p0128 *solved (bad stat)

Batass · Post by **Batass** » Sat Jan 24, 2009 12:26 pm

I've been getting this code for a few weeks now. Truck warms up like normal, its always gotten to the 160* mark in the two years I've had it. I did get a code twice for an evap issue, and once for a random misfire (p0300). Probably due to the I"m guessing still factory plugs and wires. Did half of them so far and need to make or buy a special spark plug socket. I haven't done anything to the truck in a year and a half.

F9K9 · Post by **F9K9** » Sat Jan 24, 2009 12:50 pm

Are you running a lower temp thermostat? You either need to relocate the IAT or run the stock 195* tstat in cooler weather if, you are.

Batass · Post by **Batass** » Sat Jan 24, 2009 2:12 pm

I've never changed the t-stat. I wondered if someone had changed it to a cooler one, but factory gauges are rarely that accurate I thought. More meant for deviations. Its always ran this temperature though. I installed a k&n filter and did some mods to the box a year and a half ago.

I did read something about relocating the IAT, but didn't understand it. I know the motor looks at IAT temp to determine when the motor should be warmed up.

F9K9 · Post by **F9K9** » Sat Jan 24, 2009 2:42 pm

Well, replacing the Tstat with a new one might be the easiest and cheapest fix. It sounds like it is stuck open and not allowing the engine to get warm enough. If, you are not into spending money on mods that somehow spirals out of control, I'd get a good replacement and hope that it is the culprit. A little searching should provide allot of info on replacements in this forum. List henryJ as the author and you should get some good info.

Batass · Post by **Batass** » Sat Jan 24, 2009 2:59 pm

It would make sense, but the motor warms up like normal and at the same temp. I've had cars with stuck thermo's and they took 15 minutes to warm up and never reached full temp.

I don't think the stat is the problem.

F9K9 · Post by **F9K9** » Sat Jan 24, 2009 3:12 pm

Your gauge is definitely incorrect because these puppies are meant to run at 195*. You would have tossed the same code 2 years ago otherwise. Let's assume that the gauges always shows 160*.
A tstat is still your cheapest first attempt to fix the problem. After market gauges and replacing the temp sensor can be considered. I'd try a $10 fix first if, it was me. Hopefully more knowledgeable members will chime in and give better advice.

roadrunner · Post by **roadrunner** » Sat Jan 24, 2009 6:33 pm

I too was getting P0128 a while back. 01 with original T-stat. Replaced with new 195* and no more codes. The original was not stuck when I took it out either. Just didn't warm up quick enough to prevent code set. Others may argue differently but this is the bare truth.

Post by **HenryJ** » Sat Jan 24, 2009 6:41 pm

Easy enough to check the stat. Pop it out and look at the bottom of the bulb for a temperature rating.
It has an o-ring so you can just bolt it back up if it is a 180. Then relocate the IAT.
If it is not buy a new stat and o-ring for replacement.
Coolant will be fine. You will lose less than a cup if you're quick about it.

Squeeze the upper hose to purge air back to the expansion tank once you're done. (loosen the cap a little or flip the lever)

YellowCrewCabber · Post by **YellowCrewCabber** » Sun Jan 25, 2009 11:25 am

Yep, change your t-stat first. I have had the temp code before. From my understanding their is a temp sensor in the engine block which can throw a code for two different reasons. The sensor itself is bad or the t-stat is sticking. I replaced the t-stat no problems since.
Jeff

Batass · Post by **Batass** » Sun Jan 25, 2009 5:10 pm

I hooked up the scanner to it today and it said it was running at 175*.

There are two sensors right? One for the gauge and one that ecm reads?

I took out the truck today and paid attention, the thing warmed up to full temp in a mile and a half.

Maybe it is the stat though, the spring could be wore out and it warms up near operating temp quickly, but takes longer in the last 30 degrees or so. Could that be possible? I noticed a little coolant leaking around the stat area too. I'll just swap it out.

They aren't still the standard small block chevy stats are they? I have some of those laying around.

F9K9 · Post by **F9K9** » Sun Jan 25, 2009 5:25 pm

Batass wrote:I hooked up the scanner to it today and it said it was running at 175*...............................

Change the Tstat already! I can understand not believing the rest of us but, put some faith in HenryJ's advice. 175* will throw the code ever time. Invest $10 and 20 minutes and just do it. If, this isn't the problem then, you will have merely performed some maintenance that is already past due!

roadrunner · Post by **roadrunner** » Sun Jan 25, 2009 5:34 pm

Batass wrote:They aren't still the standard small block chevy stats are they? I have some of those laying around.

NO! Buy the proper one and your problems will be over.

Batass · Post by **Batass** » Tue Jan 27, 2009 9:40 pm

Replaced the stat and all is well. Temp came up to about 195 from 175.

Thanks guys.

F9K9 · Post by **F9K9** » Wed Jan 28, 2009 12:12 am

Batass wrote:Replaced the stat and all is well. Temp came up to about 195 from 175.

Thanks guys.

I am sincerely glad that it worked out. Don't bother calling me if, you pass through my locale. I owe you a severe beating because your noggin' is to thick!

Batass · Post by **Batass** » Wed Jan 28, 2009 10:41 am

I know. It didn't make sense to me, until I hooked up a reliable temp gauge.
Thanks.