4.2L Engine Not Getting Up to Temp

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Got an issue here that has been bugging me for the better part of year. I only notice it during the winter times. I have noticed that the coolant will not get up to temp in the winter if I just let it idle in my driveway or use the heater. A typical scenario goes something like this:

A. Start up car in cold weather < 32F.
B. The engine starts normal and the gauge gradually gets up to ~130 and stays there.
C. Drive about 10 minutes with the heater on and the gauge still stays at that temp.
D. Drive another 10 minutes with the heater off and the engine gets to proper temp of ~200F
E. Drive another 5 minutes with the heater on and the temp then falls to about 130 F and heats a bit more but never gets to ~200 F.

Interestingly after all this time has passed driving my vehicle I have no CEL. Just waiting for it to come on but the damn thing is harassing me. I have done all the regular maintenance items and the following below that you would think would be the cause but it has not improved the situation.

1. Changed thermostat and coolant. (1 year ago)
2. Changed Air Temp and Coolant temp sensors (1 month ago)

I am wondering if these warmup characteristics are normal for our vehicles? Kind of looking for a direct comparison to someone who has our vehicle up here in the north. A sort of sanity check. I would think my envoy should heat up to temp no matter what temp it is outside if i let it idle. It seems as thought the thermostat is sticking. Does this sound plausible even if it was changed a year ago? Perhaps my fan is running all the time and i don't know it? The performance of the truck does seem to change at times and kind of leaning towards something that would produce drag on the engine like a bad fan clutch. So any idea how I would prove any of this? Again, no CEL. :confused:

Any insight is appreciated. TIA!
 

navigator

Member
Dec 3, 2011
504
it doesn't get as cold here as there but even when it is in the 20's here my TB is the fastest warming vehicle I have ever driven.
Even if I don't take time to let it warm up, I can crank up get in it and within about 2 miles I am just under 210 with the heat on.

I know I need a Tstat because I don't get to exactly 210.

Is your heat warm, really warm like normal?
My first thought is you got a bad Tstat, I've heard of them being bad when new occasionally.
If your heat isn't pretty warm that would be my guess.
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
navigator said:
it doesn't get as cold here as there but even when it is in the 20's here my TB is the fastest warming vehicle I have ever driven.
Even if I don't take time to let it warm up, I can crank up get in it and within about 2 miles I am just under 210 with the heat on.

I know I need a Tstat because I don't get to exactly 210.

Is your heat warm, really warm like normal?
My first thought is you got a bad Tstat, I've heard of them being bad when new occasionally.
If your heat isn't pretty warm that would be my guess.

Well it was 20 this morning and it definitely didn't heat up that fast. Once its warmed up it feels fine. I am leaning towards a bad tstat as well. I am going to take temp measurements from the radiator neck and see if the temp goes up gradually before the tstat should even open. That should be definitive proof.

Tell me something. Does yours heat up well at idle or does it take a long time?
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Ok! I think I found the issue today. It really isn't an issue at all as it turns out.

I just got an Android smartphone the other day and picked up the Torque app. So I decided to give it a whirl. Basically what I did was I checked the engine temp directly with scan tool and lo and behold my suspicions were confirmed. As it turns out, what I thought was fully warmed up turned out to be wrong. The dash gauge might be reading 210 but the actual temp coming from the scan tool could be as low as 170F! I have confirmed by reading posts on TV (that I somehow missed all this time)that the dash temp gauge is a GM hoax. What was happening is that I was going by the temp gauge on the dash. As some of you know, this gauge reading on the dash is a fabricated lie. It was showing 210F way too soon. So I drove the truck some more today and took readings using the scan tool with the heater off and it works as advertised. It got up to 195F in short time < 5 minutes. Once at 195F I turned on the heater and the dash gauge never moved. The scan tool only went down to 185 F or so and then started to come back up.

Now the reason the temp goes down when idle is due to a two fold issue. 1. I have an XL and the larger coolant capacity for the rear heater core cools down the coolant in the engine about as fast as the engine wants to heat up. So, yeah it won't heat up if I just let it idle with the heater on. I have yet to test if the coolant temp will drop after I let it heat up at idle.

Ok, and now for what I think is the main reason it takes so long for my truck to heat up! 2. My recirculate actuator has not been working for over a year. So this basically means that I am sucking in cold 20F air into my cabin thus cooling off the engine even faster. Seems stupid that I didn't think of that before but...

