auto tranny

pock1

Registered User
hello all i my 93 sc auto i;ve been working on for the last few months .hot weather started last month so i decided to change out the thermostat/needdle was all the wayto the red,but before over heating occured the fam kicked in.the thermostat was a 195 ,so i put a 180 and flushed the radiator.got the car back together put anti freeze in at idle,bleed the system .time to take her out. reverse it.no problem put it drive,(reveres) a few times )to get the tranny warm added half a qt a tranny fluid. off we go...................or not.the car would'nt switch to 2nd:confused: went around the block car was still in 1st and would not switch.wth? check the tranny for leaks .all level. so know i need a tranny..@#$%^&*( i bought this last year and was my daily driver and upgrading her as i had the time and funds. byt the way car has 120k.i think i :shocked the tranny and it took a dump:mad:i did a tranny service 2 months ago....been driving well till this past friday.imma switch out my tranny from my 93 and take out the rebuilt 1 from my 90 cougar that been sitting in my garage(wandering if what to do with it)
 
That's unfortunate. I think you may indeed have shocked the transmission a bit, between the new fluid and the high tempeartures.

One thing to check, in regard to the overheating, is to make sure that the low speed fan comes on when commanded (when you have AC on, for example).
 
Sorry to hear. I would agree with Mazza. Also it is not recommended to run a 180 degree thermostat unless you have a tune that commands the fans to come on at a lower temperature. Your cooling system will get heat soak and overheat.

For example. You run a 180 degree thermostat but your fans do not come on until 220 degrees. The thermostat is literally stuck open all the time at 220 degrees when the fans come on and the coolant in the radiator now has no time at all to cool down. The system should work in such a way where the thermostat continuously opens and closes. Each time allowing enough time for the coolant in the radiator to cool off.
 
Sorry to hear. I would agree with Mazza. Also it is not recommended to run a 180 degree thermostat unless you have a tune that commands the fans to come on at a lower temperature. Your cooling system will get heat soak and overheat.

For example. You run a 180 degree thermostat but your fans do not come on until 220 degrees. The thermostat is literally stuck open all the time at 220 degrees when the fans come on and the coolant in the radiator now has no time at all to cool down. The system should work in such a way where the thermostat continuously opens and closes. Each time allowing enough time for the coolant in the radiator to cool off.

I don't totally agree with the physics model you laid out there, but I do agree that the 180 thermostat can't keep the engine any cooler than the radiator and fans will let it. If they aren't doing their job, a cooler thermostat (or even removing the thermostat) won't help.
 
I don't totally agree with the physics model you laid out there, but I do agree that the 180 thermostat can't keep the engine any cooler than the radiator and fans will let it. If they aren't doing their job, a cooler thermostat (or even removing the thermostat) won't help.

Really???? what part specifically?
 
Really???? what part specifically?

The "too fast to cool" part. I think it's true as far as a specific molecule of coolant will shed less heat if you move it through the radiator more quickly. But you have to also remember that you are moving more molecules through the radiator. So the total heat shed should go up, as long as the airflow across the radiator is sufficient to give the heat somewhere to go.

A downside of slowing down coolant flow is that, although the coolant in the radiator has time to shed lots of heat, the coolant in the engine has time to pick up lots of heat. It can then start to boil in certain spots and lead to hot spots, which are bad.

There's a time delay involved in the movement of the heat from combustion gas to cylinder wall to coolant to radiator to air. If you could move the coolant (and the air across the radiator) at near-light speed, it would be great, because the temperature in the engine and the radiator would be almost totally equalized. Obviously, that's not realistic, because of friction, heat transfer from the coolant to the metals, and other such things. In practical terms, moving it too fast would only cost horsepower. (Assuming you have a thermostat that keeps the coolant from getting too cool.) So you only need to move it fast enough that you can keep the engine temperature in the desired range.
 
The "too fast to cool" part. I think it's true as far as a specific molecule of coolant will shed less heat if you move it through the radiator more quickly. But you have to also remember that you are moving more molecules through the radiator. So the total heat shed should go up, as long as the airflow across the radiator is sufficient to give the heat somewhere to go.

A downside of slowing down coolant flow is that, although the coolant in the radiator has time to shed lots of heat, the coolant in the engine has time to pick up lots of heat. It can then start to boil in certain spots and lead to hot spots, which are bad.

There's a time delay involved in the movement of the heat from combustion gas to cylinder wall to coolant to radiator to air. If you could move the coolant (and the air across the radiator) at near-light speed, it would be great, because the temperature in the engine and the radiator would be almost totally equalized. Obviously, that's not realistic, because of friction, heat transfer from the coolant to the metals, and other such things. In practical terms, moving it too fast would only cost horsepower. (Assuming you have a thermostat that keeps the coolant from getting too cool.) So you only need to move it fast enough that you can keep the engine temperature in the desired range.

