djkidd

I had a check engine light pop up on my dash board. The engine temp gauge won't go past 1/4, where it would normally be at 1/2 when the engine was fully warmed up. When I ran the diagnostic tool from Autozone, I got the code P0128. Does this sound like the thermostat needs to be changed (I have 150K+ on the ODO)? If so, how difficult would it be for me to do on my own? I think Autozone had the part for like $10-20. Thanks!

Edit: I have a 2015 Lexus GS350 F-Sport (thanks @LexusGSboy for pointing out the missing information)

LexusGSboy

So just for folks who might be looking at this and might be able to chime in:

Code P0128 - Coolant Temperature Below Thermostat Regulating Temperature. The OBDII trouble code P0128 - Coolant Temperature Below Thermostat Regulating Temperature means that the engine does not reach expected temperature after running for sufficient time, or in other words, takes too long to warm up.

Also for the OP - you might let us know what MY this is, just in case it makes a difference. I'm also assuming it's a 350 and not one of the others like at 200t or a 300.

I was just curious about this post as I'm trying to learn more about the GS. In old school days, this easily sounds like it could be the thermostat - they could get stuck open or stick closed. In those days the only indication you got was watching your temp gauge. Often it could be a pretty simple fix since the thermostat was often sitting up where the upper radiator hose connected to the engine.

On a GS it'll take someone with more knowledge than I have to chime in. From what I found in photos/parts diagrams, it seems like this should be pretty straight forward and it looks like it's in a housing up near where the upper radiator hose connects but I have NO idea how hard it is to get in there nor if you need to replace the housing for any reason. There will usually be a gasket and you may need gasket cement. If it does need those things make sure to take a razor blade and clean off all of the old gasket and cement so you get a good seal. Again, I don't know enough about the GS to know for sure so do a bit more research.

Personally I would do an OEM thermostat - either from Lexus or if you can find who was the original manufacturer. On one car I had issues with after-market thermostats, about every 2-3 years I'd have to replace it. Luckily it was about a 15-30 minute job on that car so it wasn't a huge deal, just more of an annoyance.

LexusGSboy

I found this video where he says that that code is related to the thermostat. This is NOT for the GS but for an RX and a different V6 Engine but seems like it could be similar.


It looks like it comes down to how hard it is to get to the thermostat on the GS. Hopefully someone else may know the answer to that question.

703

CAKETOWN

iTrader: (7)

This video shows coolant drain and thermostat removal/replace on our lexus gs.. if you have to do it.. might be useful.

Starts at 15:58, not sure why timestapping it doesnt work on the link.


Also i would agree to get the oem lexus parts.

LexusGSboy

This is great - I searched and couldn't get anything to come up on the GS. All comes down to search terms probably.... Love learning about the GS. Thanks for finding it!

Only other thing I'll mention - you definitely need to make sure you get all the air back out of the system. On a different make/model car had a dealer not do that and the car started to run hot going up hills on a trip a few days later. No major damage or long term problems but it was a lost day on vacation while another dealer checked things out to see what was going on.

CAKETOWN

iTrader: (7)

Yea no problem, yea pretty common knowledge you have to get the air out of the system, those big funnels with the plugs do a good job for that.

Dealerships are last resorts, sorry to hear that they cost you a day on vacation, it's why i try to do all my own work.. you pay with your hard earned dollars and they don't even do it properly.

imjohnphan

I had this problem on an ES that I used to own. It was the Coolant Thermostat that was stuck open so coolant was constantly being pumped into the radiator preventing for heat to build up in the engine.

djkidd

So I went back to Autozone tonight and was talking to the guys there. They were surprised to hear that the thermostat could go bad already. They basically recommended trying a burp of the system first and if that doesn't work, to check if the thermostat is stuck. Perhaps may not need a new thermostat so I'll update this thread as I discover more.

What did you do to fix your issue on your old ES?

imjohnphan

Hi for my old ES I just replaced the thermostat myself. It wasn't too hard honestly.

LexusGSboy

I'm completely happy for someone to correct me if I'm wrong on any of this but.....

I've never heard or seen an issue where things run cool when there's air trapped and unless the coolant was allowed to get really low or was recently changed there shouldn't be a way for air to get in. From my experience when air gets in things tend to run warmer because the water can't flow properly. Cooler would indicate the water is running too well. The only situation I could think of where air would be an issue would be if it happens to be sitting right where the sensor is for the gauge/car reaching operating temp. Maybe - but then I'd go back to my earlier comment about how did air get in the system all of a sudden.

A thermostat, from what I know, even on these cars, is a pretty simple device. It's a piece of metal that expands and contracts with hot and cold and a spring. As the water heats up, the metal expands, pushes against the spring and opens up so water/more water can flow (I may have that backwards but that's the rough idea). As the water cools the the metal shrinks and starts to restrict the flow so that things warm back up.

Thermostats can go for a number of reasons - the spring gets week, the metal that expands and contracts somehow comes loose, corrosion develops so things can't move freely. At 6 years and 150k I wouldn't think it's out of the question that it's having an issue.