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Discussion Starter · #1 ·
Good Morning,

It's been a few years since I've been here, but the truck is doing some bizarre stuff and I'm trying to find a best foot forward. Let me walk you through what happened.

head gaskets done at 156k miles. Heads machined, proper gaskets, new water pump, glow plugs, the works. Currently at 223k miles and has been driven meticulously like a grandpa, haven't even breached 1100 EGTs. During this time coolant would hover at 180 and go to 195 on highway speeds, NEVER reaches 210. When gaskets where done green coolant was used. kept on 3rd tune (+80) until trans was built and then kept between 4 or 5 for highway driving. Truck is a DOG on the highway so every little bit helps. Would always stay at 180 around town while driving.

A month ago I did AC and heater core replacement, did everything myself. Decided to flush out the green coolant because I know we're supposed to use Dex cool in these engines. Since then, coolant has been fluctuating like crazy and I've been losing some too, not a lot but enough to notice. I've been monitoring the upper rad hose on days I drive it and it's been soft for the past month, this morning it was tennis ball type consistency and the res was down a bit, however I tend to fill the res to the line above the seam line of the degas bottle, as I've been told the full line is actually the seam of the degas. Checked front fender liner and there was no drips from the overflow tube.

When I get done driving I can sometimes smell coolant from the front end and I do a complete once over of the engine and the only spot that appears wet is the bleeder screw on the Tstats. When truck was in for inspection the shop said it's probably just missing the copper washer. The bleeder isn't soaked but just a few residual drips. Coolant is still clean within degas bottle. No coolant smell coming from exhaust. Coolant around town is fluctuating a lot from 180 to 200 fairly consistently, if I get a little hard on the skinny pedal it will heat up fairly quickly.

Here's a variable my friend said might be important, I didn't premix the coolant on refill, I put a gallon of coolant, a gallon of water, rinse and repeat until full when I refilled coolant after AC job.

I don't want to jump to conclusions and say head gaskets but it has all the tell tale signs of it, truck is still really pressurized this morning after sitting for 8 hours with some coolant missing. Perhaps it shot out the exhaust while driving, however truck doesn't smoke at all, no black and no white.

Things I plan on trouble shooting:
Replacing this copper washer on the bleeder to see if this maintains coolant capacity. It dropped from that top line, to just above the seam line in the degas bottle which seems like a lot of coolant, I'd find it hard to believe this is hardly weeping out of the bleeder and evaporating in the half hour it takes me to drive home from work.

Slap a new coolant cap on there because a $15 cap is better than a 5k head job.

Because LLY's are problem children I'd rather keep it running cool than at 210 all the time. Any suggestions for a pair of Tstats to replace with? I know there's 2, I tried replacing them 5 years ago with some from pepboys so maybe they're shot already?

Do you think I should drain and refill the coolant, with coolant that's properly mixed rather than mixing through the degas like a big idiot?

Perhaps is there a giant air bubble in the coolant system? I did bleed the system after the AC job so I dont suspect this is the case but I suppose with this CH of a leak on the bleeder screw anything is possible.

Check oil when I get home to see if it's gray and smells of coolant, I'll also recheck the upper rad hose again and see if it's depressurized more, I don't suspect it will but this trucks been doing bizarre things ever since I've owned it.

I drove this truck a total of 2k miles for all of 2020, it's mostly just a show vehicle at this point. I've made a myriad of bad investments with this thing, so I need to keep it on the road for as long as possible, even if it is just a weekend cruiser. However, I'm trying to buy a house now as I've decided to mature a bit since buying this and a head job at the current moment is my lowest priority. I assume if I have bad gaskets I would have seen more tell tale signs before the AC job and these symptoms wouldn't magically appear after a coolant refill.

Any advice is greatly appreciated! I know there is a ton of variables here so thanks for taking the time to read this.
 

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Have you change the thermostats? And if you did did this start occurring shortly after that.
 

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When you removed your green coolant, did you go to all water, then Dexcool mix? or just add Dexcool mix (even though you mixed it in the tank)? When changing coolants, you need to remove ALL the old coolant everywhere, then start with the new coolant. Note that being orange, Dex is not so easy to see once it evaporates.
 

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Discussion Starter · #4 ·
When you removed your green coolant, did you go to all water, then Dexcool mix? or just add Dexcool mix (even though you mixed it in the tank)? When changing coolants, you need to remove ALL the old coolant everywhere, then start with the new coolant. Note that being orange, Dex is not so easy to see once it evaporates.
I used some generic coolant flush from O'Reillys and followed the instructions directly and let a good amount of water flush that out before adding the dex cool.
 

