My car has been throwing engine codes lately. This happened immediately after I added some sea foam to the gasoline, so my first thought was that it was just an error message from that nothing to worry about, so I clear it, add some more gas, it came back on later, I cleared it again, it went away for a while, then this morning it came on when I started it up again. I was getting a p0128 and p1000 and just realized that is a coolant thermostat error. Since I just had problems with my cooling system and had to replace a broken coolant tank a couple weeks ago, I think this is probably related. Not sure what to do. I have fresh coolant in there and everything had been working great up until I added some sea foam to the car. Not sure if the thermostat is bad now or if it's just giving me a mistaken code. Looked up thermostats and they aren't too expensive, just wondering how much trouble it is to replace them and if there would be anyway to fix a stuck one. Maybe it had something to do with when it overheated the day my tank broke. Anyways, the weather has been warming up as well, but I doubt that is the cause of it, the code seems to come on when I start up the car.

 

The code is basically saying that the engine temperature is different than what the thermostat temperature should be regulating.
A low coolant level could cause this as well as a inoperative cooling fan.
In most cases it is the thermostat. If you do end up replacing it on your own, make sure you clean the mounting surface of the thermostat housing with some Scotch Brite pad. If not it may leak.

 

Does the temperature gauge on the dash register properly?

 

Oh good, I'm glad you said that because I popped the hood and the coolant reservoir level was at the minimum mark so I topped it off with some fresh coolant after clearing the code and the code hasn't returned yet after driving it around a little. I had filled it up to the maximum a couple weeks ago so I was a little surprised it was on minimum already, unless it had some bubbles still in the system. I will have to keep an eye on it. I had put a little bit of this coolant system leak seal in there just in case there was a little leak, but I'm not sure there even was a leak, it was more as a preventative measure. All it seemed to do was make my coolant brown. We'll see if the level flucuates now that all the bubbles have gotten out of the system from when the coolant tank was replaced.

 

Unless you had some coolant repairs done to it it shouldn't have any air pockets. Some common places to look for leaks
- expansion tank outlet pipe (small pipe on top)
- outlet pipe o-ring (front of engine by engine mount held on by 8mm bolt)
- pipe o-rings within engine Valley (need a flash light to look all the way down the valley)
- thermostat housing (between cooling fan and engine under air cleaner housing)

 

Don't forget the water pump. Very common in our cars that they eventually wear out. Mine went right at about 100K. Started with a very slight leak. Made an appointment at my mechanic to replace it and they were just pulling into the bay and it fully went. Coolant was just pouring out. So, if the water pump is leaking you are definitely living on borrowed time. Hope your leak is more minor than that.

 

So I cleared the 3 codes, p0128, p1000, and unknown error, and filled up the coolant level back up and it goes away for 2 days and I think great, it's solved. Then I start'er up this morning and the dang check engine light pops back on! I check the coolant level and it's fine, it's about half way between min and max, I think I may have lost some but am not sure since I filled it up on a bit of a tilt. So I'm not sure what to do. I suspect it is due to the crap coolant system stop-leak I put in for no real reason when I flushed the radiator. All it did was make the coolant a goopy murky brown color. Also I noticed my coolant hoses are starting to bulge. I never noticed this before but they are definitely starting to look a little worn and probably due for a change. Not sure what the problem is with the check engine light though. Could be the coolant, could be the thermostat, could be the sensor, could be the sea foam I put in the gas tank. I'm guessing it's the thermostat is clogged or stuck and needs replaced. But also doing the hoses might be an expensive project. The thermostat hose alone was $150. I found a set of upper radiator hoses on ebay for $50. Anyone know a good source for x-type radiator hoses? Should I try to just change out the problem-looking hoses? Also what do you think the cause of my check engine light is? What would your first step be? I was hoping it would go away but it seems to be persisting and the time of year is warming up soon.

 

I did just find this on justanswers about an x-type with the same code:

"Yes a code P0128 will cause the engine light to come on but there may be other codes also stored. If the thermostat was replaced and they did not use the correct mixture of coolant and water it will cause this problem or you may have a faulty engine coolant temp sensor. Have the codes rescanned to see what they are. You can go to your local autozone who will scan for the codes at no charge to you if pepboys will not."


That could be the problem. There may be more water than coolant in the system, plus the stop leak gunk, because I was not thinking and forgot there was some water still in the engine when I went to fill it back up with 50/50 mix. Then realized it was watered down. Drained a little out and added more 50/50 mix and then the stop-leak pellets... Maybe my first step would be flushing the radiator again.

 

P1000 is just saying the monitors haven't all cleared since the last time the codes were cleared.
If I were you I would start with the thermostat. If you just replace the hoses I'm pretty sure the check engine light would return.

