Hi everyone, nice to meet you.

1994 Toyota Camry 2.2L, 257k miles
Symptoms:
Car overheats
Top radiator hose hot, bottom cold
Very shortly after take off the car begins to climb the temperature ladder
Not a lot of white smoke form tailpipe
Rough idle at first start, fine thereafter
No loss of coolant
No milky oil


What I have replaced/tested:
New thermostat
4 month old radiator
Visibly inspected water pump (went ahead and changed timing belt) no issues, turns freely
Replaced cam and crankshaft seals, no more oil leaks (would have to put in a quart every 70 miles or so. Sometimes sooner and that's when I realize I have had dangerously low oil while operating the vehicle but I consistently check the level because of the oil leak...I guess sometimes the leak is faster than my checks)
Both radiator hoses show no blockage
Flushed radiator
Replaced engine temperature control sensor
Replaced temperature sender sensor

So with all of this....the temperature still begins to rise when engine is under load. The fans do not kick on, I'm assuming it's because the fan temperature sensor is not receiving any hot coolant because the lower hose is cold. I disconnected the sensor so now the fans run constantly. I picked up a head gasket leak tester...within a few minutes the blue liquid turned green/yellow BUT I DO NOT SHOW THE CLASSIC SYMPTOMS OF HEAD GASKET PROBLEMS! Not much white smoke (normal for 257k miles), no coolant leakage and no strange noises or power issues. Then I had the idea to take the thermostat out and see what happens. Now the temperature never rises to mid level and the car at least gets me around town when I need to get somewhere. Both radiator hoses are warmish now too. I work from home so it's not a huge deal plus I plan on ditching the car anyway when I find the "deal." BUT I have an obsessive personality and I would like to at least solve this conundrum just in case someone else has the same problem and I can offer some sage advice. Obviously I have terrible gas mileage because the engine never heats up. A couple of other strange things. I know I will "burn" coolant but even after the car sits overnight I go to check the radiator cap and I can hear a pssssshhhhhhh and a slight amount of pressure when I take it off. Also, around the time the engine begins to creep to mid level (an indication my coolant/water is evaporating) I can see the overflow tank is completely full or overflowing. I drain that fluid and put back into the radiator then the car is fine for an hour of operation or about 40 miles before I. I can't see why it would be a faulty cap because of the release of pressure each time it's opened. I make sure to "burp" the system when adding coolant.

So for my questions:
Is there something I am overlooking?
Why won't the radiator pull from an overflow tank that is at mid level every morning and overflowing after driving? Especially if the seal/pressure seems to be persistent.
Would Blue Devil or another gasket sealer work for a short period of time?
Is there a blockage I'm not considering?
I know I should have some sort of gasket issues at 257k but is it really the gasket and nothing else?

 

Nice write up of your issue, very complete and you have definitely done some work. I really think your problem is a blown head gasket. You say not much white smoke? Well, that is a matter of interpretation. There shouldn't be any white smoke out of the tail pipe after car is warm enough to cook out the moisture built up in the exhaust system from sitting overnight. I had a Datsun 280ZX with a blown head gasket that did not spew white smoke at all but the over flow tank would over flow and spew coolant. The blown head gasket in my case was actually pressurizing the coolant system. On the piston's up stroke, air would be forced past the blown head gasket into the coolant system and the air would displace coolant. Hence, causing the over flow tank to over flow. The pressurized air into the coolant system could be enough to keep coolant from circulating around the engine block with the thermostat in place. With the thermostat out, the coolant is constantly circulated by the water pump and is enough to overcome the air being forced in.
All that being said, let's start simple. Make sure the thermostat is installed correctly, they are directional in some cases and being installed facing the wrong direction can hinder the opening and closing. Next, pressure test your cylinders. With a pressure test you will know if there is blown head gasket. It doesn't take much over heating to blow a head gasket. When you inspected the water pump did you actually remove it and inspect the blades of the pump? Sometimes the blades on the pump deteriorate over time and do not move coolant.
I seriously think that you have a blown head gasket and air is the obstruction that is keeping the coolant from circulating through the system as it should. Do the testing first to be sure. And keep us posted with what you find out.

 

Is there a way I could "rank" the possible effectiveness of a head gasket sealer before I do it by checking anything (glove test, etc)? What if I replaced the gasket without having the surfaces re finished? Going to get a new ride either way. Just wanted to get an estimate if doing any of this would give me a few months/year of driving the vehicle on the side or possibly selling it.

 

Yep, triple checked the thermostat and water pump.

 

Head gasket symptoms can vary and at times be very elusive.

If the test for exhaust gas in coolant is positive then there is a problem.

Do not recommend a head gasket sealant as can cause more problems then solved however some owners swear by it.

 

I have tried the 'head gasket repair' sealant stuff and I've never seen it work. I guess there is some copper stuff that is supposed to be really good from what I hear, but I would not waste my time.