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Discussion Starter · #1 ·
Hello Everyone,

Here's the short story:
My engine threw a code P0128, got it checked, drove away, engine was overheating, replaced the thermostat, test drove, stayed constant, drove again, and engine overheated. Tested the old thermostat in 200 degree boiling water, and it opened up. I'm not sure what's wrong.

Long Story
I have a 2004 Honda Pilot with 201000 miles 2nd owner, I've loved having it. Yesterday morning the check engine light came on, I just assumed it was a loose gas cap or something, but decided to go to Autozone at the end of the day and have the codes checked. Unfortunately, it wasn't just a loose gas cap, it threw the code P0128, I hadn't noticed anything crazy happening with the temperature before then. I started driving home, but quickly noticed the temperature gauge going far above the resting point at the middle. I never let it get too high. I decided to replace the part Autozone had recommended, the thermostat. I replaced it correctly, with the air hole upright, and topped the car off with the coolant. When I turned the car back on the check engine light was gone. I took it for a test drive about 2-3 miles to the gas station without a problem the temperature gauge hung constantly just below the middle. On the way back from the gas station the gauge started edging up above the middle. It seemed to react to when I had my foot pressed on the gas and when I was coasting. When I got home, I decided to rev up the engine to see if the car would cool down it down, but the needle just went up and stayed there. When I turned off the car the fan kept running for a while after. It's a cold windy day here, so I don't know what would be happening if it was the middle of summer. I boiled some water with a candy thermometer and got it to about 200 degrees and put in the old thermostat, it opened up like it was supposed to and closed when I took it out and it cooled down. So now I'm not sure the thermostat was the problem. Looking back the check engine light probably only turned off because I disconnected the battery to get to the thermostat. I did not bleed the air out of the cooling system after I replaced it, and I've heard that can cause overheating.

I'm at the end of my wits, I really don't know what else could be wrong with it that would trigger that code. Do I need to change my coolant temperature sensor? Could it be a water pump? Has anyone had similar issues? Any suggestions and help would be really appreciated.
 

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The t-stat does one thing only….maintain minimum coolant temp. The rest of the cooling system components and driving conditions determine maximum coolant temp. What else has been replaced? Are efans working? Never place a t-stat in boiling water.
 

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It sounds like you have an issue with the fans coming on. Like PLT383 was saying. The thermostat really helps the system warm up and maintain a steady temperature. The other part of that system is the two electric fans at the radiator and the temperature sensors that tell them to come on. You said that you increased the engine speed trying to cool the engine off but that doesn't really work with a system using electric fans instead of the old school belt driven ones.

The P0128 is a good indication that there is an issue with the cooling fan part of the system. The first thing that I would do is see if the radiator fans are coming on. There are two fans. One should turn on and off when the engine gets to operating temperature. The other fan runs when you turn on the AC. So, warm it up and see if the one fan cycles on and off. Then, turn on the AC and see if the other fan comes on. That would be a good first step.
 

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Internal failure on water pump, impeller spinning on shaft. Kind of rare but does happen especially as the pumps age. Water pump driven by timing belt. Listen for a worn pump at the front and top of the engine (passenger side) a long screwdriver held to the timing cover and to the ear can assist in listening for a bad pump. If you have to change the pump make sure you align all the timing marks first. I don't recall off hand if the 04 had two timing marks on the crankshaft pulley one red and one white but the second mark (red) is TDC. Better yet align the marks on the crankshaft timing belt pulley to the 12 o'clock arrow on the oil pump housing. Crankshaft bolt is 180 ft lbs torque not 47. Pictures show where water pump is located.

Other things that will overheat an engine, low oil, plugged/restricted heater core. Loose belt (not in your case because the timing belt drives the water pump), low fluid due to leaks or evaporation. Air trapped in cooling system. Blown head gasket as coolant leaks into cylinder and combustion gases leak into cooling system. Will see bubbles in cooling system. Can do block test for that. Take off radiator cap idle engine and look for bubbles in radiator and use block tester on radiator to look for color change (blue to yellow). And as HunterTN said cooling fans not working.
 

