[dgoodsy]

Hi all,
Some of you will have seen and contributed to a few of the troubleshooting threads I have made while getting this truck to a state that I feel like I can count on it, thanks for all your help so far! I figure I should start a thread/log here to keep track of repairs/maintenance that I do to my truck, just to have all the info in one spot.

Just to give a brief rundown of the history of the truck while in my possession:

Purchased the truck on May 23 2022 with 213000kms on the odometer. The previous owner claimed to have had recently replaced the spark plugs, the tie rod ball joints, and fuel tank vent valve.

I drove the truck home 300km (towing 24ft fifth wheel that we purchased as a package with the truck). On the drive home the truck had issues running warm, but drove and ran well apart from an episode of stalling 3 times trying to cross a highway. When I say “running warm” I mean it got hot enough to give me a dash warning, but after that I slowed down and removed the chrome grill cover and was able to keep it around 105°C for the rest of the trip.

Once it was home and cooled off I was able to check the coolant level. From the outside of the overflow tank it looked full, but it was just scale that I could see, the tank was empty and it took about 2-1/2 quarts to get to the full line. After a flush, thermostat change and refill with fresh dex-cool the cooling system is better, but still a bit flakey. For the most part it stays at the temp it should, but I had a 20 minute period of it running warmer than it should while towing the camper this past weekend (again, I was able to keep it around 105°C), and then again yesterday it ran cooler than it should while on the highway. I suspect it is the (new) thermostat sticking and have a new GM one ordered and on the way. I also have a new fan clutch ordered as well (GM part), I don’t suspect it as the source of the cooling temp issues, but I believe the one on the truck is on its way out.

Also while I was daily driving the truck for the first few weeks it began to give me running/idling issues. For the most part it would just idle really slow, and would eventually stall. For the most part it would restart right away, and was easy to keep from stalling by blipping the throttle. In only one of these events it was very hard to restart, and would immediately stall regardless of throttle input, but it smartened up on about attempt #6 and drove 5 minutes home without further issue. Through these issues I got codes P0100, P0101, P0102, P0154, P0156. I also had code P02254 previous to these running issues (but no CEL with it). I have replaced the MAF, cleaned the throttle body (it was already real clean), tightened intake manifold mount bolts and haven’t had an issue since.

Just for reverence, here are links to my other threads I started for troubleshooting the issues with the truck:

04 sierra 2500 6.0 intermittent rough running

Hi all, I'm obviously new here, and new to gm trucks, but have experience working on my own cars and am somewhat handy with tools. I just bought a 2004 sierra 2500 6.0 4x4 (213000kms/132000mi) a few weeks ago and am having some issues with it. It seems strange because there seem to be 3...

www.silveradosierra.com

2004 sierra 2500 6.0 - weird cooling issue

Hi All, I purchased the truck about a month ago – 2004 sierra 2500 6.0, 213000kms/132000mi. It was a truck and trailer (24’ fifth wheel) package, I had issues with it running warmer than it should have the day I brought it home but I found the coolant was low, and thought that was the problem...

www.silveradosierra.com

 

[dgoodsy]

Trailer plug repair

I had an issue with the trailer brakes not working. Started troubleshooting with the brake controller in the truck – a tekonsha voyager. I found that the ground and batt+ wires going to the controller tested good. The brake output signal had 12v all the time at the wire splice right behind the controller, however the blade in the connector at the back of the truck had about 0.2V. So I had at least 2 problems – the controller was bad and somewhere between the controller and the plug there was a break/poor connection. I pulled the connecter apart enough to peek inside and sure enough it was full of moist junk. I picked up a Tekonsha P3 to replace the voyager, and picked up the same Reese vehicle end connector. I wired them both in and now the braking signal can be modulated as it is supposed to, and have proper voltage at that pin in the rear connector too.

The Reese connector has a gasket of sorts where the wires go in the back of the plug, but it really doesn’t do anything to seal the openings between the individual wires as they com in the back of the connector. My bet is this is what let in all the dust and moisture, which helped turn the brake signal wire (buried in said moisture/junk at the bottom of the plug) into blue powder. That entire terminal on the back side of the plug was gone, I couldn’t even find the screw. When I installed the new one I used a sealant to seal out any moisture/dust from getting in between wires, and around the body of the plug, hopefully that will help this connector last longer.

In testing the connector to make sure I had all the wires in the right spot I found that all was good except the batt+ wire. In searching the internet I found it is supplied by the “Stud 1” – I checked mine and it is blown. I will pick up a new one and a few spares, hopefully that solves the issue. The truck was hooked up to the trailer while the trailer had no batteries installed and its battery leads were dangling in the battery compartment – I’m hopeful the blown fuse is a result of that + battery terminal grounding itself out, and not an issue with the wiring in the truck.

