On my way to class today my 3800 fiero threw an engine code, I could of put this in my other thread but I feel it is a different enough situation to have another topic, anyway, the car through a code saying the coolant temp is lower than the thermostat temp, does anybody have any idea what would cause this? Oh and one other thing that might contribute to this, my fan on the radiator is always running, once I start the car it turns on, I would think that is something wrong in the electronics of the car, but I really have no way of knowing.


Hope somebody has some ideas, Chris

PM FIEROFLYER on this one . He is a specialist on those engines here on this forum

[This message has been edited by Robert 2 (edited 01-16-2008).]

all that code means is the car is running colder then it should aka what the temp the thermostat opens at, this very well could be due to you fans being stuck on or becasue it has been hella cold outside. clear the code and if it does not come back i would not worrry about it if it does you may have a problem with your coolent sensor.

It is just the PCM telling you the engine is running colder then it should all though this is a code that is not set very often the problem is most likely your cooling fan running all the time. Check to see if some one has wired the fan relay to be on all the time this would have been done by the green wire at the relay being grounded. Dan

My Malibu threw that code this winter also.
yes, the coolant is colder than the thermostat temp. only ONE thing can cause this: thermostat not fully closing. the fans are irrelevant - being the coolant wont even head to the radiator if it is not hot enough. I got a new thermostat - and have yet to put it in. the warmer days made the code disappear.

but, if you have a temp guage - look at it. it should be around the 1/2 way point. if its at a 1/4 or just above - its running to cold. but, for a SC motor - maybe you wanna leave it, and get a new chip & colder thermostat


edit: also - I have the orange coolant - and its getting old now. it is time for a coolant flush & replacement - this maybe part of the problem - maybe the coolant doesnt act right when its old.

[This message has been edited by Pyrthian (edited 01-16-2008).]

quote Originally posted by Pyrthian: My Malibu threw that code this winter also. the fans are irrelevant - being the coolant wont even head to the radiator if it is not hot enough.

actualy your incorrect. if the fans are running all the time there is more air moving across the engine at all times mix that with really cold temps and you have a colder engine. also if your thep sensor running the the ecm is bad it will read -40 all the time also causeing the code to throw. The code can also be from just to cold out side for the engine to ever warm up, or as you said a thermostat not closeing but unless you have put a fail safe thermosatat it will rarely ever stick open its almost always stuck closed causing it to overheat.

quote Originally posted by pontiacman63383: actualy your incorrect. if the fans are running all the time there is more air moving across the engine at all times mix that with really cold temps and you have a colder engine. also if your thep sensor running the the ecm is bad it will read -40 all the time also causeing the code to throw. The code can also be from just to cold out side for the engine to ever warm up, or as you said a thermostat not closeing but unless you have put a fail safe thermosatat it will rarely ever stick open its almost always stuck closed causing it to overheat.

I HIGHLY doubt the radiator fan moves enough air to cool a running engine. Tho, right with ya on a bad sensor. And, with the dexcool crap - it does make deposits.

If this code (P0128) sets, the thermostat isn't closing fully or just stuck open. The ECM gives the coolant a preset time to reach stat temperature. The ECM also commands the cooling fans on.
This is out of the manual for the code:

Important
The powertrain control module (PCM) will enable the engine cooling fans when certain engine coolant temperature (ECT) diagnostic trouble codes are set.

After the stat is changed, you have to clear the code or the fans will stay on......

------------------
Mick
1986 GT

I'm not a ECM programmer but I do believe that the thermostat temp is set in the code and if your engine runs cooler than that temp for a set time you may throw a code. I'm suspecting that you are running a less than 195 deg thermostat.

It is throwing p0128, I do have a 180 stat, the car is, at running temp, right around 170, I do have dexcool, the orange stuff, but it is like 2 months old, I don't think the fan is grounded, I drove the car many many miles before the engine swap and the car kept in a consistent temp, about 180, until the water pump started leaking.

One thing that might also be important, is the stat is drilled, and when I first got the coolant system set up it got very very hot a couple times, brink of overheating. One thing I am curious about is, is the radiator fan computer controlled, I don't see why it wouldn't be, but I am not sure.

Chris

The fan is irrelevant, no reasonable amount of air is going to force the engine under temp enough to set a code, not unless you are idling in below zero with the fans on full....

Not to mention, this is a Fiero, the radiator fan is nowhere near the engine

I would not worry about it unless it keep coming back, its just telling you that the engine is not reaching operating tempature when the ECM thinks it should be. This could be a stuck thermostat, or a low temp thermostat, though I wouldnt think 180 would be low enough to set a code. Best thing to do would be to scan it and see what temp its running at. Keep in mind running too low will force you rich costing you power and wasting gas.