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Discussion Starter · #7 ·
Thank you for all the replies. Although there was coolant in the reservoir when I checked last night, after driving this morning with the new thermostat, even though I topped off the reservoir, it was totally empty. I ended up driving it onto an auto-ramp and I opened up the radiator cap and burped it. There were some bigger bubbles that came out, but other than that there was nothing, and after they came out it remained without bubbles for 15 or so minutes until I turned the car off. The fluid level did not reach the top of the radiator so I added quite a bit through the radiator cap. I gave it another drive after burping and filling it up with coolant and I couldn't get the the temp gauge to budge above the middle. I even had the A/C running at full blast in the middle of winter to try and coax it up. It wouldn't even raise when I was in neutral revving it up to obscene rpms. I have noticed increased intensity in a slow oil leak that was already there when I bought the car... It makes me worry that it is a blown head gasket. I can't say the last owners were the best at taking care of their pilot, but hey I can't beat 20,000 repair free miles out of a car I bought for $900! It's good to learn how to fix all of this considering my parent's 05 pilot is probably next in line for the same problems.

I considered that the radiator and/or the heater system being clogged. There are some symptoms, the heater is really only lukewarm, even if the car reaches operating temperature, until you start driving and pushing the pedal. I checked the fans, and they appear to be working properly. After the airing out procedure and driving, the fans turned off with the car, and didn't stay on, probably because it wasn't at some ridiculous temperature in the first place. As for the pump, if it is it, I'm going in for a timing belt replacement really soon, so I'll get that replaced. I'm about to take it back into town so I'll be on the freeway, I'm going to keep close attention to the temperature for the foreseeable future.
 

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You must remove the radiator cap when the motor is COLD to properly fill the cooling system. Also, check the bottle when the motor is COLD. It may take several checks over several days, again motor COLD.

Turning on a/c also turns on efans, to cool the condenser.

Time to start investing in reliability.
 

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Thank you for all the replies. Although there was coolant in the reservoir when I checked last night, after driving this morning with the new thermostat, even though I topped off the reservoir, it was totally empty. I ended up driving it onto an auto-ramp and I opened up the radiator cap and burped it. There were some bigger bubbles that came out, but other than that there was nothing, and after they came out it remained without bubbles for 15 or so minutes until I turned the car off. The fluid level did not reach the top of the radiator so I added quite a bit through the radiator cap. I gave it another drive after burping and filling it up with coolant and I couldn't get the the temp gauge to budge above the middle. I even had the A/C running at full blast in the middle of winter to try and coax it up. It wouldn't even raise when I was in neutral revving it up to obscene rpms. I have noticed increased intensity in a slow oil leak that was already there when I bought the car... It makes me worry that it is a blown head gasket. I can't say the last owners were the best at taking care of their pilot, but hey I can't beat 20,000 repair free miles out of a car I bought for $900! It's good to learn how to fix all of this considering my parent's 05 pilot is probably next in line for the same problems.

I considered that the radiator and/or the heater system being clogged. There are some symptoms, the heater is really only lukewarm, even if the car reaches operating temperature, until you start driving and pushing the pedal. I checked the fans, and they appear to be working properly. After the airing out procedure and driving, the fans turned off with the car, and didn't stay on, probably because it wasn't at some ridiculous temperature in the first place. As for the pump, if it is it, I'm going in for a timing belt replacement really soon, so I'll get that replaced. I'm about to take it back into town so I'll be on the freeway, I'm going to keep close attention to the temperature for the foreseeable future.
If you burped the system and the temperature stayed around operating temp you should be fine. As for the lukewarm heater core a less than full cooling system can cause that as well. Start with the simple things, such as a air purged cooling system. Run the vehicle for awhile and see if it overheats or loses coolant if not then you can rule out a head gasket leak unless you see a big puff of smoke out the exhaust when you drive and your having to poor coolant into the reservoir/radiator. If you don't have overheating issues after making sure the cooling system is purged of air an still have lukewarm heat at the core after driving for a few minutes than the core is clogged. You can reverse flush that by taking off the two hoses from the heater core and running water backwards through the core. The core is a mini-radiator with thinner tubes than the radiator and can easily clog. Again start with the simple especially since changing the blend door motor can be arduous. How much rust was in cooling system when you removed the thermostat? Flakes? Very rusty orange? Could you see through the coolant? BTW a cooling system pressure tester can pinpoint pinhole leaks in radiators/hoses. Don't pressurize the system more than the psi on the radiator cap.
 

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Just another little thing to check for: a slow leak in your hoses, connections or radiator. It can happen.