So it appears everything is fine. Coolant gets up to temp with the heater off. One final step I am going to take is to put a piece of cardboard in front of the grill and see if that helps with the whole heating up the cabin deal. Damn, I really need to get this recirculate actuator fixed.

Kind of feel like a thermostat authority now that I read a whole slew of posts on TV giving me these ideas and things to check. I just knew something wasn't right. As it turns out it was me all along. People use a scan tool before changing the thermostat! You can't go by the dash gauge or any visual sense that it is a tick above or below kind of reasoning. The gauge is controlled by the PCM and displays the reading as dictated by the PCM. The PCM gives the gauge incremental information based on complex algorithms developed at GM that give you BASIC information and is not degree accurate.
 

DocBrown

Member
Dec 8, 2011
501
Captain, I disagree. The gauge works fine. The guage must read 210, or just below and "kissing" the 210 marker. Any lower and its running too cool. Many owners have said pretty much the same thing on the OS. Mine read a bit below 210 for a while and I ignored it thinking the same as you that its just an idiot gauge. I ended up having to replace my catalytic convertor. I have an EXT and the temp gets to just under 210 and stays there. It heats up fairly fast and I never see the dramatic fluctuations you are seeing. DO NOT put cardboard in front of your radiator. That's a old band aid to get heat out of a car with a bad cooling system. The extra stress put on the clutch fan by trying suck in air that isn't there is going to cause other unwanted trouble. In the old days it was not unheard of to have a fan blade stress to the point of breaking and tearing up the radiator.

I think you're making this harder than it needs to be. The behavior your describing sounds like low coolant level. Check your fluid level first. Not just the reservoir. Open the cap when its cold and make sure its full. Change the thermostat. Its not that hard, take your time. Its easiest if you take off the alternator. A flush and fill probably wouldn't hurt either.
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
DocBrown said:
Captain, I disagree. The gauge works fine. The guage must read 210, or just below and "kissing" the 210 marker.

Couldn't disagree more. Being a fellow engineer I totally agree with Roadie and what he said regarding the way the dash temp gauge reports coolant temp. It's a total fabrication.

DocBrown said:
The behavior your describing sounds like low coolant level. Check your fluid level first. Not just the reservoir. Open the cap when its cold and make sure its full. Change the thermostat. Its not that hard, take your time. Its easiest if you take off the alternator. A flush and fill probably wouldn't hurt either.

Right. That's the first thing I checked. I am not as green of a mechanic as I may come across. I have over 20 years of experience working on cars and over 1000 posts over on TV. My inquiry to this issue stems from a curiosity of how our systems work from a component level. And being the perfectionist that I am I expected to see an exact representation of the temp on my dash guage as reported by the coolant temp sensor. I am not saying that the dash gauge is completely in error from a programming perspective. However the PCM buffers it so that the customer doesn't get paranoid about normal swings in temp over a discrete period of time. It helps calm the customers nerves and results in less trips to the dealer or mechanic from aggravation. I am sure the reason they made the systems the way they did is due to the nature of the engine coolant system and how it works.

I am going to chalk this anomaly up to a case of GM engineers working along side of customer relations too much. I would have preferred an unbuffered dash reading being an engineer.
 

Iahawkeye

Member
Jan 24, 2012
52
I have had the same problem for years. I am a firm believer that a few minutes of idling when really cold is well worth the prevention of bad things happening with cold metal parts. Now, with that said, I have noticed that according to the gauge, the envoy never reaches 210 while idling. In fact, I noticed once on a really cold day, (1 F) that after reaching operating temp, and then sitting in a parking lot waiting for my wife, the temp went back down 2 or 3 notches below normal. I have put in 3 thermostats since i have owned this (4 yrs) and it has never changed. I am inclined to agree with captainxl and that it is a large system with the added rear heater core and an imperfect gauge are the culprits.

I am intrigued, though, about the broken recirculation valve that you mentioned. Where would i find this? Thanks.
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Iahawkeye said:
I am intrigued, though, about the broken recirculation valve that you mentioned. Where would i find this? Thanks.

I would start with a new thread about the air recirculation actuator. Might get more attention. Perhaps Roadie has some of these pics and can put them over here.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
I noticed the same thing yesterday.

Went to pick up a neighbor to take to the airport. The Envoy never got more than 2 marks below the 210 mark while parked with the heater blowing.

I wish I'd turned the blower OFF, just to see if it had any affect on the temp.
 

Chickenhawk

Member
Dec 6, 2011
782
I think you are confusing the oil pressure gauge with the coolant temperature gauge.