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Changing the cap might make a difference, but usually a bad cap will suck the upper hose flat over night. If you don't flush every bit of the non-Dex coolant out before changing to Dex, (or vice-versa) the old fluid could cause coagulation and plug up things. Also, it is important to make sure you purge ALL the air out of the cooling system before working truck hard or you can create hot spots, especially in the heads.
 

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Discussion Starter · #6 ·
Have you change the thermostats? And if you did did this start occurring shortly after that.
I changed those about 5 years ago. Truck acted normal after they where swapped out. I don't know if going from green coolant to Dex cool after a flush would effect them that much.
 

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Discussion Starter · #7 ·
Changing the cap might make a difference, but usually a bad cap will suck the upper hose flat over night. If you don't flush every bit of the non-Dex coolant out before changing to Dex, (or vice-versa) the old fluid could cause coagulation and plug up things. Also, it is important to make sure you purge ALL the air out of the cooling system before working truck hard or you can create hot spots, especially in the heads.
I have an appointment with a shop tomorrow to have the coolant system looked at, I followed the bleed instructions from a youtube vid. The more I think about this the more I wish I just stuck with the green as I feel this is really the crux of the issue. I probably didn't flush it well enough.
 

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I think AIR in the system is the problem. ALLY CAT gets my vote. Let us know what you find out.

If you have a place where your can put the truck front up on ramps, or a very steep drive even better, run the engine until the thermos open fully, that will help get the air to the top and out.
 

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Discussion Starter · #9 ·
Hey guys, thanks for the replies. Here's a little update on the current situation.

I took it to a shop and they told me they bled tons of air out of the system, this is great news. Got the truck back and drove it a little bit here and there, everytime I'd drive it I'd still lose coolant somewhere or somehow, only this time there was less fluctuation in ECTs.

Having been fed up with this I went to O'Reilly's and got a block combustion leak dye test. I took the cap off and let the truck idle. As it idled the coolant started coming out the overflow tube, I assume this is because I overfilled it last time it puked coolant out and rad hose was really hard and swollen when cold. I took about 20 ounces of coolant out and performed the dye test and nothing changed. I placed a water bottle on my overflow tube to catch any coolant that escaped and drove it hard for about an hour. Came home and had no coolant in the overfill catch bottle. The degas bottle didn't appear to be lower than I left it.

The truck seemed normal but by at 70 mph the ECTs slowly crept to just under 210 which it's hardly ever hit before and that's with 90 degree ambient temp out in Arizona going highway speeds.

retried the combustion leak test and still no dye color changed.

Checked the upper rad hose this morning and the hose was fully sucked in, the coolant line was slightly lower than the cold full line on the degas bottle. Still had my water bottle on the overfill tube and that was still empty. The coolant was up to the cold fill line when I shut it down last night, but with the truck still idling the upper rad hose was soft and squishy right after my test drives. Quick google search said a bad Tstat will suck the rad hose closed, I already placed an order yesterday so I could keep ECTs down so it's nice to have that tiny bit of foresight.

So it perhaps sounds like a mix of 1. Lots of air in the system, 2. My stupidity constantly overflowing the coolant 3. Bad thermostat. Truck is currently sitting at 225k in change and had the thermostats changed 5 years ago at 156k miles with a pepboys brand so I wouldn't be shocked if they failed and this coolant flush and change was the culprit.

There's always still the possibility this is a bad HG and it's just sending coolant out the exhaust but I haven't noticed white smoke or any "sweet" coolant smell coming from exhaust at all.

I ordered some mishimoto cool thermostats 160 and 185 I believe is in the set. once I slap these in I'll be sure to give it some more test drives and come back here to update. Unless all this new info blatantly screams HG issues, this will be my strategy for now. Might even slap a new cap and ECT sensor on there as they're both cheap so why not.

As always thank you for the time and support!
 

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First off your temp gauge is just a idiot gauge. If you get a separate monitor like a scan tool that can read parameters or a banks idash, or edge cts, you will see that when the trucks gauge reads 210 your actual temp will be closer to 186. Putting lower than stock thermostats in will lower your operating temperature it will also increase fuel usage. And may throw other codes because your ecm will be in constant warm up mode.
 

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First off your temp gauge is just a idiot gauge. If you get a separate monitor like a scan tool that can read parameters or a banks idash, or edge cts, you will see that when the trucks gauge reads 210 your actual temp will be closer to 186.
I was pleasantly surprised to experience this recently, as I thought my truck might be running a little warm... but using the BAFX OBD-II scanner (notice this is around $20) I learned my truck's actual operating temp fluctuated between 186-192 when the dash gauge showed 205-210. That BAFX scanner obviously can't read everything that the $300 Edge CTS can, but it has a lot of options -- and for 7% of the price, it's been a great little tool to have for live monitoring and reading/resetting trouble codes.
 

