cars electrical system. Have the water at 185-190F, determine what the dash gauge indicates. This will test if the gauge system is OK and the coolant is actually getting hot this quick.

The gauge sensor should be a standard part, no need for calibration.

When you put the thermostat in did it have a air bleed hole and if so was it place in the up position. And the spring system placed toward the head? The thermostat temp setting should be 180F.

Might remove the thermostat and determine if this changes anything with the coolant circulation.

The heater coolant circuit may bypass the thermostat.

 

On my '94 V-6 I can easily see the movement of water in the filler block with the cap off. I just give the throttle a bit of tweak.

On examination, the pump impeller was eroded away, but still moving a little water.My mechanic demonstrated the lack of flow to me before replacement. I could drive the car, but would have what we call in the aviation world, temperature excursions of the engine.

I'm no mechanic and wouldn't want to try the thermostat or pump replacement on my own. On the whole it seems that the Toyota engineers designed everything to last for 200,000 miles. Tolerances are kind of tight. That was their benchmark to make the Camry a head-to-head competitor with Mercedes cars.

 

Thanks for the info on that, bravozulu. That's an important detail to know. I want to get in there and get my hands dirty, but my mechanic says I should probably leave this one to him haha.

Toyomoho, you've been very helpful too. I think I've got this nailed down to the water pump. I'll let you know what happens

 

buddy, it's either leaking head gasket (yes, I know what your mech did) or "previous owner" is a darn lier and never touched that pump, passing issues onto you.
sellers are tellers, you know.