98 Avalon... looking for thermostat loc pic

[98avaloner]

Hello gang,

New to this forum...

I'm looking for a clear picture or guidance on the exact location of the thermostat...
I have a Hanyes manual but for the life of me I can't orient the pics in it to the engine compartment... unfortunately, the manual that I have covers Camries (4 & 6 cyl) AND Avalons...

Any help would be much appreciated...

[Brian R.]

The thermostat is almost always inside the housing to which the upper radiator hose is attached on the engine block.

[98avaloner]

Originally Posted by Brian R.

The thermostat is almost always inside the housing to which the upper radiator hose is attached on the engine block.

Thanks, Brian...

The Haynes manual advises to remove the air filter box to gain easier access to the thermostat housing. This filter box is located on the driver side...

The upper radiator hose' on the other hand, is on the passenger side...

How do you rectify?

Thanks again...

[RIP]

I'm assuming you have the 6 cylinder engine. This is from the Factory Service Manuals thread at the top of the Camry forum. I believe it's the same 6 cyl engine: http://www.camrystuff.com/index.php?page=Gen4_Manuals

Open the link and click "Coolant" in the left column. Scroll half way through the manual past the 5S-FE 4 cyl section to the 1MZ-FE 6 cyl section. There's a diagram showing the thermostat on page CO-9. Subsequent pages show replacement procedures.

Here's another source: http://www.autozone.com/shopping/rep...00c152800925f2 Scroll down till you see photos. Click the photos to blow them up.

[98avaloner]

Originally Posted by RIP

I'm assuming you have the 6 cylinder engine. This is from the Factory Service Manuals thread at the top of the Camry forum. I believe it's the same 6 cyl engine: http://www.camrystuff.com/index.php?page=Gen4_Manuals

Open the link and click "Coolant" in the left column. Scroll half way through the manual past the 5S-FE 4 cyl section to the 1MZ-FE 6 cyl section. There's a diagram showing the thermostat on page CO-9. Subsequent pages show replacement procedures.

Here's another source: http://www.autozone.com/shopping/rep...00c152800925f2 Scroll down till you see photos. Click the photos to blow them up.

RIP, God Bless...

That's exactly what I was hoping for... especially, the photos at Autozone resource...

Thanks, RIP

[Brian R.]

Originally Posted by 98avaloner

Thanks, Brian...

The Haynes manual advises to remove the air filter box to gain easier access to the thermostat housing. This filter box is located on the driver side...

The upper radiator hose' on the other hand, is on the passenger side...

How do you rectify?

Thanks again...

I don't. If you look at the link RIP provided, it shows the thermostat at the end of the lower radiator hose. Although this is illogical since the thermostat will be sensing the radiator coolant temperature (flow is from the radiator through the thermostat) and not the engine temperature, I will not second guess Toyota's logic on this one.

This is an exception to the rule.

[98avaloner]

Originally Posted by Brian R.

I don't. If you look at the link RIP provided, it shows the thermostat at the end of the lower radiator hose. Although this is illogical since the thermostat will be sensing the radiator coolant temperature (flow is from the radiator through the thermostat) and not the engine temperature, I will not second guess Toyota's logic on this one.

This is an exception to the rule.

I ain't an expert on this stuff but Toyota's logic makes perfect sense to me...
You see, the sensing part of the thermostat is pointed towards the engine thus it will sense the engine water temp... when this temp reaches the proper value the thermostat will open up and let rad water flow into the engine...

I did mention already that I ain't an expert on it, didn't I? I sure might be wrong...

Thanks for your input...

[RIP]

Originally Posted by Brian R.

I don't. If you look at the link RIP provided, it shows the thermostat at the end of the lower radiator hose. Although this is illogical since the thermostat will be sensing the radiator coolant temperature (flow is from the radiator through the thermostat) and not the engine temperature, I will not second guess Toyota's logic on this one.

This is an exception to the rule.

Ya, I agree. I was thinking somethings wrong with this diagram. That's why I checked the Autozone site. I learn something everytime I open a thread on this forum.

98Avaloner - Glad to hear you're on the way to fixing the beast. Happy to help.

[98avaloner]

Originally Posted by RIP

Ya, I agree. I was thinking somethings wrong with this diagram. That's why I checked the Autozone site. I learn something everytime I open a thread on this forum.

98Avaloner - Glad to hear you're on the way to fixing the beast. Happy to help.

The thermostat is just the "icing on the cake"... the real repair here (even though not a biggie) is flushing the cooling system and replacing the radiator... the shocks go next...

[Brian R.]

Originally Posted by 98avaloner

I ain't an expert on this stuff but Toyota's logic makes perfect sense to me...
You see, the sensing part of the thermostat is pointed towards the engine thus it will sense the engine water temp... when this temp reaches the proper value the thermostat will open up and let rad water flow into the engine...

As soon as it does this, it stops measuring the engine temperature and measures the temperature of the coolant in the radiator hose since the coolant flow at this point is through the hose into the engine. When the entire cooling system and engine are at operating temperature, there is very little difference between the upper and lower hose placement. The difference in thermostat locations is biggest when the engine is getting hot after start-up and the radiator is relatively cold.