Oil pressure is a fabricated reading, generated by the PCM.

Coolant temperature is a direct reading from the coolant temperature sensor. It reads reasonably accurately, and if the needle is a couple of ticks to the left, the thermostat and/or coolant temp sensor will need replacing.

What we have found by comparing temp gauge readings with scan tool readouts is that the gauge is not linear, in that a couple of ticks to the left is a LARGE drop in temperature. This is precisely why we tell owners again and again that if the gauge is not straight up when warm (or a tick to the right) then something is wrong.

If the coolant gauge was a fabricated number, we could not tell owners this ... and I can't remember the last time experienced folks like the Roadie, and the many others who diagnose thermostat problems by the position of the gauge needle, were wrong.
 

DJones

Member
Jan 21, 2012
701
St. Petersburg, Florida
Chickenhawk said:
What we have found by comparing temp gauge readings with scan tool readouts is that the gauge is not linear.
Canadians have to figure out the hard way that it is not linear. Our US gauges have 100-210-260, so anyone can see that it isn't linear.
 

HTUSA

Member
Dec 28, 2011
34
I live here in TN and my temp on the TB never goes above 200degrees.
I use a OBD2 bluetooth and the Torque App.

I wonder if I need to change my thermostat.
Cars have become way to complicated over the years with too many sensors etc...
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Chickenhawk said:
What we have found by comparing temp gauge readings with scan tool readouts is that the gauge is not linear, in that a couple of ticks to the left is a LARGE drop in temperature. This is precisely why we tell owners again and again that if the gauge is not straight up when warm (or a tick to the right) then something is wrong.
I think there are two things going on in the PCM's gauge display. And we should be careful to separate the two for a precise discussion.

The gauge is non-linear, but the designers took Ergonomics 101, and decided that straight-up 12 o'clock is a position that makes it easy for the average non-enthusiast driver to scan (if they EVER scan their gauges) and see that all's well. In general, one or two needle WIDTHS to the left of 12 o'clock is a cause for concern. One or two tick marks is a HUGE drop in temp. Looking at the OBDII data, my needle stays straight up and doesn't move when the real sensor-based data reads from 190-214 or so.

The gauge data is also filtered and averaged, so short-term changes don't wiggle the needle, such as when you're going down a short hill and your coolant drops to 175-180 degrees for a short time. The non-enthusiast driver (my code phrase for Ma and Pa Kettle - see below) gets alarmed when they see temperature gauges move around, so the designers smoothed out the data and don't present the truth to the N. E. D. Oddly enough, the designers decided the N. E. D. NEEDS to be reassured that their oil pressure goes up a bit with RPM, so they LIE and fabricate the data for moving the oil pressure gauge. They must have profiled the N. E. D. as nervous, but not entirely stupid. Rather insulting to the enthusiast drivers in the crowd, which is essentially ALL of us here. :wink:

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The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
HTUSA said:
Cars have become way to complicated over the years with too many sensors etc...
But the fuel economy and efficiency is vastly improved. Personally, I do *not* want to go back to the days of 92 vacuum hoses running all over the vehicle, any one of which could leak and kill your mixture. Points? Condenser? Distributor rotors? Plug wires? Centrifugal and vacuum advance? Idle and normal jets? Carb floats? Synchronizing a 4-barrel? Changing plugs every 20K? Ick. :no:
 

HTUSA

Member
Dec 28, 2011
34
the roadie said:
But the fuel economy and efficiency is vastly improved. Personally, I do *not* want to go back to the days of 92 vacuum hoses running all over the vehicle, any one of which could leak and kill your mixture. Points? Condenser? Distributor rotors? Plug wires? Centrifugal and vacuum advance? Idle and normal jets? Carb floats? Synchronizing a 4-barrel? Changing plugs every 20K? Ick. :no:

This is true.
 

asautt

Member
Dec 5, 2011
40
the roadie said:
But the fuel economy and efficiency is vastly improved. Personally, I do *not* want to go back to the days of 92 vacuum hoses running all over the vehicle, any one of which could leak and kill your mixture. Points? Condenser? Distributor rotors? Plug wires? Centrifugal and vacuum advance? Idle and normal jets? Carb floats? Synchronizing a 4-barrel? Changing plugs every 20K? Ick. :no:

But Roadie, don't you at least want to return to the glorious days of yesteryear with vent windows and the headlight dimmer switch down on the floor where it belongs?! :biggrin:

Alan
 

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