 

[dgoodsy]

Starter replaced at 214260 km.

Lately the starter has been warning me that it isn't quite right. It seemed heat soak related - sometimes when I would get it up to temp on warm a day, then shut it off for anywhere from 10 mins-1 hour, it would struggle. By that I mean that it would spin without engaging the starter gear in the flywheel. Usually on the 2nd or 3rd try starting it would actually engage and start the engine. It seemed to be getting somewhat frequent so I ordered a starter (AC Delco) among other things from rockauto. I got a chance to install it last night. Pretty easy job for a starter replacement I thought, almost spent as much time trying to figure out if I needed to deal with the radio code because of disconnecting the battery as I did actually replacing the starter. With the new starter in the engine spins noticeably faster when starting, and I never thought the old one spun slow, hopefully that will help it to start well come wintertime.

To follow up from the last post, I replaced the fuse for stud 1 and now have 12V batt+ to the trailer plug. I ended up replacing the connector on the trailer side as well, and now lights and what not work in the trailer without the trailer battery connected, so everything seems to be good with the trailer wiring in the truck and trailer.

The "stud 1" fuse isn't labeled on the fuse box diagram as far as amperage, but the one I took out was a 30 amp, so I put a 30 amp fuse back it. Is that the appropriate/max for that slot? The internet tells me mostly 40, but sometimes 30 or 50 amp..

 

[dgoodsy]

Replaced thermostat, fan clutch and oil pressure sensor at 214282kms.

As I mentioned earlier I had done a flush of the coolant system, and fresh fill with dexcool, replacing the thermostat while I had the system open. The cooling system worked better which was to be expected, but still had some worrying events while towing the trailer - for one stretch of about 20-30kms during a 500km round trip the coolant temp was really unsteady and slightly warmer than it should have been. Then on another highway drive later in the week it struggled to get up to temp, much longer than it should have. I suspected the new thermostat I put in wasn't working right (part store special - "cooling depot"/motorad brand) so I ordered a new AC Delco one from rock auto, as well as fan clutch, oil pressure sensor and other odds and ends.
I drained the coolant again, saving as much as I could. (thanks again gm for taking away the rad petcock...) I ended up siphoning out as much as I could which made it much easier to save the coolant without contaminating it with the dirt and grime in the engine bay. When I got the old thermostat out I inspected it and found scratch marks all around the copper slide tube (?) - this makes me almost certain that it was sticking and causing my issues.

I installed the new gm thermostat, as well as the new gm fan clutch, and refilled with coolant. I won't feel 100% confident that these new parts fixed my issues until I tow the trailer with no more "symptoms" for a few more trips, but I am pretty confidant at this point.

I also replaced the oil pressure sensor while I was under the hood. With the old one the gauge was always pegged at max pressure. The gauge reads what I would expect now, with the new one installed.

While I had the old fan and clutch out of the truck I noticed the AC belt is on its last leg. I will replaced that one very soon, and will do the main serpentine belt while I am at it.

I also purchased some new engine oil and filter for the truck, I plan to change oil in the truck before towing again. The window sticker says I have 3000kms left in this oil, but I want to change it just in case I compromised it when towing with elevated coolant temps.

 

[dgoodsy]

The truck started to make a squealing sound yesterday. It only does it at idle when it is cold started, then after a minute or so it only squeals from just above idle to ~2000 rpms. I didn't have much time to look at it yesterday, and now on my way to work this morning the check engine light was on for code P0446 (EVAP vent control circuit). Any chance it is related to the squealing? I haven't had it myself but have read that vacuum leaks can sometimes squeal.

I'm hoping tonight I can remove the serpentine belt to see if it is something in the accessory drive squealing. I spun all the pulleys/idlers while I had the belt/fan/clutch removed and everything spun really nice, so I don't expect it to be anything with the accessory drive, but I've been surprised before.