I understand what you are saying but I want to be clear. So what you are saying is that it doesn't matter if the thermostat never closes allowing for sufficient time for the fluid to cool off in the radiator?

Regarding the hot spots. That is what the bypass hose is for. Unfortunately it alone isn't enough to keep an engine cool.

I will disagree with you. An engine will over heat with no thermostat for the same reason it wil overheat with a 180 degree thermostat if the fans come on too late.

When the thermostat is closed you want the fluid to pick up heat from the engine. That is its function. You said it. There is a time delay in how quickly the fluid can absorb the heat away from the coolant passages. Just as it is its function to dissipate heat while in the radiator.

you are correct with one regard. The fluid does move faster. Too fast. The fluid has no time to cool off. The heat exchanger, the radiator in this case, has a mechanical limit of how much air you can move through it and you couldn't move enough air through it in a short enough amount of time to cool off the radiator fluid if the thermostat never closes.

A thermsotat doesn't keep the coolant hot or cold. The radiator does. However if the fluid doesn't sit in the radiator long enough to dissipate heat then the system gets heat soaked. The thermostat either allows the coolant to flow or not flow.
 
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My personal opinion: The car won't overheat from having too high a mass flow rate of coolant. Yes, you can move a given molecule out of the engine before it could pick up much heat. But there's another molecule waiting right behind it to take its place. And another. And another. Each one picks up less heat individually, but the total is greater.

The difference in temperature between a molecule just leaving the engine and a molecule just leaving the radiator is caused by the speed of the coolant. Specifically, the lack of speed.

If you let the coolant mosey through very slowly, the coolant coming out of the radiator could be as low as ambient temperature. But the coolant coming out of the engine would be too hot. So it's obvious that coolant can move too slowly.

If you could move the coolant really extremely fast, it would actually be great. The engine and radiator would be a completely consistent temperature throughout. Each molecule would pick up a tiny amount of heat, take it to the radiator, and shed it right away. Obviously, there are mechanical limits to how fast you can pump it through. I am just saying, the heat transfer itself is not a reason to slow the coolant down.

It's the same reason you turn your AC fan speed up on a 100 degree day. You don't say, "Hey, slow that air down so I can get cooler." You say, "Hey, speed that air up so I can get cooler." You are the engine in that scenario. You want a higher mass flow rate to cool down faster.

I definitely agree that, with or without a thermostat, the car won't cool properly without sufficient airflow over the radiator!
 
Of course you want the coolant to move quickly but not until the thermostat opens. You don't want your thermostat to remain open continuously.

The reason you turn the fan up higher on a hot day with your AC on is because the car is heating up inside more quickly. In this example the AC system has excess cooling capacity and you benefit from additional air flow.

Why don't you test our your theory and pull out your thermostat and drive up and down the freeway. I'll bet you overheat.
 
Of course you want the coolant to move quickly but not until the thermostat opens. You don't want your thermostat to remain open continuously.

The reason you turn the fan up higher on a hot day with your AC on is because the car is heating up inside more quickly. In this example the AC system has excess cooling capacity and you benefit from additional air flow.

Why don't you test our your theory and pull out your thermostat and drive up and down the freeway. I'll bet you overheat.

I don't really have time for a needless thermostat swap at the moment, but it would be an interesting experiment.

You're right, there has to be excess cooling capacity in the AC system for my analogy to work. I would think that, in most driving situations our cars will see, there will be some amount of excess cooling capacity that would let out cars run a little cooler than originally designed. Otherwise, they would be dangerously close to overheating on an unusually hot day. (Like old cars before pressurized cooling systems, I guess!)

However, there is definitely a limit to how much cooling the radiator can provide. I mean, you can build and install a 40 degree thermostat, but guess what - the car won't cool to 40 degrees! Maybe that is what you mean by heat soak?
 
:) all I mean is that if a thermostat never closes that means you have a cooling issue. Poor airflow, faulty radiator, low coolant level, etc. would be the cause. If you run a 180 thermostat and the fans come on too late your engine will eventually overheat. Heat soak means the radiator can no longer keep up with demand.
 
:) all I mean is that if a thermostat never closes that means you have a cooling issue. Poor airflow, faulty radiator, low coolant level, etc. would be the cause.

Definitely.

If you run a 180 thermostat and the fans come on too late your engine will eventually overheat.

If the fans come on at stock temperature, then I don't think the car will exceed stock temperature. However, it will overheat in the sense that it's higher than you wanted.

Heat soak means the radiator can no longer keep up with demand.

