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Either bad (new) temp sensor, or overheating

billsnogo

New CEG'er
Joined
Aug 19, 2012
Messages
8
I have a 98 contour with 2.0L zetec that used to run around M to A on the "NORMAL" on the temp gauge. When it hit A, the electric fans usually kicked on. Then the gauge worked intermittently, then not at all. I left it be (lazy), but it has recently got colder here, and the heat did not seem all that great, and finally got a CEL, and after reading the code (not reaching proper temp), figured it was the thermostat as that is exactly what happened with my wifes 2000 ZX2 with a zetec that had only 20K on it.

So, I figured while replacing the thermostat, I should replace the temp gauge sensor. Autozone sold me one (don't remember brand, but not motorcraft), installed it and wanted to see if it worked, and sure enough it did, but took no time at all to reach RED. The heat coming out of the vents did not seem all that good, same as the previous week. I then replaced the thermostat, and tried it again. Again the gauge went to hot pretty quick (but not instantly). It seems the fans are not coming on unless I turn the a/c on, so either they stopped working, or the sensor is not sending the correct signal to the gauge. I am to affraid to let the car run too long as it possible could be way too hot. Car does now put out good heat, unlike before.

I have ordered a motorcraft sensor but it will take a week to get it. So as I see it, it could be one of three things.
1. Sensor not reading correctly, fix replace it.
2. Bad water pump (but would I not be getting lousy heat do to no flow?)
3. Blown head gasket, but does not seem to use any coolant, and do you now also loose good heat when you have a blown head gasket?

Any easy trouble shooting I can do while I wait for the new sensor?
 
These cars are a PITA to bleed the cooling system. Possible air pocket in the system. One way to tell I if the radiator hoses get hot or one is very hot and one is cold.
 
I believe that the sensor will report full hot when there isn't a ground. But I am not 100% on this. Not sure if the Zetec always had a plastic housing for the thermostat, but if the sensor doesn't have two wires then it isn't going to read correctly.
 
'These cars are a PITA to bleed the cooling system.'

I do not agree with that even a little bit, the zetec engines pretty much self bleed and instantly if the stat is installed right with its' bleed hole facing straight up. Why all the bleed hoses are on the engines. Like 9 of them. If nothing clogged then engine is bled by the time the stat is fully open, if not you got something seriously wrong. Got 3 of them and all 3 have bled almost instantly every time I mess with them.

They are set up to instant bleed to mix coolant as rapidly as possible so engine can go to closed loop much faster for emissions. Why the hoses to plastic reservoir.
 
'These cars are a PITA to bleed the cooling system.'

I do not agree with that even a little bit, the zetec engines pretty much self bleed and instantly if the stat is installed right with its' bleed hole facing straight up. Why all the bleed hoses are on the engines. Like 9 of them. If nothing clogged then engine is bled by the time the stat is fully open, if not you got something seriously wrong. Got 3 of them and all 3 have bled almost instantly every time I mess with them.

They are set up to instant bleed to mix coolant as rapidly as possible so engine can go to closed loop much faster for emissions. Why the hoses to plastic reservoir.


These cars have a closed cooling system, and air getting trapped is very easy to do. With the radiator cap being on the degas bottle, or coolant reservoir tank, you are sealing the entire system and this makes the bleed process more difficult. Unlike the open system, with the radiator cap being on the radiator itself, and the coolant reservoir being vented, these systems do not automatically bleed easy, or by themselves.
 
Sorry my friend, you are lost..............Closed or open system has NOTHING to do with system bleeding at ALL. They bleed into the airspace in the plastic tank. You either get that and why, or you don't. I have never bled one ever and no reason to EVER do so. The bleed line off top of stat housing does it, on later ones they even add another bleed off top of radiator, again to bleed into that plastic tank. Get one clean and watch the small amount of bleeding that takes place 100% of the time all the time. Where the small hoses enter and why they are there. I have never bled or burped one of these ever, I simply wait till engine warm enough to open stat fully and then cap it up and go on. You may have to occasionally add a very small amount more coolant after a couple more hot cycles, after that nothing ever or you've done something wrong. Done it WAY too many times. Focus cars are the exact same way.

There is pretty much no such thing as 'trapped air' in modern engines, they plumb to every dead flow spot to pretty much circulate all coolant in the engine at all times. That's to get it ALL as hot as quickly as possible to lower cold engine open loop emissions. You must have missed that class. Even the heater loop flows 100% of the time, it never turns off like old ones did.

Put that stat in wrong though and you just created issue where none before.........

You need to go back and look at your old 'open' systems again, they were as closed as these, the top of radiator served as the airspace. The cap sealed to pressure same as these. They bled to top of radiator back then, no difference there. Having cap on or off really does not change bleeding much, the air still goes to high spot in the system. You could cap off, drive for a bit and then uncap to add more fluid. No need now, it happens much faster with all the hoses.
 
