Thermostat Position - theory?

[SHEPPO3930]

Hi all,

I am in the process of building a 4age 20v turbo and yes it's RWD, thus will require a different coolant system. Sure i can simply buy an off-the-shelf conversion kits from SamQ, etc... but that's not how i roll. I always try and do things my way... So it's got me thinking about how to do it, and where the thermostat should be positioned on my set up.

There are two schools of thought:

- Thermostat restricting coolant flow OUT of the motor (top radiator hose) ala old school small block V8's, etc.
- Thermostat restricting coolant flow INTO the motor (bottom radiator hose) ala 4AGE

Is one better than the other in theory (provided they both have a bypass)?

Cheers,
Dave

[petergoudie]

The thermostat blocks the outlet of the head so as to get the fastest warm up (this is also essential for emissions + fuel economy, and that either your carb goes off choke quicker or efi start injector turns off). If you put it down low on the inlet you have to warm up the radiator to engine temp before the thermostat will open. If you are driving the car at the same time, especially if the outside temp is low, it could take a very long time to warm up, if at all.

[alan.chalkley]

Heat always rises and this is especially true when the car is stopped.
Another thing to consider is the position of the sensor for electric cooling fans.

[Hiro]

If you put it down low on the inlet you have to warm up the radiator to engine temp before the thermostat will open.

No you don't. If you look at the way the thermostat sits in a FWD 4AGE, the wax pellet is on the engine-side of the housing, not the radiator side. They run a bypass system so that when the thermostat is closed the coolant is circulated around the engine only for quick warm-up, as it hits operating temperature the thermostat begins to open and allows coolant from the radiator to enter the system, at the same time blocking off the bypass passages.

[petergoudie]

No you don't. If you look at the way the thermostat sits in a FWD 4AGE, the wax pellet is on the engine-side of the housing, not the radiator side. They run a bypass system so that when the thermostat is closed the coolant is circulated around the engine only for quick warm-up, as it hits operating temperature the thermostat begins to open and allows coolant from the radiator to enter the system, at the same time blocking off the bypass passages.

Hiro, I think you missed the point. The question was, is it better to put the thermostat at the top of the engine or bottom. All the thermostats I've seen have the wax pellet facing the engine. Also, does the 4AGE actually have a bypass circuit? As far as I know, they just block the water flow against the water pump until warm.

[trdee]

yes they have a bypass

[Hen]

After reading a some tech article years ago, they claimed that the engine should see the coolant at it's highest pressure (less chance of air pockets and slightly higher boiling point) so the thermostat should sit where the coolant exits the motor.

Though I would guess in practice the differences are minor, if not negligable.

[oldcorollas]

i had thought thermostat at exit of engine is better to provide slightly higher pressure in the block to help prevent bubbles forming..
but when engine is hot, the thermostat is open anyway. plus at higher revs the pump probably has more chance of cavitating, than of the heads hotspots forming bubbles... anyway...

there are images around such as the one below, which show that the water comes IN to the pump via lower radiator hose, then into engine, then out top hose... like normal
but also has bypass that goes past the base of the thermostat and back into pump..

and same for remote thermostat (is this RWD also?)



but then some diagrams suggesting the water goes OUT from pump to radiator... but i think this is incorrect?




anyway, i think your question is incorrect.
unless the water pump is running backwards to normal (normal being pumping water through the block, then head, then out of engine), and you have a bypass, it doesn't really matter where the thermostat is.
reason being that with a bypass, the thermostat is NOT the restriction (in terms of providing higher pressure in engine due to pump).
with a bypass, the thermostat is only there to either let hot water out radiator, or let cooler water in from radiator.
whether it is before or after the radiator does not really matter, but after radiator will have slightly higher pressure in the rad?

does the FWD pump suck water from the base of the block? or does it push water into the base of the block?

[SHEPPO3930]

All 4age's pump water INTO the block.

[oldcorollas]

well.. this might seem obvious, but put the thermostat where you wan tto have the bypass
if you are running a bypass system, then the Tstat is onyl there to regulate the radiator water back into the system, NOT to provide pressure to the block. (err.. i think), since there is always flow.
there may be a restriction at the exit of the head to assist, or maybe not, but with bypass system, the Tstat is not the restriction...

that make sense?

so your Q shoudl be, do I regulate water into the radiator, or out of the radiator.. since the engine has a full circuit all the time