The logic is that the thermostat's function is to regulate the engine temperature, not the radiator temperature. Since the engine coolant inlet is from the bottom of the radiator, your thermostat is in the point of the coolant circuit where the first liquid temperature it measures when open is from the radiator. Therefore, it is controlling the temperature of the radiator, not the engine. This is because as the engine heats the coolant near the thermostat, as it opens, the liquid it measures is at the temperature of the radiator. This cooler liquid will shut the thermostat until the engine can heat up the liquid at the thermostat. This opening and closing will continue until the entire cooling system is hot.

This is not controlling the engine temperature, particularly at the top of the engine furthest from the thermostat. I bet the top of your engine gets significantly above operating temperature until the thermostat stays open.

Normally, the thermostat (upper radiator hose placement) is at the point of coolant exit and the thermostat will open just enough to allow the coolant to exit the engine when it sees hot coolant. It open when the engine gets hot and will stay slightly open and allow hot coolant to exit as the engine heats it when the entire cooling system is warming up. This is permitting circulation of the coolant when the radiator is cold and maintains the engine at the set operating temperature. Thereby, controlling the temperature of the engine. This placement of the thermostat (upper radiator hose) allows the thermostat to circulate hot coolant to the radiator at a rate which controls the engine temperature. The other thermostat placement in the lower radiator hose will not open based on the temperature of the hottest coolant, which to me seems less desirable.

[98avaloner]

Originally Posted by Brian R.

As soon as it does this, it stops measuring the engine temperature and measures the temperature of the coolant in the radiator hose since the coolant flow at this point is through the hose into the engine. When the entire cooling system and engine are at operating temperature, there is very little difference between the upper and lower hose placement. The difference in thermostat locations is biggest when the engine is getting hot after start-up and the radiator is relatively cold.

The logic is that the thermostat's function is to regulate the engine temperature, not the radiator temperature. Since the engine coolant inlet is from the bottom of the radiator, your thermostat is in the point of the coolant circuit where the first liquid temperature it measures when open is from the radiator. Therefore, it is controlling the temperature of the radiator, not the engine. This is because as the engine heats the coolant near the thermostat, as it opens, the liquid it measures is at the temperature of the radiator. This cooler liquid will shut the thermostat until the engine can heat up the liquid at the thermostat. This opening and closing will continue until the entire cooling system is hot.

This is not controlling the engine temperature, particularly at the top of the engine furthest from the thermostat. I bet the top of your engine gets significantly above operating temperature until the thermostat stays open.

Normally, the thermostat (upper radiator hose placement) is at the point of coolant exit and the thermostat will open just enough to allow the coolant to exit the engine when it sees hot coolant. It open when the engine gets hot and will stay slightly open and allow hot coolant to exit as the engine heats it when the entire cooling system is warming up. This is permitting circulation of the coolant when the radiator is cold and maintains the engine at the set operating temperature. Thereby, controlling the temperature of the engine. This placement of the thermostat (upper radiator hose) allows the thermostat to circulate hot coolant to the radiator at a rate which controls the engine temperature. The other thermostat placement in the lower radiator hose will not open based on the temperature of the hottest coolant, which to me seems less desirable.

I sure see it differently: ()
First, we’re talking here transient state… what happens until the engine reaches steady working temp.

So say the thermostat is placed at the upper radiator hose… the engine coolant gets hot and the thermostat opens up thus letting hot engine water into the radiator… right away, cold radiator water begins to flow INTO the engine block (which hasn’t even reached the lower end of the operating temp range) cooling it at an “accelerated” rate as the water are still cold… the thermostat is totally unaware, at this stage, of this cold water flow into the engine block… rather, it “sees” still, hot water flowing thru it, out of the engine block, and thus remains open, letting even more cold water in… I assume that this rush of cold water into a warm engine block is not desirable and especially at this early stage where the engine still needs to heat up some more.

Now, in the current setup, the thermostat senses the engine hot water and opens up a little, letting cold water in… right away it senses the flow of cold water and closes up for a very short duration (until the water in the engine inlet “hose” heats up) and it reopens, again, for a short duration. That way, the engine block doesn’t get cooled by a rush of cold radiator water right at the stage when it still needs to heat up some more but rather is introduced to the cold water very gradually.
Now, it’s very possible, and even likely, that “time effects” have been factored in into this design, meaning, the time that it takes the top part of the engine block to heat up to the final working temps, thru the gradual introduction of cold water into the heating engine, making sure that it never actually overheats…

But, admittedly, without a quantitative analysis or some good measured data this might be pure speculation on my part…

[Brian R.]

I see your point. Now that I am paying attention, I notice that many Toyota engines circulate coolant this way. Other manufacturers do it differently. You must be citing Toyota's logic, so I guess fast warm-up is preferable to more controlled warm-up.

I don't understand why I never noticed it. I guess the upper position of the thermostat in the Toyota engines I've worked on fooled me into thinking it was the upper radiator hose that was connected to the thermostat. I will have to pay attention to how Honda and Nissan generally do it.

You learn something new every day....

[98avaloner]

Originally Posted by Brian R.

You must be citing Toyota's logic

I want to assure you that I've not been citing "Toyota's logic" as I heavn't read it anywhere nor consulted with any of their engineers... Should it turn out that we have here "meeting of minds", I'll sure take it as a compliment. Up until this thread I never thought about this issue. "You made me do it"...


And I'm almost ready to hit you guys with a new question but I'll search first the forum and then post it as a new thread.

Thanks again for all the helpful input that I recieved here.

[Brian R.]

Be careful - Thinking can be painful...

That will teach me to rely on my small-block/big-block Chevy experience in regard to Toyotas...