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 Post subject: Thermostat Stuck Open?
PostPosted: Mon Nov 13, 2006 12:39 pm 
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Location: Silicon Valley
Hi Folks,

While driving my van to the airport a few weeks ago (2001 Chevy Venture) I noticed something strange - the Temperature gauge was at the BOTTOM of its range, or VERY low. I had noticed that the temperature gauge HAD started to rise at the beginning of my trip, and I had the heater on because it was kind of cool that morning (about 50 degrees F).

Anyway, the gauge stayed pretty low throughout the trip (about 30 minutes @ 60+ MPH), and the heater was NOT working as well as I think it should have (I had to turn the temp control dial all the way up to get any warm air).

On the way home from the airport a few days later, the gauge seemed to be stuck low for a while BUT then suddenly came up to about 1/4 scale on the gauge (where it "normally" sits).

:?: So here is my question: Could it be that the thermostat is stuck (or sticking) OPEN?

Normally I would just change it, but on this van that can be a bit of a pain because the thermostat housing is not exactly "in the clear" or easy to get at. So before I tackle this job I would like to get a couple of other opinions.

All input is appreciated.

Take Care,


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PostPosted: Tue Mar 13, 2007 7:37 am 
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 Post subject:
PostPosted: Mon Nov 09, 2009 10:37 pm 
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I have the same problem on my 185,000 mile 2001 Venture. OBD II code P0128. Thru much research via the 'net changing the thermostat is a hit or miss proposition. Personally I wouldn't mind swapping out the thermostat, however the genius's at GM decided in their infinite wisdom to stuff the damn thing behind the exhaust crossover pipe. :shock: I'm sure it would be a fairly uneventful repair if the engine wasn't in the car but...

Anyway, seeing as how the fans are also on now full time and at high velocity, and the fans should not come on unless the engine temp is higher than normal, and the heat from the vents is only semi-warm, it seems to me that the logical cause would be a fan relay or faulty fan temp sensor. Unfortunately, the print-out from Auto Zone (they read and deciphered the code for me) did not mention anything about the fan. The print-out did however state that
Quote:
the PCM verifies that the engine is at a proper operating temperature.
so I am kind of confuzzled as to exactly what is going on. But I just can't explain the reason for the fans to be running. There is no logic.

The fans I am thinking, could be the cause for the lower temperature reading. The temp gauge worked one day and not the next. The fans were off one day and on the next. So I went to the 'net to see what I could find out about this P0128 code and I was directed to this web address:
http://www.obd-codes.com/p0128
where I found this:
Quote:
Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:

-Verify coolant strength & level
-Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
-Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
-Verify proper intake air temperature (IAT) sensor operation, replace if necessary.

If the above items check out good, replace the thermostat
If Nissan vehicle, check for a TSB such as this one. The ECM may need to be reprogrammed to correct the P0128 code


This has given mefaith (and hope) that it could very well be that when I disconnect the fans I will again have the temp gauge working as it should. I'm sure I'll get another code saying the fans aren't working but I'm going to wager the P0128 code will also be gone.

I know this won't be replied to untill after I d the testing, but I am curious as to what others thoughts are on my way of thinking.

And also, I wanted to comment on something that is related but still OT; I have found loads of the same problem(s) I have with my Venture all over the 'net. People ask and there are some with answers and some with no replys. What I find incredibly selfish and impolite is that the original posters don't take the time to come back after they resolved (or eliminated) their issue with what they finally did. Did they fix it and if so, what fixed it, or did they say enough is enough and just get rid of the vehicle? I have wasted countless hours on my problem and have had to read others stories only to be left hanging as to what the actual cure ended up being. Regardless if my issue is the fans relay(s), I will reply back here in the hopes it may help someone else down the road.

As a whole I do like the Venture. I would never recommend one to a friend though. Not unless it was a really good deal anyway.


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PostPosted: Tue Nov 10, 2009 12:14 am 
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Hi Splicer,

Thanks for your response. I believe the P0128 code and the fans running when they are not needed is a result of the thermostat either leaking or stuck open. I did a little research into the GM maintenance manual for that code, and there was something in there that says that the PCM will turn on the fans as a "safe-mode" measure when it thinks there is a possible problem with the sensors related to the cooling system. I guess they figure it is better safe than sorry when it comes to running the fans.