 

[dgoodsy]

Oil change - at 214,305kms

I spent a very little bit of time trying figure out my squeal last night - it is actually more like a really fast squeak and the frequency of the squeak seems to follow the engine speed. I tried to count the squeaks and it seams like it is about 50-52 squeaks per 10 seconds at idle (650 rpm). If that's accurate that would be about 300 squeaks/minute. I had done some reading that cam lobes/lifters can squeak when they are on their way out so I was eager to (hopefully) rule that out.
(reading stuff on the internet while diagnosing a vehicle issue can be like looking at wedMD sometimes…)

I removed the belt and when I started the engine (very briefly - 10 seconds or so) and there was no squeak. I put the belt back on and the squeak returned, although it seemed to be a little quieter. So that made me feel a bit relieved, although I'm not sure how I'm going to go about diagnosing what exactly is causing it. As I mentioned previously none of the belt driven components/tensioners/idlers show any roughness, looseness or noise when spun by hand. It seems that whatever it is will have to be spun faster than it spins at idle so I will need to find a way to do that, and hopefully the culprit will show itself without the load of the belt.

While I had the truck in the garage I changed the oil and filter - I used supertech synthetic 5w40 and Fram XG3506. I don't know what most people around here use for oil but given that I plan to change 2x per year - (5w30 in winter, 5w40 in summer/towing season) I'm not worried about using an oil that isn't the best/fanciest oil out there.

 

[RedSLEd]

Just a guess, but I'd be looking at the water pump or belt tensioner. Keep us posted.

 

[dgoodsy]

Yes I was hoping it wasn't the waterpump, but it would be just my luck. When replacing the coolant, thermostat and fan clutch I thought about doing the pump too since they don't last forever, but opted not to. I'm hoping not to drop the coolant again..

That being said after last night I have reason to think it is just the belt itself. I ran the belt against a piece of was and the squeal went away temporarily. My new belts should arrive today, I will put them on and hopefully that's the last of the squeaking.

 

[dgoodsy]

Changed Main serpentine belt and AC belt - 214,320kms

On Friday Jul 8 I got the belts changed. The AC needed to be changed because it was starting to spit off chucks of belt. The main belt looked fine but I decided to change anyways while I did the AC belt, so I ordered AC Delco belts for both. After they were replaced I now have confidence that the AC won't suddenly quit on me, and the squeaking is gone, so I'm happy with that.

I am less happy with the cooling system. We towed our boat (3000lbs with trailer) to the lake on Saturday, it was a hot day by most of Saskatchewan standards (31C/88F), and when climbing the "large" hill on the way to and from the lake the coolant temp climbed to 106C /223F, up from 93C/200F when cruising on flat road.the climb im sure eould be less that a minute long at 70mph, it seemed like the temp would have kept climbing if the hill was longer. Then when I was booking the boat into the garage and unhooking (idle or very slow moving for about 10 mins, AC on) the temp climbed again to 106, and seemed like it was still climbing. It doesn't seem right to me that it can't keep itself cool with relatively light towing/climbing, or idling, given that: the weather wasn't that hot compared to lots of other places, the the cooling system has been flushed, and fresh coolant put in, the rad was just washed out pretty good (the outside of the rad - on friday), the thermostat and fan clutch are new. I'm inclined to thick the idle problem isn't an issue with the fan clutch as the ac seemed to be working decent.

Maybe I'm overanalizing it, and when loaded the engine gets up to get up to that temp before the reaction of the thermostat opening is seen in the coolant temp stabilizing and maybe dropping back down?

Another temp question as a towing noob - the trans fluid temp was at 74C/165F when towing on the highway, and at 85C/185F when towing back in the city - is this normal for it to be warmer when stopping/starting/ slow speed? I assume so due to the unlocked converter and less airflow through the cooling stack, but just checking.

Thanks for reading and for the input.

 

[RedSLEd]

Just FYI, my dash gauge shows about 210*F on my truck. My scanner shows it's really at 192*F. I would put a scanner on your truck to verify the actual temps instead of relying on the dash. You're probably fine.

Any time the trans is working harder (stop-n-go traffic, hills, towing) it's going to be warmer. 185*F is perfectly fine no matter what. You can figure ambient air temps plus 100*F is 'normal'. How's the fluid condition/age?

 

[dgoodsy]

Just FYI, my dash gauge shows about 210*F on my truck. My scanner shows it's really at 192*F. I would put a scanner on your truck to verify the actual temps instead of relying on the dash. You're probably fine.

Any time the trans is working harder (stop-n-go traffic, hills, towing) it's going to be warmer. 185*F is perfectly fine no matter what. You can figure ambient air temps plus 100*F is 'normal'. How's the fluid condition/age?

The coolant and trans temps I stated are from the OBD2 reader/torque app. My guage matches the torque reported temp pretty closely too im finding.

I know 185F is just fine, but that was with a small ski boat in tow. I am curious to see what they will be in town and on the highway with the camper trailer in tow - well over 2x the weight and significantly more wind drag. Will find out this week as I will be taking it on a trip leaving this Wednesday. Will be keeping a close eye on trans and coolant temps for sure. I'm hoping not to spend money on a cooler upgrade if it really isn't required for this truck/trailer combo.