Motor vehicle Gas Font Automotive exterior Auto part
 

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Discussion Starter · #13 ·
Again, thank you all for the help, it really does mean a lot. I love this forum. As an update, I took it on the freeway with no issues, and have drove it a couple times since still with no issues. I checked the reservoir this morning, it appears to still be above the low mark, it's hard to tell the level. I took off the radiator cap and it's filled to the brim with no bubbles in neither the radiator nor the reservoir. I'm going to keep checking it regularly. I wanted to check the tailpipe smoke this morning, but it ended up being useless. It's cold enough that not only my car is blowing some white smoke, but every other car on the road. I'll have to check it after classes today, letting it run adequately.
When it comes to what I saw replacing the thermostat, it seemed really clean. The only indication of rust I saw was along the outsides of the thermostat seal. I saw no trace of rust, not even a flake inside the housing itself. I could see through the coolant, it was translucent light blue.
If I lose coolant, it really would be a good idea to check for leaks. I know I'm jumping ahead of myself, but in the contingency that it was a head gasket leak, what do you all think of that blue devil chemical sealant? Seems like it should fall into the snake oil category if it wasn't for the over 1000 good ratings on amazon. I guess you could say I'm preparing for the worst.
 

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One item I bought years ago that's super handy is one of this "fill funnels" for cars. It attaches to your radiator and allows you to run the car up to full operating temps with a full funnel attached to the top of the radiator. It tends to get WAY more air out than trying to burp air out as the car pukes hot coolant all over the place.

Basically you attach it, and fill it about 1/3 - 1/2 of the way up the funnel and maintain it at that level throughout the process. Then start the car. Turn the heat on, but on the LOWEST fan setting possible - you want coolant flow through the heater core but you don't want much air volume to actually cool the coolant. Then you let it idle, and idle, and idle, and rev it up a bit, and squeeze hoses, etc. Eventually the car will get hot enough to open the thermostat and all the radiator hoses to get hot. At this point you rev it up a few times, squeeze some hoses a few times then squeeze the upper radiator hose slightly, put the plunger in the funnel and take the funnel off. Then install the radiator cap, fill the overflow bottle to the max (maybe slightly over) with the coolant still left in the funnel. Then over the next couple days just check the overflow bottle and top up slightly if needed. Typically it gets enough air out that you'll only have to add a little to the overflow.

This isn't the funnel I have, but it's very similar:

 

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If I lose coolant, it really would be a good idea to check for leaks. I know I'm jumping ahead of myself, but in the contingency that it was a head gasket leak, what do you all think of that blue devil chemical sealant? Seems like it should fall into the snake oil category if it wasn't for the over 1000 good ratings on amazon. I guess you could say I'm preparing for the worst.
Just an FYI: that pic of the corroded radiator was my Pilot and the full extent of corrosion/leak was only revealed when the radiator fans were removed.
 

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One item I bought years ago that's super handy is one of this "fill funnels" for cars. It attaches to your radiator and allows you to run the car up to full operating temps with a full funnel attached to the top of the radiator. It tends to get WAY more air out than trying to burp air out as the car pukes hot coolant all over the place.

Fill funnels are awesome! They make it so much easier.
 

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Again, thank you all for the help, it really does mean a lot. I love this forum. As an update, I took it on the freeway with no issues, and have drove it a couple times since still with no issues. I checked the reservoir this morning, it appears to still be above the low mark, it's hard to tell the level. I took off the radiator cap and it's filled to the brim with no bubbles in neither the radiator nor the reservoir. I'm going to keep checking it regularly. I wanted to check the tailpipe smoke this morning, but it ended up being useless. It's cold enough that not only my car is blowing some white smoke, but every other car on the road. I'll have to check it after classes today, letting it run adequately.
When it comes to what I saw replacing the thermostat, it seemed really clean. The only indication of rust I saw was along the outsides of the thermostat seal. I saw no trace of rust, not even a flake inside the housing itself. I could see through the coolant, it was translucent light blue.
If I lose coolant, it really would be a good idea to check for leaks. I know I'm jumping ahead of myself, but in the contingency that it was a head gasket leak, what do you all think of that blue devil chemical sealant? Seems like it should fall into the snake oil category if it wasn't for the over 1000 good ratings on amazon. I guess you could say I'm preparing for the worst.
Haven't used it myself but have talked to a dozen guys who swear by it. But, don't get ahead of yourself, slow down, it could be the system needed purging. Keep an eye on the coolant level. You'll see some evaporation, furthermore coolant shrinks/expands with heat so the over flow during colder weather will seem lower, the opposite is true for warmer weather, the reason for the MIN-MAX scale on the bottle. Stay in the range and should be fine if nothing else is going on. As for the radiator funnel have those myself, works great, better than the old way of the bleeder screw on the thermostat housing found on mid-later 80s/90s GM. That little air bubble would sometimes cause overheating on their V-6.
 

