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Discussion Starter #1
Hey all,

So I have my replacement engine installed and a new exhaust system installed, and my Acclaim feels almost like a new car. Nice smooth idleing, and it seems a bit more responsive than my old one that had probably had a failing head gasket for quite some time before it let go. I do have a question about the thermostat, though.

I suspect that the replacement engine has a thermostat with too low of a temperature or is otherwise faulty. After an hour of driving, the temp gauge still had not touched the 2nd line in the "u" on the gauge. I can see it move up and down a little bit like the thermostat is opening and closing normally, but just at a lower temperature than before. The heat also seems to be a bit colder than I remember it being before the swap, further increasing my suspicion.


My question is this: while the vehicle is still warming up, is it possible that the computer would cycle between the warmup and normal modes if the temp drops too low (I believe the correct terms are open and closed loop)? Usually, it seems, my car would consider itself "warmed up" when the temp gauge hit the left side of the "u" on the gauge. Since I'm holding 55 with the cruise on for a few minutes by that point, the torque converter would lock up, and I'm sure that a bunch of other things happen that I can't see.

Today, I was driving, and after I turned up the heat, the temp gauge dropped almost back to the line to the left of the "u" when the thermostat opened. I swear that when it happened, the torque converter unlocked, like the car went back to the mode it is in before it warms up. The rest of the ride the car stayed right around the left side of the "u," never making it to the next line up where it always sat before. To the gurus, was I imagining this? Does the computer have the ability to decide "we're not warmed up anymore, go back to warmup mode." Also, would a thermostat that is the right range allow the temperature to drop so low once the car has warmed up?

I still have the thermostat from my old engine, so I can swap it in to see, but I wanted some opinions first. I've never seen my car stay so cold even though it acted normally.
 

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Correct. Lockup requires coolant temp above 140F.

I recommend a Super Stat thermostat from Stant. A little more expensive, but much better performing. Your car will take a 195F thermostat.
 

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Discussion Starter #4
Thanks for confirming that, guys. Since it requires 140 degrees, is it safe to say that the computer will unlock if the temperature dropped too low? I really wanted to confirm what I thought I felt.

I'll put my other thermostat in (not sure on brand, but it is to spec, less than a year old, and worked well in my old engine) and see if the temps look better. Admittedly, we probably should have put my newish thermostat in right away, but the engine ran good in the old car so we wanted to see what we had. My dad tried convincing me that this is mostly because of the cold weather and that there is no downside to the engine running this cold, but it seems that I found one. I'm sure there are many other things that happen at 140 degrees that affect performance and fuel economy as well.
 

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It will unlock if temperature is too low, and also if too high (overheating).

Running cool will kill gas mileage, promote carbon formation, which leads to pinging; also, oil will wear out and be contaminated faster.
 

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Virginia Gentleman
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Might want to replace the temperature gauge "switch" - at least that's how NAPA had it listed when I thought I needed to replace it. Don't confuse this with the CTS (coolant temperature sensor). The CTS is in the thermostat housing in the 2.5 engine. The "switch" is in the head closer to the passenger side. The switch is a single wire vs the CTS two wire.

Just how "cold" is the ambient temperature?

I agree with Bob that Stant's are the preferred thermostat. I've rarely had problems with them. 195 F recommended. Even if a 180 F was used it should still let it get warm enough though fuel mileage may suffer a bit.
 

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Discussion Starter #7
The thermostat that was in there was identical to the one I had, but I put the one I used in anyways. Both are 192 degree thermostats. I noticed a little difference, more like it tended to hover just inside the "u" rather than on the edge of it. I'll watch it tomorrow and see what happens. Heat seemed a little better on the highway, so I'll chock it up as a win that way.

Temperature was probably 20 degrees, probably a bit colder this morning. Maybe the thermostat won't make a difference, I was just baffled that it cooled enough to unlock the converter. Maybe checking out the sensors won't be a bad idea. I have the old motor sitting there yet, so it's not big deal to swap parts.
 

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Doug D said:
Might want to replace the temperature gauge "switch" - at least that's how NAPA had it listed when I thought I needed to replace it. Don't confuse this with the CTS (coolant temperature sensor). The CTS is in the thermostat housing in the 2.5 engine. The "switch" is in the head closer to the passenger side. The switch is a single wire vs the CTS two wire.
The 1-wire gauge sensor is only used for the gauge. It is not used by the computer for any decisions, only the 2-wire CTS is used by the computer. So replacing either won't help.
 

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Bob Lincoln said:
The 1-wire gauge sensor is only used for the gauge. It is not used by the computer for any decisions, only the 2-wire CTS is used by the computer. So replacing either won't help.
Bob, I understand that. I know it is used only for the gauge. What I am suggesting is if the gauge sensor/switch is faulty it can result in a faulty gauge reading.......
 

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Right, but that in turn won't lead to the torque converter unlocking.
 

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I have always had winter warm up issues even after replacing thermostats. I would always get an error code of 17. Newer models would get a P0126. If heater perfomance is poor, don't waste you time with sensors. I have had best results getting a stat from the dealer. Stant thermostats are not what they used to be.
 

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The standard one isn't. But the Super Stat is superior, doesn't float back and forth as much when it opens, and keeps the engine temperature closer to the normal range.
 

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Are you sure you got all of the air out of the cooling system? It sounds to me like you could have an air bubble. My 94 Spirit would do strange things on the temp gauge until I got it burped properly.
 

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This also sounds and is acting like the system still has a little bit of an air pocket in it, turning the heater on made it shift a little bit, and colder fluid entered the system. My understanding of the temp drop back to a different computer loop (open/closed, I always get them wrong), it would set a check engine light, so, unless the external temp is near freezing to cause this,(this may make an exception to the CEL coming on), it is something to check before changing the thermostat, which seems to be cycling since the gauge does seem to move when it opens and closes, Stant is one I would recommend, too.
 
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