As far as trans fluid age and condition - unknown. I intend to replace it, but haven't had the opportunity yet. What comes out on the dipstick doesn't look or smell alarming, but I still want to change it. I'm currently waffling if I want to open a cooler line and "flush"/replace all the fluid at once, or just drain the pan and top up a 2 or 3 times over the next 6 months/year.

 

[silentbravo]

I would say 30A fuse for your tow plug circuit is max, GM definitely didn't run bigger than 10AWG wire back to that plug.

How are you monitoring the coolant and trans temps? Just by gauges on dash or via OBD. The gauges are kind of lazy, so you can expect up to 10 or 15F degrees variations one way or the other from what gauges show.

It's best to monitor directly from the computer via OBD port.

Your trans temps are great, and your guess as to why/when it heats up looks valid to me. Unlocked converter is building heat.

What temperature was the thermostat you put in?

 

[dgoodsy]

I would say 30A fuse for your tow plug circuit is max, GM definitely didn't run bigger than 10AWG wire back to that plug.

How are you monitoring the coolant and trans temps? Just by gauges on dash or via OBD. The gauges are kind of lazy, so you can expect up to 10 or 15F degrees variations one way or the other from what gauges show.

It's best to monitor directly from the computer via OBD port.

Your trans temps are great, and your guess as to why/when it heats up looks valid to me. Unlocked converter is building heat.

What temperature was the thermostat you put in?

Thanks silentbravo,

I will leave the 30 amp fuse in there.

All the temps I am quoting here are read from my OBD port via the torque app.

The trans temps looked okay to me when towing the boat, but I didn't expect anything else really as it isn't a heavy boat, or a hard pull.

Both thermostats I have put in have been 86C/187F.

 

[dgoodsy]

We took the truck and 5th wheel on a trip this past week, about 500kms round trip. I had mostly used the gauges rather than the torque app to watch trans temps when towing the 5th wheel previously, so I planned to use the torque app this trip to try and get a feel for what is normal for the truck, and to see if I should be considering an upgrading the trans cooler on the truck (i really don't want to if it isn't necessary). I came away with a somewhat interesting observation.

To simplify what I noticed – the truck will downshift into 2nd gear for certain grades. Usually the truck will stay in 2nd, 3800-4000rpms even if the grade levels out somewhat. I can “help” it upshift to 3rd in these scenarios and it will pull the rest of the hill in 3rd just fine. If I let it climb in 2nd the trans temp heats up (not a surprise as the torque converter is not locked in 2nd) but the coolant temp does too – I saw coolant temp get to 105C/221F which isn’t alarming itself, but it was still climbing when the trans finally upshifted on its own to 3rd. If I help it shift to 3rd on the exact same grade then the coolant will stay (or fall back to) between 93 and 95C/199-203F. My question – is:

1) the rising coolant temp simply a result of the hotter trans fluid going through the rad,
2) or is something else going not right with the cooling system that it doesn’t cool well at 3800+ rpm?

My inclination is 2), but I’m not sure what would cause it - a cavitating water pump? I think this water pump is original, is cavitation a problem once the pump ages a bit?

For this 5th wheel it isn't a huge issue as I can sort of override the issue and make it upshift to 3rd but I may be pulling a heavier load on the same route and have concerns if the truck does need to be in 2nd gear for longer periods of time.

 

[silentbravo]

You didn't post your ambient temp for the trip but it doesn't sound like anything abnormal was going on. If the trans is heating up, the trans cooler, which is at the front of the cooling stack, will be dumping extra heat into everything behind it.

As for the radiator pass through, that may help or hurt depending on trans temp also.

Running at 3k+ RPM for extended periods and with heavy load builds a lot of heat, now whether it would keep climbing and run out of control is hard to say.

I took my truck on a 500+ mile round trip yesterday to pick up a truck, lots of hills and grades throughout. The biggest was returning home, 7% grade about 8 miles long. Trailer I guess was about 5-6k lbs, ambient temp started at upper 90s F. and was down to 80F by the top.

I could only pull about 40-45mph, kept it at 3k RPM. I did turn off A/C for this hill, max temp got to 234F ECT that I saw. Trans probably just touched 200F or maybe slightly below.

Now I upgraded my trans cooler to a huge one, and it almost never runs over 160F now
This was not quite worse case scenario for a tow trip but the truck did just fine as far as I'm concerned.