So I don't think the fans running is the problem, but rather a symptom of the other problem (thermostat). I also have a lot of "physics" evidence that the thermostat is not functioning properly, such as the temperature gauge that varies when I am going down a long downhill stretch of road. The temperature gauge just continues to drop, even at relatively warm outside temperatures (in the mid to high 70's).

The way I understand it, the thermostat is suppose to block the flow of coolant between the block and the radiator, and should only be open above the rated temperature of the thermostat (195 for these engines). And I can tell you, my engine does not stay at a stable temperature around 195 at all, unless I let it idle in a drive through line, or have a long uphill road to go up. But as soon as the van is moving through the air again, the temperature drops.

I will let you know what happens when I finally get my thermostat changed (yes, I have still not changed it). Its too much of a pain to get to it myself, and I really don't want to pay to have it changed, but that might happen soon, if the funds become available.

Take Care,


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 Post subject: Fixed! Done! Over with!
PostPosted: Tue Nov 10, 2009 3:16 pm 
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Thanks for the quick response Greg. First off I must say that if after 3 years that you haven't changed the thermostat yet, that there is no reason to at this point. But enough about you, as promised I am ready to tell the fix for my Venture. BTW, thanks goes to you for your fuse/relay block photos. That was a huge help, and I should have thought to consult my owners manual first, but you had the pretty color photographs. :wink:

Back to business; Just as I suspected, the fans running on high was the problem. With the engine running, I removed the #9 5 pin and #10 4 pin relays to shut the fans off. I then felt the lower radiator hose start to warm up. With a smile on my face (smiling is optional) I sat in the drivers seat and waited for the temp gauge to start registering. A couple of minutes later, VOILA! The needle moved to the normal operating location. I had full heat from the heater again and I knew damn good and well that all was right in the Venture world once again. I reinserted the relays and the fans stayed off. I took the parts I bought from Auto Zone and returned them, told them of their blunder with not mentioning the fans, and asked them to reset the PCM P0128 code. While they gladly refunded my $$$, they denied my request to clear the code. Something about they aren't supposed to and it will clear itself in a few days of driving. So we will see, if not I will get my own scanner and that way I won't have to take the van anywhere when the CEL comes on again.

The main reason I avoided swapping the T-stat (besides the nasty location) is because in all my years of working on cars, and all the cars I have owned with T-stat problems, I have NEVER had one be stuck OPEN. Closed yes, but open, never. I don't know how one could be stuck open. Leaking very possible, open is not from my expanded experience. Anything is possible, which is why I entertained the idea but being stuck open is so very unlikely.

With this in mind, lets diagnose your "symptoms" that makes you believe you have a faulty T-stat.
Quote:
I also have a lot of "physics" evidence that the thermostat is not functioning properly, such as the temperature gauge that varies when I am going down a long downhill stretch of road. The temperature gauge just continues to drop, even at relatively warm outside temperatures (in the mid to high 70's).
This is normal. When you are going down hill, gravity pulls the car and the engine is not working as hard. Thus, the engine temp will drop. Also with the lower altitude the engine will cool faster as the air moving thru the radiator is thicker and can absorb more heat.

Quote:
And I can tell you, my engine does not stay at a stable temperature around 195 at all, unless I let it idle in a drive through line, or have a long uphill road to go up. But as soon as the van is moving through the air again, the temperature drops.

If you have a good cooloing system (clean, clear radiator, properly working water pump, good hoses with no soft spots, and working T-stat) the engine temp will indeed vary. Again, you altitude and location has alot to do with just how well your cooling system is working. You don't have any of that Dex Cool crap in your system do you? When the van is in a drive thru line it will heat up. Mine does. I don't use the drive thru for that reason and it is a needless waste of gas and wear and tear on an engine/tranny, and I can just as easily get out and walk in the place myself.

A perfect example was today when I let the van idle while waiting for the temp gauge to start registering. Once it was at normal, I still let it idle longer because I knew the temp would raise. As well it should. The fans were off (thankfully) and there is no air moving thru the radiator. As a result the temperature raised to the 1/2 way mark on the temp gauge.