I'll give an update in case someone who has a similar problem will get some answers. I installed the motorcraft sensor yesterday, and low and behold, my gauge did not go past "R" in normal, and I get good heat again, so the new thermostat helped with the barely warm heat, and the proper sensor got my temperature gauge working properly. I tend to be cheap, but the extra $15 for the motorcraft sensor over the autozone one is worth it. Live and learn.

thanks all for your help :)
 
Good deal. AS it has been noted in the past Contours and very sensitive when it comes to aftermarket sensors, etc. OEM has always seemed to be the best way to go.


However the temp gauge should have nothing to do with you being able to get heat or not ....
 
Sorry my friend, you are lost..............Closed or open system has NOTHING to do with system bleeding at ALL. They bleed into the airspace in the plastic tank. You either get that and why, or you don't. I have never bled one ever and no reason to EVER do so. The bleed line off top of stat housing does it, on later ones they even add another bleed off top of radiator, again to bleed into that plastic tank. Get one clean and watch the small amount of bleeding that takes place 100% of the time all the time. Where the small hoses enter and why they are there. I have never bled or burped one of these ever, I simply wait till engine warm enough to open stat fully and then cap it up and go on. You may have to occasionally add a very small amount more coolant after a couple more hot cycles, after that nothing ever or you've done something wrong. Done it WAY too many times. Focus cars are the exact same way.

There is pretty much no such thing as 'trapped air' in modern engines, they plumb to every dead flow spot to pretty much circulate all coolant in the engine at all times. That's to get it ALL as hot as quickly as possible to lower cold engine open loop emissions. You must have missed that class. Even the heater loop flows 100% of the time, it never turns off like old ones did.

Put that stat in wrong though and you just created issue where none before.........

You need to go back and look at your old 'open' systems again, they were as closed as these, the top of radiator served as the airspace. The cap sealed to pressure same as these. They bled to top of radiator back then, no difference there. Having cap on or off really does not change bleeding much, the air still goes to high spot in the system. You could cap off, drive for a bit and then uncap to add more fluid. No need now, it happens much faster with all the hoses.
You are totally wrong here. The open systems have vented reservoirs, meaning the overflow tank is vented, and the radiator cap has 2 separate seals, one for the pressure, which releases excess pressure, and a second seal on the neck of the radiator; and coolant as the pressure builds, thus the hot coolant that spills out of the radiator is dumped into the overflow tank, and as the coolant cools, the coolant in the overflow tank gets siphoned back into the radiator. These systems bleed easier because the air pockets move up to the top of the radiator as the coolant passes through the radiator cap to the overflow tank, and a simple 1/4 turn of the radiator cap which opens up the lower pressure seal and air is expelled into the overflow.


A lot of cars have heater control valves, which is a valve that shuts off coolant flow to the heater core depending on heater selector position. Toyotas, GM and older Fords have these valves, which are either electrical or vacuum actuated.
 
Good deal. AS it has been noted in the past Contours and very sensitive when it comes to aftermarket sensors, etc. OEM has always seemed to be the best way to go.


However the temp gauge should have nothing to do with you being able to get heat or not ....


Most cars built from 96 to now work better with OEM parts on the cars. Even more apparent now with the more complex PCM monitoring these days.
 
Good deal. AS it has been noted in the past Contours and very sensitive when it comes to aftermarket sensors, etc. OEM has always seemed to be the best way to go.


However the temp gauge should have nothing to do with you being able to get heat or not ....

Correct, the new thermostat helped with that. Same thing happened with my wifes zx2 with a zetec :)
 
'You are totally wrong here. The open systems have vented reservoirs, meaning the overflow tank is vented, and the radiator cap has 2 separate seals, one for the pressure, which releases excess pressure, and a second seal on the neck of the radiator; and coolant as the pressure builds, thus the hot coolant that spills out of the radiator is dumped into the overflow tank, and as the coolant cools, the coolant in the overflow tank gets siphoned back into the radiator. These systems bleed easier because the air pockets move up to the top of the radiator as the coolant passes through the radiator cap to the overflow tank, and a simple 1/4 turn of the radiator cap which opens up the lower pressure seal and air is expelled into the overflow.

The open system is NOT open, again, you either get that one adds on a closed tank and the other an open tank, or you don't. That has NOTHING WHATEVER to do with how the cooling system works on BOTH, or under pressure at ALL times motor is operating, it cannot function without that. Who cares if one then recovers the lost fluid? The later one never loses it to begin with and bleeding still occurs. Look at the later 'degas' tank and you can easily see it goes on now ONE HUNDRED PERCENT of the time. I'd call that somewhat better than attempting to do yourself for five minutes. The later systems then also add another bleed line to top of radiator to to take care of it even faster. Doesn't really matter as there is NO 'top of radiator reservoir area any longer, they are all crossflow type now. Uh, they wouldn't call it what you do, or a 'degas bottle' if this were true........'this makes the bleed process more difficult.' You're proving out my point with your own words..........