The cooling fans running constantly will not cause the engine to run too cold, it will cause the engine to take a few extra minutes to warm up but that is it.
Holes drilled into the thermostat will also not affect operating temp by that much but will help to keep air from building up on top of the thermostat.
The PCM controls the fan with info it gets from the temp sensor, stock the temp setting is very high and in some cases by the time the fan turns on it is too late. This is why it is good to have the temp the fan turns on lowered to a more reasonable temp but not low enough for the fan to be on all the time and not lower then the temp of the thermostat.
When I first built my 3800SC Fiero programming equipment was not so easy to come by so I wired up the fan to be on all the time by grounding the green wire at the fan relay. I drove the car like this for a few years and never had any problems with the engine running too cold or the PCM throwing and codes other then for the fan being wired on.
I have worked on quite a few 3800SC cars over the years and have found only found one with bad coolant sensors and it caused quite a bit of trouble but did not throw any codes related to temp.
I would remove the pin at the PCM connector C1 pin 6 to see if the fan still runs all the time, if it does the problem is in the cars wiring or the relay itself. If the fan does not come on then there is a problem with the PCM which can be reprogrammed or replaced very easily. Dan

Running the fans all the time will remove as much heat as possible from the coolant in the radiator, but will not make the enging run cooler than the thermostat temp.

Engine coolant temp is regulated by the thermostat opening at a preset temp, so once the engine reaches 180, the thermostat opens and 180 degree coolant is released from the engine and replace with lower temp coolant coming from the radiator. If the coolant temp in the engine falls below 180 degrees the thermostat closes and allows the coolant to heat up to 180 then releases it.

Now, having a hole in the thermostat allows a portion of coolant to circulate 100% of the time. This can be a small amount or a large amount depending on the # and size of the holes you drilled into it. The coolant flow through this hole will be somewhat dependent on RPM and its impact on engine coolant temp will depend on the temp of the incoming coolant. Cruising on the interstate it is not uncommon to see the engine run 5-10 degrees cooler than the thermostat setting due to a hole in the thermostat (or the thermostat not fully closing).

The heater core does essentially the same thing, but during summer months since the heat is not in use (no air flow across heater core), the coolant going through the heater core loop does not cool down like the coolant going through the radiator, so it has little overall impact on engine coolant temp. However, in the winter months, both the hole in the thermostat and running the heat are componding this issue.

I run a 180 stat (not drilled) in my early model year 99 GTP and it throws no codes.

It would appear you may have your answer in the post here:

http://www.clubgp.com/newfo...e=&smode=&s=#4216142

Reply from ClubGP:

"The PCM program, or BIN file, has to be modified to turn off a lot of the fail codes for things you won't have in the car. The coolant flow code wasn't added to the base code until '99.

My original DHP 1.0 ran a '98 based BIN file and I never got that code because it didn't exist. When I updated my PCM with the correct BIN file for my 2000 I got an SES light for coolant flow because of my colder thermostat".

Well I have a new discovery, my driver side coolant in line is holding pressure even having the car shut off for more than day now and there is no coolant in the overflow tank...

this makes absolutely no sense to me, why wouldn't the coolant level out?

Chris

quote Originally posted by pontiacman63383: actualy your incorrect. if the fans are running all the time there is more air moving across the engine at all times mix that with really cold temps and you have a colder engine. also if your thep sensor running the the ecm is bad it will read -40 all the time also causeing the code to throw. The code can also be from just to cold out side for the engine to ever warm up, or as you said a thermostat not closeing but unless you have put a fail safe thermosatat it will rarely ever stick open its almost always stuck closed causing it to overheat.

if the ecm was seeing a -40 most of the time the car will not start especially when warm since when the ecm sees that temp it goes to full rich to start the car at that temp. also i have seen about 150 t-stat stick open it happens way more then one would think and can cause this problem. in fact my father in laws ford just had that problem when he went huntting in montana he froze his but off with no heat from it.

I would deffenitlly check the t-stat then if its good i would check the coolant temp sensor

Well I have heat inside if I want it, for the short drives I have done it is off, but it is there if I need it, oh and on the stuck open idea, I have coolant sitting in the line all the way to the thermostat, so I would guess that the thermostat isn't having a problem closing.

Chris

Just cause you have coolant in the line does not mean its not open, your entire engine should be full of coolant so if the t-stat is open or closed there will be coolant there. what you would look for is physically look at the t-stat and see if its open or not. since you have some heat i would think that it may be working properlly, Do you have the factory t-stat housing? if you do you can very easily pull the t-stat and check it i mean about 2 min and you can eliminate it. if it checks out good then you need to know what the ecm is seeing which with a scan tool you can know real quickly. you may have a bad coolant temp sensor that is telling the ecm that your running colder then you really are.