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Old 03-20-2009, 11:37 AM   #1
dc_johnson45
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Bad Cylinder Head Temp Sensor?

Hi all...

I've posted about this problem before, but I've done a little work in replacing things - I'm left wondering what the heck the problem is.

Ok, my 2002 Focus Zetec has the temp gauge climb as I drive it above 60 mph. I've replaced the relays and resistor - no help. I even installed the fan mod (both fans always on) and it didn't help. I've had the thermostat changed, radiator flushed & new coolant. Same problem.

I'm left with two things - the Cylinder Head sensor or the water pump. When I put the dash into diagnostic mode and monitor the temp, the gauge starts moving away from the middle when it hits 208C. It gets closest to the red line (never crosses it, but mostly because I slow down - I've never pushed it) the dash is reading 214C. I'm wondering if that is actually too hot? Is 214C pushing overheating the engine?

I have a Cylinder head temp sensor on hand - so I'm thinking I should just go ahead and replace it. The water pump is a bigger issue & kinda beyond my abilities...

Any ideas on what I can do to test things?

Thanks!


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Old 03-20-2009, 01:17 PM   #2
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Do the water pump too. Not over your head by any means, quite easy actually. Just a matter of can you drain coolant and remove bolts. Even a little how-to --> http://www.focusfanatics.com/forum/showthread.php?t=153483

Reason being is generally speed related issues are because of the water pump not moving coolant or worst case blown head gasket (not pouring white sweet smelling smoke don't worry).
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Old 03-20-2009, 01:58 PM   #3
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The possible problem with the water pump......the impellers on the pump are partially rusted off. This causes less pressure, less circulation.

I've seen this a few times, but it is a very unusual problem, and normally caused by not changing coolant for a long time. The coolant would have looked a rusty color when it was finally changed.
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Old 03-20-2009, 04:04 PM   #4
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Ok.. thanks for the advice. My problem really is lack of garage space. I spoke with someone about removing the water pump and they were worried about messing with the timing belt.. something about special tools and the DOHC? That how-to doesn't seem to make it sound too bad (err.. well, except lowering the engine ;-) Were they way off, or should I be reading between the lines on that how-to?

I will say, the coolant was most likely neglected in this car.. I'm not the original owner, so I'm gonna assume the worst. So, sounds like I should tackle the water pump...

Oh, and no white smoke, so at least I'm in the clear there...
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Old 03-20-2009, 04:38 PM   #5
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You won't have to touch the timing belt, so no worries there.
and lowering the engine is a lot easier than you think. It's simply having a jack under the engine and loosening the 2 bolts on the engine side, leave the bolts in to keep the engine from dropping too far. You won't have to touch the other 2 mounts.
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Old 03-20-2009, 06:26 PM   #6
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water pump can be completed in about 2 hrs tops, hardest part is not overtorqueing the water pump bolts.. think it's 156 INCH LBS! can be replaced with basic hand tools.
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Old 03-20-2009, 06:41 PM   #7
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Just curious, does the HOWTO method differ from the recommended Ford way of replacing the water pump?
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Old 03-20-2009, 07:16 PM   #8
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First: how many miles are on the engine?

Water pumps generally last 150k or more. I wouldn't start worrying about one until you get over 150k. There are 2 conditions that water pumps will take to show they are bad. First- coolant will leak from the snout of the water pump. You will have coolant loss. Second, it makes a LOT of noise like knocking. You'll think that your engine is completely coming apart. Never in all the 22 years I've been messing around with engines have I seen impellers rust away to nothing. I've taken apart engines that were more than 30 years old- and these still had water pumps with impellers. Rusty yes, completely gone, no. There's not been a lot of change in the materials used in water pumps either since if you made the impellers out of aluminum or thinner steel it would shatter and smash stuff up under warranty. Besides, it's not like all the fins would disappear at the same rate exactly until these were gone, and that would cause condition #2 of water pump death.

Are you losing coolant? If so, have you checked your exhaust to see if it's coming from there? Do your coolant hoses look bloated and are extremely hot? If your hand comes back moist after you've held it near your exhaust stream at the tail pipe, and you have some of these other signs you could have a bad head gasket. I would not go jumping to that conclusion just yet because of how intrusive it is- you need more signs for that one IMO.

Here's a strange but true one that we had happen recently- change your spark plugs. It costs $6 or so, and it might be the entire problem. Spark plugs pull heat from the combustion chamber and transfer it to the coolant in the cylinder head. If you have a cracked spark plug, it won't transfer heat as it should, and the engine will over heat. This is a cheap one- remove the plugs and inspect carefully- especially the porcelain inside the threads- you'll see cracks or damage if there is any.

Personally, I don't think it's overheating, and 214C should be fine for the cylinder head. Rubber hoses are only good to 225F before the rubber starts to break down- you'd see bloated hoses if your coolant was 214C- if not totally melted!!
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Old 03-20-2009, 08:51 PM   #9
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id check the coolant sensor before digging into the water pump. for what it's worth, my water pump leaked out the weep hole at 75k!

if the engine was infact overheating you would be loosing coolant out of the overflow tank, steaming, bloated hoses, fans kicking on constantly...if you don't have any of these signs then it points to the coolant temp sensor giving false readings and needs replaced
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Old 03-21-2009, 06:13 AM   #10
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^^^^I agree you need to check the actual temperature of the coolant using some other method, before doing any more repairs. Stick a thermometer in the overflow tank and see if the temp is close to what the ECU is reporting. Sensors fail or give faulty readings often enough.

Concerning rusted-off impellers on a water-pump......rare sort of problem, but a possibility. I've seen it three times on Nissans over many years. Those impellers were steel, and can certainly rust. It's a tough problem to diagnose. Look in the overflow tank and you should see the coolant circulating pretty fast if the engine is really hot. If not.....you've got a circulation problem somewhere, causing over-heating.

Other possibilities....clogged radiators cause over-heating. Run your hand over the entire radiator while the car is running.....there should be no spots that are much cooler than others. Even new radiators can be faulty with restricted cores...something you can't see. If you have a non-contact thermometer (looks like a little gun), checking temperatures is very easy.

Once I saw a body shop repair on a Nissan Stanza.....they routed the serpentine belt wrong after the repair. The water-pump was running backwards. The owner ran the car for three months this way, no doubt over-heating. Eventually the top plastic tank of the radiator melted, and coolant sprayed out. No matter how long you work on cars, you'll never see everything......
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