Most start blaming mysterious 'trapped air' issues when they cannot stop a car from overheating, I haven't had bleeding issues ever on a car for over 45 years and I worked on plenty of them. I can generally pinpoint overheat issues in a couple minutes and have never failed to fix them one time and done. It's just not that hard and no reason to put all kinds of non-issues in there to buffalo peoples' minds, they have enough trouble understanding what's really there already. It's the same thing as blaming the PCM when they cannot understand how to fix something and happens all the time. The frail human mind always blames the thing it understands the least.


'A lot of cars have heater control valves, which is a valve that shuts off coolant flow to the heater core depending on heater selector position. Toyotas, GM and older Fords have these valves, which are either electrical or vacuum actuated'

The trend today is away from that, the valves sever off part of the coolant and that increases emissions when that part has to be heated separately. Dead flow coolant is anathema on a modern low emission engine. That loop also results in heater cores going bad much faster, they clog up five times as quick with the flow cut off so trash can settle in them. Why you don't get heater cores clogged nowhere like they used to. Including the heater loop at all times also brings the heater online a couple of minutes faster than having that valve in place, the valve requires a bypass around it and the heater then is not as directly involved in the fluid loop. Putting it directly 'on the freeway instead of service road' if you will then makes the heat come on line faster in winter. And happier customers when they are not freezing their butts off. Many OEMs are now designing the airbox in car to stop/start heat just by closing a door rather than cutting it off with water valves. The valves cause too much trouble. The car can be made cheaper as well so the OEM likes that.

FYI to OP, at least some earlier zetec stats were commonly made that used an incorrect too small disc size to block the heater loop, some may still be on shelves although one would expect most to be gone. I also saw some that had the wrong length on that back disc extension to never seal the disc at all. You should always compare the old stat to new, commonly at least back a bit they were selling parts that did not work and who cares what the part catalog said. The situation seems to have gotten better though, I remember a time when I could not find a zetec stat that would work though. Everything they put down on the counter was the wrong part. If your stat has no bleed hole you can drill one using like 1/16" drill bit, I've done it on plenty of stats that did not have them. If there is a small 'piddle valve' I remove that, they commonly get stuck from corrosion to block your bleed. The engine will never see that small hole other than bleeding more completely of air.
 
Well, now after driving for a couple of days, I notice my fans do not come on unless my a/c is running. Thankfully it is cool here, so it does not go any higher than the beginning of "L" if I sit for a long time. So, are there relays that could be bad? Fuse? Any known issues? I tried doing a search, but everything seems to be on pre 98, or v6 SVT's.

thanks again.

Edit: jumped the green relay and fans come on, black kicked on for a quick second, probably because I pulled the wire right away, it put out a pretty good spark that startled me, so it seems they both kick on, so is that a bad relay then?
 
Well, now after driving for a couple of days, I notice my fans do not come on unless my a/c is running. Thankfully it is cool here, so it does not go any higher than the beginning of "L" if I sit for a long time. So, are there relays that could be bad? Fuse? Any known issues? I tried doing a search, but everything seems to be on pre 98, or v6 SVT's.

thanks again.

Edit: jumped the green relay and fans come on, black kicked on for a quick second, probably because I pulled the wire right away, it put out a pretty good spark that startled me, so it seems they both kick on, so is that a bad relay then?


Could be bad relay, but a bad thermostat also causes the same issue. The fan sensor may not be getting hot enough. Some cars use the ETC sensor, but others use a separate sensor at the radiator.
 
Fans not turning on is a fairly common issue. There are some good troubleshooting threads out there. Having them turn on with the A/C is an indication of what the problem is, as I recall. However I don't recall at the moment what that was ....
 
Probably radiator fan resistor in the fan shroud, they control power to low fan when a/c is off.
 
Well, I replaced the fan resistor, and still no luck. It used to turn the fans on between the M and A, I let it get to the middle of A (which took a while, it is chilly here) and decided to unhook the temp sender that goes to the ECU, the one above the radiator hose and the fans kicked on low for a few seconds before kicking into high. So,,,,,,,

Fans do not come on by them selves
They come on if the A/C is turned on,
they come on if I jump the relays,
they come on if I unhook the temp sender
I replaced the relays
and I replaced the fan resistor.

Any other ideas?
 
'they come on if I jump the relays,...'

Now you have to figure out why the power to turn relay on is not there. Once you replace all the parts you only have wire issues left. Need VOM skills there and a schematic.
 
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