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2018 Duramax Coolant Temp?

4thDmax

By 4thDmax
in Troubleshooting & Recalls

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4thDmax Enthusiast

4thDmax

Posted
Posted

I'm trying to diagnose a slow coolant leak and the service department can't find it. We get the occasional weak whiff of coolant in the cab and the reservoir is slowly being drawn down. Every couple hundred miles=1/2" of coolant loss. There is no noticeable leak and the service department pressurized the system with no obvious leaks.

 

I have the digital gauges and my coolant temp bounces around quite a bit. Usually it's pegged at 210 degrees but will bounce back and forth between 190-210 at times. Does your Duramax temp vary or does it stay constant at 210? All of my previous Duramax's held steady after they reached operating temp. I'm wondering if I have a thermostat problem and they're unwilling to change it without definitive proof.

 

Thanks!

 

-2018 GMC Sierra Denali 2500HD

phfkef Enthusiast

phfkef

Posted
Posted

If the leak test was done properly, your slow leak must be somewhere between the radiator and your coolant reservoir ( or the reservoir itself).
If your hose connections can be tightened I would do so.
What is the cost of a new radiator cap? Might replace that too.

Sent from my Moto G (5) Plus using Tapatalk

  • Like 1
newdude Senior Enthusiast

newdude

Posted
Posted (edited)

Couple possible leaks on L5P 2017-2019.

 

#18-NA-006: Constant or Intermittent Low Coolant Message Displayed On the Drivers Information Center (DIC) - (Sep 24, 2019)

 

And

 

PIP5487C: 6.6L L5P Duramax Coolant Leaks - (Aug 1, 2018)

 

- Coolant reservoir.

- EGR Cooler

- Coolant pipes

- Engine Oil Cooler - Flywheel Housing Interface

- Behind Starter Motor

 

There is a procedure for checking system pressures.  If during the test it spikes over 25psi or maintains more than 15psi after a 24 hour cold soak, inspect for a bad head gasket. 

 

The best thing perhaps for your dealer to chase would be to dump some of the GM coolant leak dye in there, have you drive it and then let them blacklight the SOB to see where its coming from.  The operating temperature sounds normal however as the two thermostats are 180F and 185F.  That bulletin mentions operating temp of 212F.        

Edited by newdude
4thDmax Enthusiast

4thDmax

Posted
  • Author
Posted
1 hour ago, newdude said:

Couple possible leaks on L5P 2017-2019.

 

#18-NA-006: Constant or Intermittent Low Coolant Message Displayed On the Drivers Information Center (DIC) - (Sep 24, 2019)

 

And

 

PIP5487C: 6.6L L5P Duramax Coolant Leaks - (Aug 1, 2018)

 

- Coolant reservoir.

- EGR Cooler

- Coolant pipes

- Engine Oil Cooler - Flywheel Housing Interface

- Behind Starter Motor

 

There is a procedure for checking system pressures.  If during the test it spikes over 25psi or maintains more than 15psi after a 24 hour cold soak, inspect for a bad head gasket. 

 

The best thing perhaps for your dealer to chase would be to dump some of the GM coolant leak dye in there, have you drive it and then let them blacklight the SOB to see where its coming from.  The operating temperature sounds normal however as the two thermostats are 180F and 185F.  That bulletin mentions operating temp of 212F.        

Thanks. They put some dye in it and I’m going to drive it for a while. 

redwngr Senior Enthusiast

redwngr

Posted
Posted (edited)

There are two thermostats (one opens before the other)

 

My 18 runs a 200 once it is warmed up, same as my LML did. 

 

Most noticeable in cool ambient temps, light loads and hasn't run long enough to be fully temp stabilized the needle will 'wiggle' a few degrees some around the 200*F point.  

 

 

 If it needs 1/2" of coolant every couple 100 miles, the leak should be tracked down.

Sounds like you've got that process started. Let us know the results. 

 

 

 

Edited by redwngr
  • 4 years later...
mfsanford New Member

mfsanford

Posted
Posted

 Sorry to revive this thread. I have a 2018 with 34k miles. Got the low coolant light today. Truck has been sitting undriven in garage for four months. Surge (top tank) full. Ambient temp in Minnesota is 52F. Gauge shows temp at 210 all the time this AM. Wiggled surge tank and warning went off. Assume faulty coolant switch? Still 210 seems high right?

 

Thanks!

newdude Senior Enthusiast

newdude

Posted
Posted
On 5/4/2024 at 11:21 AM, mfsanford said:

 Sorry to revive this thread. I have a 2018 with 34k miles. Got the low coolant light today. Truck has been sitting undriven in garage for four months. Surge (top tank) full. Ambient temp in Minnesota is 52F. Gauge shows temp at 210 all the time this AM. Wiggled surge tank and warning went off. Assume faulty coolant switch? Still 210 seems high right?

 

Thanks!

 

 

Yes.  Needs the coolant reservoir. 

 

As for coolant temp, reading at 210F is probably normal as the gauges don't display an exact readout.  The thermostats in the L5P open at 180F and 185F (one of each thermostat) so to get the most accurate readout you need a code reader that shows live sensor data or something like a Banks iDash to see live coolant temp. 

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