 

Thanks. I will do the thermostat next. My first plan is the coolant. The coolant it has in it is almost brand new but I put like half a bottle of coolant system stop-leak in it after I had filled it almost all the way up. I probably did the directions wrong. They were the gummy brown pellets and they turned the beautiful neon green coolant into brown sludge water. Two weeks go by and it's driving fine then all of a sudden it's been starting to throw CEL codes. I am thinking the gunk is starting to clog the thermostat or maybe it's triggering the sensor into thinking something is wrong with the coolant. It is probably a little more water than coolant. I messed up my 50/50 calculation when I was adding coolant because I forgot to factor in the water left in the engine block and started adding a 50/50 mix to it. I didn't think it would matter since it is warmer weather now, I thought the antifreeze was mainly for winter, but according to that Jaguar mechanic, a p0128 code can indicate a mixture of coolant that is not 50/50. I am hoping that is it. I probably should drain the rest of that stop-leak crap out of my coolant system anyway, and fill it up with fresh coolant. I'm hoping the check engine light doesn't return but if it does, I'll try flushing it out with fresh coolant. Hoping I can still save my thermostat if I caught it early enough and get that stop-leak gunk out of the system. I read it can clog radiators. Car seems to be running better with about half a gallon of fresh coolant I added today. Has that new coolant smell again. May have to get another gallon of coolant and flush the rest out this weekend. Figure I will take this problem in baby steps. The hoses I can replace anytime. It's just a matter of spending the money and doing them. I think they have some life left in them still. Could probably use the upper radiator set. Maybe do that later this year.

 

So I drained out the murky coolant and filled it up with fresh Prestone. Some of that brown stop leak is still in the system though because it's not perfectly neon green yet, but a good amount of the coolant is fresh now. I cleared the code and thought it would fix the problem but it came back on today. It kind of pissed me off. I hoped the coolant was triggering the check engine light, but now I'm guessing it's the thermostat. Not sure if I should try flushing the coolant again and risk wasting more coolant or just go ahead and get the $100 hose and thermostat. I read today that thermostats are a problem for the x-types and will trigger that code, so it is likely the thermostat, I'm just not sure why it's going now. Maybe it was the stop-leak that did it in. If so that sucks.

 

So I checked the coolant level just now when I cleared the Check Engine light. It's giving me the exact same 3 codes: N/A, p0128, and p1000. The coolant level had dropped down to just below minimum from when I drained and filled it the other day, probably some air was in there that adjusted the level. Anyways, I am HOPING that is the problem. Most likely the thermostat is going bad, since I read they can be a problem on the x-types and tend to trigger that p0128 code. My other option is to buy another bottle of coolant, and do one more drain and fill and see if the code goes away with a complete fill of good coolant (no-stop leak). If the stop-leak already messed up the thermostat though, I doubt that will reverse it, but it could be worth a shot. If it doesn't I will have to drain that fresh coolant out. So I'm kind of stuck. Maybe I should wait it out a week or two and see what the check engine light does.

 

From reading other p0128 threads on here it sounds like it is most likely a faulty thermostat, possibly from when my coolant tank broke and my car briefly overheated. Also I tried patching it up and drove it for a few days til the tank arrived. Probably not a good idea in retrospect. Then when I got the tank, I flushed it and filled it with new coolant and stop-leak pellets, which also could have F#@&ed the thermostat up. So all in all, that is three things that could have possibly messed up the thermostat, not to mention they seem to fail on their own anyway with age. Guess I should just buy that new radiator hose with the thermostat and do the install. Thing that sucks right now though is I am also in the middle of doing my suspension so it's kind of like 2 big different projects at going on at once, but I knew this was a problem before I started my suspension.

 

Ok, went ahead and bought the new top radiator hose assembly w/ thermostat. Figure the old one is most definitely shot, no bother driving around like that and wasting time dumping good coolant in it to realize that the thermostat is just going bad. Plus I heard those hoses are prone to leaks anyways, so best to replace the whole top radiator hose assembly than just the thermostat. Anyways, looks like a pretty big project. Looks like I need to put some gasket sealer on it and let it dry 24 hours, so it will have to do it over a weekend.

 

It sounds like you have a leak somewhere if the coolant level keeps going down. That's a lot of fluid lost to got from the max level to the min level, especially more than once. When you replace that thermostat really look around to see if you can see anything wet, especially the water pump. Those seem to go around 100K. Good luck, hope it is a simple job.

 

I am hoping the water pump is fine. So far I have no reason to believe it is a problem. I think the coolant level is due to me draining and filling the coolant and not checking for air bubbles adjusting the level. The other day I drained and refilled my coolant level and forgot to watch for the level to adjust. Also, it may be a leak around the thermostat or the top radiator hose assembly. I was reading that those are a real common problem. If I was leaking anything it was a very slow leak. I hadn't really had a problem with leaking coolant though, just my coolant tank broke a few weeks ago and spilled out most of the coolant and the fans kicked on (only drove it about 5 or 10 mins though when it happened). Today the check engine light popped back on, so it's definitely probably a bad thermostat. I will keep the water pump in mind though and look for any leaks or signs of leaks from that. I heard it's an easy repair, but it's another $100 part. So if it is being a problem I will have to change it but hopefully right now it's just the thermostat.