I actually never noticed my truck ECT get that warm ever before, but most of my previous towing is a light boat or in cooler weather. I'm pretty sure my trans cooler was dumping tons of heat, so that probably didn't help everything behind it.

I also changed to electric fans, which work well but in high temp, heavy load towing, mechanical fans going to win for sure. So I may be slightly handicapped there.

 

[dgoodsy]

Thanks for the reference points silentbravo.

The ambient temp was about 30C/85F. The trailer is a 24ft 5th wheel, I expect it is about 7500lbs loaded.

The "big" hill I am referencing is a 6% grade, 1.5km long. At the top my ECT was 108C/226F and TFT was 98C / 208F. both ECT and TFT rose 15C/26F in a 1 minute climb, and hadn't noticeably slowed down when I reached the top of the climb. I feel could help keep the temps from climbing so much by slowing down 15 km/h or so but if something is not working right with the cooling system I want to address it. The thing that worries me is that the behaviour isn't a whole lot different when pulling slight grades in 2nd. For reference there have been a number of much longer hills where I could barely tell we were climbing, and when in 2nd gear the ECT and TFT rise, but not quite as fast. One such hill i observed until ECT was at 105C, then I encouraged it to shift into 3rd. Then while maintaining the same speed on the same grade the ECT dropped to 95C in 2 minutes or less.

maybe I am being nitpicky about temps, but it doesn't seem right to me.

edit: The fact that I saw ECT climb to 106C+ when idling (with AC on, ~30C/85F ambient) just makes me more convinced that something isn't right. Again ECT it was still climbing until I drove the truck around the block, which cooled it down.

 

[silentbravo]

Does your engine fan get much louder when it is really hot, say 100C or higher? By that temp or maybe even sooner the engine clutch fan should be locked solid and be quite loud, noticeable in the cab even unless you have terrible loud exhaust like mine lol.

How fast does the truck cool down once you crest a hill and remove most of the load? After my long grade It was a pretty steep hill down which I was coasting and engine shed heat super fast. It actually dropped about 30 degrees by the time I got back down and had to use throttle again. From 232F to 198F I saw.

Have you ever cleaned your radiator or A/C condenser from bugs/dirt? Mine was plugged up pretty good last year, I hadn't cleaned since I bought the truck in like 25k miles so that probably wasn't helping my previous towing adventures.

You are using Tow/Haul mode or no?

 

[dgoodsy]

I guess I can't say honestly that I have listened specifically for the fan clutch in these scenarios when it is getting hot. I know I have heard it lock up at cooler temps though - probably around 95C/203F. 3800 rpms is pretty loud even with the factory exhaust, but I'm thinking I should still be able to hear the fan if it does lock up at 3800 rpm. I will pay attention to this next time out.

It seems to cool down fairly quick to me. If coasting it probably takes 2 minutes to drop down from 100C+/212F+ back down to 95C/203F. And if I get it to shift to 3rd but its still pulling a grade and working it may take 4 or 5 minutes to drop the same amount. I haven't actually timed it, but it certainly is not like it takes 10 mins to shed 10C/18F even when working.

I cleaned out the rad as well as I could the the Saturday before we left on the most recent trip. I removed both the top and bottom fan shrouds and fan/clutch to access the back of rad, as well as unbolted the rad and tipped it back so i sort of had access to the front of the rad. I know it isn't perfectly clean, but I would say it is clean compared to a vast majority of trucks on the road. It really wasn't terrible before I washed it out either.

Yes I use tow/haul mode (though I sometimes get a few blocks down the road before I remember to turn it on) - I assume that's why it holds 2nd gear for so long before it shifts up to 3rd.

I am contemplating holding the truck in 2nd gear at 3800rpms with no trailer on and see if it still heats up. If it does then i will be more convinced that something isn't quite right.

 

[dgoodsy]

I should also add that I wonder if I have all the air bubbles out of the cooling system. The few times I have filled with coolant I have had the front wheels up on blocks, ~7” tall. I add coolant to the overflow tank until there is a few inches in the bottom, then start the truck. Keep adding as the truck burps the air out, to maintain a few inches of coolant in the overflow tank. Once it has finished burping at idle, I rev it to 2500rpms and hold it there briefly a few times. Then I add more coolant to the warm full line on the overflow tank. After it has fully warmed up and cooled down again, I top up one more time and the level in the overflow tank seems to be stable at that point.

I thought this worked well, but maybe it doesn’t get all the air out, and its only evident in the scenarios above? (towing in 2nd gear and hot idle with ac on)

 

[silentbravo]

I haven't had a problem bleeding air on these trucks. Don't have to do anything special really, your method sounds fine.