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Discussion Starter · #1 ·
I'm in a fight with my car.

When my engine blew a while back, it was running fine temp-wise prior. The new engine overheated when I took it on it's maiden voyage, and I thought it was a problem with the fans. I rigged the fans up to a rocker switch, and manually controlled their use. I hooked everything back up, and the fans only came on when the temp gauge spiked to the H. I figured the lows weren't coming on, so I changed out the CCRM and the low speed fan resistor, only to find the same problem. I ran some date logging, and the PCM was saying the temp was around 190-200 when the gauge on my dash was hanging around H. Bad switch?

When I changed heads and whatnot, I threw in the LIM from my old engine, which was running fine for temp, with the same temp sensors. Same problem. And I know it's not my gauge, because in the cooler weather, driving at a constant speed brings my temp back to the normal range on my gauge. The computer then thinks it's 160, while I have a 180 t-stat. What's going on with my car? The temp sensor from my old LIM was working fine before, did sitting cause it to go bad? I don't want to throw money into sensors I don't need. Can anybody offer other suggestions as to what it is?
 

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This is one of those system problems you have to understand to diagnose it correctly.

If your cooling system isn't healthy then your're most likely headed for problems.

Is the radiator partially clogged? Have you been maintaining the cooling system (e.g. flushing at regular intervals)? Your heater core is a smaller version of your radiator. If you get no heat from your heater this may indicate a clogged radiator.

If the thermostat is 10yrs old or older I would recommend at least testing it or replacing it with a motorcraft thermostat.

Rumor on this board are the impellers of the water pumps have been known to "disappear". I believe this is more common on the Duratec engines.

If it was me I would start with the least cost item and move up the food chain. In this case the thermostat. You may want to pressure test the cooling system as well. These checks are inexpensive but critical to have a healthy cooling system.

If you can get your hands on a diagnostic tool (autoenginuity.com) you can verify engine temps via the OBD-II interface. Of course you'll will have to depend the sensors are giving the computer the correct values. This could prove to be a valuable diagnostic tool to help troubleshoot the cooling system.

In scenarios like this I mostly rely on common sense, experience and research (e.g. Haynes Manual).

Monsoon
 

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Cake monster
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New engine or engine job? Can you tell for sure if it's overheating, it's not hard to tell when an engine has run hot, it will smell funny, stumble and miss, poor power, etc... Any real symptoms of overheating? If so, then you should fix the overheating issue before worrying about the sensors. Like someone said above, clogged rad, broken or missing impeller on water pump, bad hose, bad tstat, something is causing the cooling system to run at half its capacity. It's possible that there's something wrong with the head job you've done, how does it run when you first start it? Really well? Ranger head gaskets would cause an overheating situation with the engine, wouldn't it? What happened to the engine anyway?

You should post a few extra details to make it easier for everyone to figure this out, be more specific about what you actually did.
 

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Discussion Starter · #5 ·
This is one of those system problems you have to understand to diagnose it correctly.

If your cooling system isn't healthy then your're most likely headed for problems.

Is the radiator partially clogged? Have you been maintaining the cooling system (e.g. flushing at regular intervals)? Your heater core is a smaller version of your radiator. If you get no heat from your heater this may indicate a clogged radiator.
Heat runs hot enough to boil water.

If the thermostat is 10yrs old or older I would recommend at least testing it or replacing it with a motorcraft thermostat.
T-stat's only a month old, at the most.

Rumor on this board are the impellers of the water pumps have been known to "disappear". I believe this is more common on the Duratec engines.
Water pump's changed. I thought that, too, but the old pump was fine after I took it off. Impeller was perfect, and no play in the shaft.


If you can get your hands on a diagnostic tool (autoenginuity.com) you can verify engine temps via the OBD-II interface. Of course you'll will have to depend the sensors are giving the computer the correct values. This could prove to be a valuable diagnostic tool to help troubleshoot the cooling system.
SCT flash tuner, has data logging. That's how I know my engine temp is around 170 while I'm doing 70 mph down the highway with a 180 degree t-stat, and that it's allegedly running at 190-200 when my dash gauge is hanging around H.

I'm lost-did you swap the engine or just heads?
Both. Cooked the engine when my CPS seized and the consequential loss of oil pressure led to a spun bearing. Used engine from the boneyard went in with ~30k miles on it. Then I mildly modified a set of heads and threw them on recently.