After I reinserted the fan relays and I lowered the hood, I took the unneeded parts back to the store. Driving there, the temp expectedly fell to its normal temp. Nothing out of the ordinary here. Also, you can run your heater and the result will be a lower temperature due to the fact you are drawing heat from the coolant.

From what you have posted, the worse case scenario for you is a leaky T-stat. That won't hurt a thing as long as you are not leaking coolant from the goose neck or elsewhere from the engine. The T-stat would be the last thing I would be concerned with. However it is your van and obviously you know better than I the whole picture, and I am only basing my opinion(s) on what you wrote.

You never mentioned the fans being on or off in your posts, so you may not know either way. But I encourage you to look into it Greg, as this could be an added, unnecessary strain on the electrical system if allowed to continue needlessly. You can also check the temp sensor that, while easier to get to than the T-stat, is still a PITA to get to.

Finally, I have the same problems as you (and most others I've found) have;
-gas gauge screwed up. What I do is fill the tank and use the tripometer and when I reach 400 miles I fill it again and zero out the trip for another 400 miles.
-A/C filler valve leaks. I have filled the system a few times. When it works, the A/C works well. 3 days later it is like I never did anything. Dye in the 134A indicates the valve is leaking. I replaced the valve, still leaks. Never replaced the whole tube due to low funds. Should I do that, I cringe that the condensor will come up cracked like yours. I am not going to sink $700 into the A/C. We can live without it, hell, we have for the past 3 years :wink:.
-The rear window motors barely operate and can't be used. I'm not going to spend $100 per just so the rear most windows can open. The sliding doors windows are fine.

So there you have it. I hope I have been able to help you and others with this cooling issue and P0128 code. :D [/i]


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 Post subject: Re: Fixed - Done - Etc.
PostPosted: Tue Nov 10, 2009 4:06 pm 
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Hi again,

Thanks for the response. I would say that you should definitely get your own scan tool, or perhaps just a code reader, depending on the funds that you have available and what you plan on doing with it. I actually have both, a code reader that I got from Harbor Freight and use for reading and clearing codes, and another "toy" (BR-3), which I use for gathering data. Maybe you saw my page on the main site about the Engine Cooling Cycle? I used that tool to gather the data for that page.

My main concern about the engine running a a "lower than normal" temperature is "What does it do to gas mileage?" As you may know, most modern vehicles are controlled by "the computer" and one of the factors that controls how much fuel is injected is the engine temperature. I don't know how much bringing up the temperature to around 195 degrees would effect the mileage, but it would be an interesting experiment.

The other concern I have is how LONG it takes to get any decent amount of heat inside the van in the winter! I live in the San Francisco bay area, so winter is not too harsh, but even driving on a long flat highway (I-5) to visit family during the holiday season can be trying when the heater has to be cranked to the highest temperature setting to just stay warm during these trips. But I have a plan for that ... I am planning on putting a "wind blocker" in the front of the van that will stop some of the air from hitting the radiator as we are driving (an old truck driver's trick). We will see what happens with that. :lol:

Take Care,


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 Post subject:
PostPosted: Tue Nov 10, 2009 5:39 pm 
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Looks to like the cooling system is operating as it should. You turn the defrost on and the ECT went down. It should, you are drawing the heat from the ECT which in effect is coolint the ECT.

I thought about the HF scanner but Amazon has a better one for a couple dollars cheaper I will most likely get. It will only be used for the Venture since it is our only vehicle at this time, but I expect to get another vehicle in the next 6 mos or sooner (crossing fingers for sooner). I don't have a laptop so the other "toy" won't do me ay good. I forgot to mention, I have been trained and certified as a mechanic (certification in brakes) and have run 2 different shops and worked in countless others. :wink:

Gas mileage as you know is dependant on the operating temp of the engine and if it will be a rich or a lean mixture. Running cooler, I did not notice a huge increase in fuel consumption, but I did notice a slight increase. My vans overhead OBD states my average mpg to be 22.7. What is yours? I figure this to be normal for the type of vehicle it is.