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Thank you for all the replies. Although there was coolant in the reservoir when I checked last night, after driving this morning with the new thermostat, even though I topped off the reservoir, it was totally empty. I ended up driving it onto an auto-ramp and I opened up the radiator cap and burped it. There were some bigger bubbles that came out, but other than that there was nothing, and after they came out it remained without bubbles for 15 or so minutes until I turned the car off. The fluid level did not reach the top of the radiator so I added quite a bit through the radiator cap. I gave it another drive after burping and filling it up with coolant and I couldn't get the the temp gauge to budge above the middle. I even had the A/C running at full blast in the middle of winter to try and coax it up. It wouldn't even raise when I was in neutral revving it up to obscene rpms. I have noticed increased intensity in a slow oil leak that was already there when I bought the car... It makes me worry that it is a blown head gasket. I can't say the last owners were the best at taking care of their pilot, but hey I can't beat 20,000 repair free miles out of a car I bought for $900! It's good to learn how to fix all of this considering my parent's 05 pilot is probably next in line for the same problems.

I considered that the radiator and/or the heater system being clogged. There are some symptoms, the heater is really only lukewarm, even if the car reaches operating temperature, until you start driving and pushing the pedal. I checked the fans, and they appear to be working properly. After the airing out procedure and driving, the fans turned off with the car, and didn't stay on, probably because it wasn't at some ridiculous temperature in the first place. As for the pump, if it is it, I'm going in for a timing belt replacement really soon, so I'll get that replaced. I'm about to take it back into town so I'll be on the freeway, I'm going to keep close attention to the temperature for the foreseeable future.
The empty overflow tank is a big red light that tells me a head gasket failure is highly likely. You need to do a coolant residual gas test. It's not too expensive. If your oli is not a milkshake it is likely that for the moment, you have a leak that is not yet dripping into a cylinder.

The fix it in a bottle will not help for long. ChrisFix on YouTube has an interesting video you should watch on the subject. Doubtful it would make sense to pay to have this fixed.

Did you overheat the engine once? That is the usual source of these problems

Astrobuf
 

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Hello Everyone,

Here's the short story:
My engine threw a code P0128, got it checked, drove away, engine was overheating, replaced the thermostat, test drove, stayed constant, drove again, and engine overheated. Tested the old thermostat in 200 degree boiling water, and it opened up. I'm not sure what's wrong.

Long Story
I have a 2004 Honda Pilot with 201000 miles 2nd owner, I've loved having it. Yesterday morning the check engine light came on, I just assumed it was a loose gas cap or something, but decided to go to Autozone at the end of the day and have the codes checked. Unfortunately, it wasn't just a loose gas cap, it threw the code P0128, I hadn't noticed anything crazy happening with the temperature before then. I started driving home, but quickly noticed the temperature gauge going far above the resting point at the middle. I never let it get too high. I decided to replace the part Autozone had recommended, the thermostat. I replaced it correctly, with the air hole upright, and topped the car off with the coolant. When I turned the car back on the check engine light was gone. I took it for a test drive about 2-3 miles to the gas station without a problem the temperature gauge hung constantly just below the middle. On the way back from the gas station the gauge started edging up above the middle. It seemed to react to when I had my foot pressed on the gas and when I was coasting. When I got home, I decided to rev up the engine to see if the car would cool down it down, but the needle just went up and stayed there. When I turned off the car the fan kept running for a while after. It's a cold windy day here, so I don't know what would be happening if it was the middle of summer. I boiled some water with a candy thermometer and got it to about 200 degrees and put in the old thermostat, it opened up like it was supposed to and closed when I took it out and it cooled down. So now I'm not sure the thermostat was the problem. Looking back the check engine light probably only turned off because I disconnected the battery to get to the thermostat. I did not bleed the air out of the cooling system after I replaced it, and I've heard that can cause overheating.

I'm at the end of my wits, I really don't know what else could be wrong with it that would trigger that code. Do I need to change my coolant temperature sensor? Could it be a water pump? Has anyone had similar issues? Any suggestions and help would be really appreciated.
It could also be a bad water pump!
 
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