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Discussion Starter · #12 ·
Hey folks here’s another update,

thermostats came in the other day and I swapped those out. Trucks running like it used too. Occasionally on the highway it will still reach 210 on the dummy gauge. I don’t have a way of reading it through the OBD2 port yet but these times of reaching 210 are few and far between. I properly burped and bled the coolant after the Tstats.

when I returned from my 20 minute romp on the highway I noticed coolant was down just a little bit. Upper rad hose was like a tennis ball right after driving. Waited about 5/6 hours and checked again. Coolant has gone down more but rad hose is soft and squishy.

this means it’s gotta be leaking coolant somewhere during operation OR it’s going through the engine and out the exhaust cuz a gasket is bad. I can occasionally smell coolant at idle but only under the hood not from the exhaust. I checked all usual places, water pump was fine, heater core tubes are fine, lower rad hose is fine. Not really sure where else to check. I’ve done some quick googling and saw some hoses around the turbo can leak but those all appear dry.

my coolant catch bottle has not caught any coolant so I know it’s not being burped.

I’m fairly stumped on this one, I don’t want to just call it HGs because it’s passed all previous tests fine but I’m probably just in denial and dreading that big bill again 😩
 

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Whenever I have had to open the cooling system for flushing or pump replacement, it always takes several cycles and miles of driving before the coolant level stabilizes in spite of all efforts to bleed the system. Seems to be common on LLYs for some reason.
 
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Your not getting coolant in catch can. I don't think it's HG. get some die and black light to find leak.
 

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Discussion Starter · #15 ·
Whenever I have had to open the cooling system for flushing or pump replacement, it always takes several cycles and miles of driving before the coolant level stabilizes in spite of all efforts to bleed the system. Seems to be common on LLYs for some reason.
Okay I will keep driving. I was afraid opening and replacing the thermostats was going to restart this whole process. Thank you for the reply!
 

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Discussion Starter · #16 ·
Your not getting coolant in catch can. I don't think it's HG. get some die and black light to find leak.
It’s bizarre because I smell it up front but all the usual places are bone dry. Do I add the dye to the coolant and just let it run and inspect?
 

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If your radiator is leaking, the coolant gets on the fins and when you drive it is either blown off or evaporated. Pretty hard to find these leaks just by looking. I'd keep adding fluid for a while and see if it stabilizes, then if not able to stabilize fill level, radiator shop easiest/best way to find the leak. They do it all the time.
 

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It’s bizarre because I smell it up front but all the usual places are bone dry. Do I add the dye to the coolant and just let it run and inspect?
yes.
 

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I know I'm late to this party, but I'll throw out some of my opinions...
  • My full-cold coolant level is at the seam. I don't care where the line on the plastic is because anything I add just disappears. I would suggest not adding coolant unless the full-cold level drops below the seam (or maybe even 1/4" below).
  • You mentioned the top radiator hose collapsed when cold. Almost certainly a bad cap. One function of the cap is to let air in so the system doesn't get a vacuum.
  • You mentioned a hard top radiator hose with engine was hot. Yes, of course, because the 2nd function of the cap is to pressurize the system up to 15 psi when hot.
  • I wouldn't put in lower temp t-stats, and I would stick with OEM AC/Delco on this. Lower temp t-stats don't fix overheating problems. They just make the engine less efficient when running cooler, and possibly cause other issues if the engine never gets up to normal operating temps.
  • Air in the cooling system is a big issue on these motors after the cooling system has been worked on. But you learned this lesson like most people (the hard way!).
  • I have never heard of anybody who got one of those exhaust-in-coolant tests to work on these diesels. But that's only after following forums for 15 years, so I guess there's still time for one to be reported.
  • As others pointed out, the dash temp gauge is not accurate. Typical for our LLYs (stock) is for it to show just left of center for any real temp from 188-218*F. It also tends to show higher-than-actual below 188*, and lower-than-actual above 218*. A display reporting from the OBDII port is required for a reasonable accurate measurement.
  • If you really are losing coolant and can't find any trace, I like Ron's suggestion about the radiator. There is also a small soft hose to the turbo that's buried, and probably some other possibilities.
 

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Check in the valley, see if there is any coolant there. Also check the heater core connections- could be dripping from there onto the downpipe and burning off so you can't find it but still can smell it. Check behind the fan pulley, the little mother-:mad:er hose that comes off the coolant bypass pipe from the water pump to the t-stat housing- I've fought those before. It really sounds liek you have a small leak up front that is either hardly visible/well hidden or burning off. I don't think its head gaskets since it doesn't sound like its over pressurizing the cooling system and pushing it out and the exhaust doesn't smell sweet
 
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