I really think you are pegging too much on the T-stat opening at 195. You can get hotter & cooler T-stats and most cars from the factory are the industry standard 195. As I said, if I were you, based on what I have seen, I wouldn't worry about changing your T-stat. There isn't anything wrong with it.

Putting cardboard in front of the radiator is an old trick. It has helped alot of people, but also has ruined cooling systems. Make sure you do not block off the majority of the radiator. Just use a small piece to start out with. You don't want to block air flow if the fans kick on. a little won't hurt but if all the fans are sucking in is cardboard, they could burn out also. Take a box fan for your house. Turn it on and block the back intake and listen how the fans pitch changes and feel the miniscule amount of air that makes it thru and you'll see what I mean.

When it gets cool here (I live in the boonies) the temp gauge usually doesn't get very much past the 'C' marker. Usually 1 or 2 lines depending on the outside temp.

Good luck with what ever you decide to do. :)


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 Post subject:
PostPosted: Tue Nov 10, 2009 9:43 pm 
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I was really thinking about putting some flexible plastic sheet behind the main opening in the the hood (grill), and not blocking the radiator (or condenser) at all. That way there will be plenty of air flow from "below" and the surrounding area under the hood, but the majority of the air coming from "straight on" will be blocked. If it seems to get too hot, I would either fold the plastic sheet over to allow more air through, or perhaps cut some holes in it.


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 Post subject:
PostPosted: Wed Nov 11, 2009 2:31 pm 
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That'll look like hell but hey, whatever works for ya. :)


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 Post subject:
PostPosted: Mon Nov 16, 2009 3:09 pm 
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I still get 'INVALID' when I press submit when replying. No big deal though. I click back and then the forum header and I find my reply went through.

Would be aggravating if this were a more active forum.


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 Post subject:
PostPosted: Mon Nov 16, 2009 5:04 pm 
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Splicer wrote:
I still get 'INVALID' when I press submit when replying. No big deal though. I click back and then the forum header and I find my reply went through.

Would be aggravating if this were a more active forum.

Hi again,

I am thinking that the server has something messed up. The error log says something about a malformed header, and didn't really change anything in the application layer.

I am actually thinking about migrating to a newer version of the software that drives forum, as that is what is currently supported by the host. But it is not exactly on top of the priority list, since the posting actually works. I will also have to schedule the time to do it and make sure everything transfers properly, and to make sure any of the changes I have made work too.

Thanks for putting up with it!

Take Care,


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 Post subject: Thermostat Changed
PostPosted: Sun Dec 13, 2009 3:10 pm 
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After a long trip back from our Thanksgiving trip, and getting a P0128 code during one of our stops to eat, I finally got around to having the thermostat changed. Guess what? The van now warms up very quickly (about 5 minutes max) and basically STICKS at about 198 degrees on the gauge.

I gathered some data using my capture tool and plotted it out to confirm the results. The only time it went above 200 was when I was parked and let the van idle. Once it was up to temperature, the gauge didn't really drop below 198, except for maybe a couple of degrees.

It has been kind of chilly here the last week or so (down to the high 30s at night), and it has been nice to have the van warm up and pump out some HOT air from the heater vents. Sweet!

I will see if I can generate a data plot similar to the one I did before (on the main site), just to see how they compare.

Take Care,


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 Post subject:
PostPosted: Sun Dec 13, 2009 7:17 pm 
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Glad you finally got it taken care of Greg. It has been 17 degrees here so the cardboard in front of radiator is working well for us. No more codes since the fans don't need to kick on. In my case I think it was just a fluke issue that the relay(s) stayed closed. Electronics are funny things. The OBD in my Venture probably just had glitch.

Merry Christmas! :D


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PostPosted: Thu Oct 06, 2011 12:45 pm 
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Hey guys, I need to replace my thermostat in my 99 Montana. Can anyone offer me some advice? You said it was harder than normal. What us involved in removing and replacing this thing. I have ideas as to where it could be, but I'm not sure. It doesn't look like my 78 Olds. Please help me.


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PostPosted: Thu Oct 06, 2011 2:27 pm 
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I don't think Greg did it but rather had it done. Honestly, I wouldn't do it either, I'd have it done. This is a link to the location:

http://www.my-chevy-venture.com/bleed-valve-thermostat-1.html


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