New engine or engine job? Can you tell for sure if it's overheating, it's not hard to tell when an engine has run hot, it will smell funny, stumble and miss, poor power, etc... Any real symptoms of overheating? If so, then you should fix the overheating issue before worrying about the sensors. Like someone said above, clogged rad, broken or missing impeller on water pump, bad hose, bad tstat, something is causing the cooling system to run at half its capacity. It's possible that there's something wrong with the head job you've done, how does it run when you first start it? Really well? Ranger head gaskets would cause an overheating situation with the engine, wouldn't it? What happened to the engine anyway?

You should post a few extra details to make it easier for everyone to figure this out, be more specific about what you actually did.
Engine runs fine at startup, and even better at operating temp. No noticeable issues when it spikes to the H, but it's still within the while confines of the gauge, it's not going beyond (at that point in time, the pcm thinks it's warm enough to turn the fans on). It might be absolutely fine, and my gauge in the dash is wrong, but then why is my engine temp falling below my t-stat temp while running?

The gaskets aren't ranger gaskets, and the head swap wasn't the problem, because it was doing this before I changed the heads. Clogged rad, maybe, though.
 

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A couple of concerns here. 1st just because you have a new thermostat (I'm assuming a non-motorcraft) doesn't mean its not failing. You have to verify its not failing by testing it. And I don't mean in the car. Boil the thing like a lobster and see if it opens all the way.

2nd if the block or heads have been overheated at least once you could have cracks in the block or heads with coolant leaks. That's why it's important to pressure test the cooling system (cold). Blown head gaskets are a good indication of an overheated engine as well (e.g. coolant in the cylinders), coolant leaking between the head and block.

Pump-up the cooling system to 15lbs and look for leaks. If you see the pressure gauge approaching zero, look for leaks, everywhere. If you see no leaks but the gauge keeps moving, worst case scenario you probably have an internal leak within the block or heads.

Pulling the dipstick may be able to verify this by noting antifreeze mixed with the oil.

If you find nothing wrong you may want to consider rebuilding your cooling system from the ground up. Using a checklist of the key activities you have already done as well as using quality parts. Sometimes using a checklist will jar you memory of something you forgot.

The Temp Gauge...if the gauge reads HOT but the engine runs well and does not appear to be overheating then the temp sensor may have gone bad.

Monsoon
 

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Cake monster
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170 to 200F seems pretty good to me. I would be interested to know the tranny tempeture though. If the engine gets hot enough, the hi speed fan setting should come on, so I'm wondering if it does. Personally, I don't think it's an overheating issue, other than the guage, what other sign do you have that it's actually getting hot, is it boiling over? My temp gauge acts funny, but I still get good readings when I plug a scanner into the car.

I say take it to a garage and tell them you think it's running hot and that you want to know what the cause is, they should find it within an hour. Just an idea. If you don't want to do that, run it and make it actually over heat, where it's noticable. If you can't do that then I think you're worrying about nothing. I don't believe the tstate closes right at 180, if you want it to be higher than 170 while crusing down the highway, get a higher rated tsat. 195F is stock.

Give it a 25 minute drive, then park the car in your driveway and idle it for 20 minutes, if you have cooling issues, they will show up by then. :D Might not have an engine if there actually is an issue though. If you did a head job, there's always the probability that there's something wrong there. Any CEL?
 

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There are two senders. One is for the dash gage and the other is for the PCM (ECT).

To test the dash gage take the connector off the sender and ground it. It should go full hot or cold (can't remember). Then apply 12V to the wire it should do the opposite.

The PCM sender is what turns on the fans. Normally they should come on around 210F or so.
 

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I bought the sensor (the one that the PCM is supposed to monitor).....but I am not sure which is which.....There appears to be two.....standing at the drivers side fender (right side of engine there is one facing me...then there appears to be another facing towards the firewall to the right of it.....I want to replace the sensor that talks to the PCM
 

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Usually the single wire dash sender has a brown plastic base. The 2 wire ECT (CTS) usually has a grey plastic base. Be sure the new one has some thread sealant applied or a couple of wraps of teflon tape. Usually comes with thread sealant applied.
 

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After '96 the two sensors look alike. Both use the same connector but one has two wires and the other one. Look too see how many pins are on the sensor.
 

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I just know the connector is the same for ECT and temp gage after '96.. The '96 and earlier had the old style single post sensor for the temp gage and the two wire clip on senor for the ECT.
 
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