Ok, gotcha. Interesting point. If you run with no thermostat, you are basically demanding that your engine run at ambient temperature. So by definition, it will be overheated, or heat soaked, since the radiator is not designed to provide that much cooling with such a low temperature gradient. Although it wouldn't be overheating in the sense we usually understand it.
 
when i changed the therostat to a 180 the fan(low speed) kicked in at half way or middle).bleed the system a lil more the needle dropped a lil more.after 15mins the needle stayed in the middle, high speed came on at 3/4 which brought the temp to almost less than half. on the auto tranny the 90 cougar has been sitting for a year,all i took off was the radiator and wrapped the tranny lines(held them up so the don't leak out the fluid)im going to swap trannies.90 cougar xr7 to my 93 sc and hope for the best the tranny works. cougar tranny was rebuilt and switched well be for parked.....any tips i should do ? im not changing the tranny fluid, it's cherry red already.i'll put the rad in over the weekend and run her to see if it tranny still shifts before makeing the swap. i'll be pissed if it cougar tranny dosen't work.:eek:
 
Definitely.



If the fans come on at stock temperature, then I don't think the car will exceed stock temperature. However, it will overheat in the sense that it's higher than you wanted.



Ok, gotcha. Interesting point. If you run with no thermostat, you are basically demanding that your engine run at ambient temperature. So by definition, it will be overheated, or heat soaked, since the radiator is not designed to provide that much cooling with such a low temperature gradient. Although it wouldn't be overheating in the sense we usually understand it.

Sorry man but you are confusing demand with command. The thermostat needs to open and close. With fans coming on too late the thermostat will no longer open and close. I do not know of a better way to explain this to you.


It will absolutely exceed stock temerature wth the "commanded" fan settings turnign the fans on at too high of a temperature.

Again this is all I have to say about this subject. You can keep your stock "commanded" fan settings with a 180 degree thermsotat. It's your party. :)
 
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thermostat

Sorry man but you are confusing demand with command. The thermostat needs to open and close. With fans coming on too late the thermostat will no longer open and close. I do not know of a better way to explain this to you.


It will absolutely exceed stock temerature wth the "commanded" fan settings turnign the fans on at too high of a temperature.

Again this is all I have to say about this subject. You can keep your stock "commanded" fan settings with a 180 degree thermsotat. It's your party. :)

ok so i go back to the stock 195 .
 
Again this is all I have to say about this subject. You can keep your stock "commanded" fan settings with a 180 degree thermsotat. It's your party. :)

Why would I do that? It obviously won't run any cooler if the airflow isn't up to the requested task. I never said it would.


It will absolutely exceed stock temperature wth the "commanded" fan settings turnign the fans on at too high of a temperature.

So what is "too high" with a 195 thermostat? And what is "too high" with a 180 thermostat?
 
Why would I do that? It obviously won't run any cooler if the airflow isn't up to the requested task. I never said it would.




So what is "too high" with a 195 thermostat? And what is "too high" with a 180 thermostat?

Like I said. I don't have anything else to add. :)
 
Like I said. I don't have anything else to add. :)

Ok. See you later. No hard feelings on my end. Hope none on yours.

pock1 said:
when i changed the therostat to a 180 the fan(low speed) kicked in at half way or middle).bleed the system a lil more the needle dropped a lil more.after 15mins the needle stayed in the middle, high speed came on at 3/4 which brought the temp to almost less than half. on the auto tranny the 90 cougar has been sitting for a year,all i took off was the radiator and wrapped the tranny lines(held them up so the don't leak out the fluid)im going to swap trannies.90 cougar xr7 to my 93 sc and hope for the best the tranny works. cougar tranny was rebuilt and switched well be for parked.....any tips i should do ? im not changing the tranny fluid, it's cherry red already.i'll put the rad in over the weekend and run her to see if it tranny still shifts before makeing the swap. i'll be pissed if it cougar tranny dosen't work.

I hope the trans swap goes well. As far as the temperature goes, it sounds like there was some problem. Perhaps the low speed fan stopped working and brought on the high temperatures? I would recommend getting the transmission situation fixed and see how it behaves before changing the thermostat or anything else. Then the first thing I would look at is the fans.
 
Ok. See you later. No hard feelings on my end.

None at all man. I can't articulate my thought any more clearly so I don't see a need in continuing he conversation. I see you on here all the time and to be honest I typically agree with a lot of your direction. Just not this time. LOL And that's Ok. It happens.
 
None at all man. I can't articulate my thought any more clearly so I don't see a need in continuing he conversation. I see you on here all the time and to be honest I typically agree with a lot of your direction. Just not this time. LOL And that's Ok. It happens.

Likewise. Peace!
 
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