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Discussion Starter · #1 ·
So I have a 2017 Chevy 2500. With the L5P duramax and 49k miles. I have been losing coolant periodically. So I add it here and there when the overflow tank gets low and I get a “low coolant message”. I notice a small puddle of coolant under the truck more towards the passenger side. So I then popped the hood and noticed my coolant overflow tank was under pressure when I starting unscrewing it. The next day I did all the at home tests for a blown head gasket… but everything seemed okay. The upper rad hose wasn’t as hard as a tennis ball. And I have no coolant in oil and vise versa….so the next day I decided to unscrew the coolant cap so no pressure could build. I drove the truck to operating temp and parked. The next morning I noticed another puddle under my truck.. but there was no pressure on the coolant system to force it out of the overflow…. So any suggestions are appreciated.
 

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Understand that if the engine us warm then the res tank will be under some pressure. As the engine cools the res will lose that pressure. First, are you sure that the coolant leaking is from the over flow on the coolant res. When you add coolant to the res is the engine cool or have been recently running? Dean
 

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Discussion Starter · #3 ·
Understand that if the engine us warm then the res tank will be under some pressure. As the engine cools the res will lose that pressure. First, are you sure that the coolant leaking is from the over flow on the coolant res. When you add coolant to the res is the engine cool or have been recently running? Dean
I understand that. the coolant is escaping from somewhere.I’m not convinced it’s being forced out of the overflow…due to where the coolant puddle is. But I can’t pin point the cause or where exactly it’s leaking from. Because the coolant overflow tube leaks down the exterior of the passenger frame rail.I’m leaning towards a leak elsewhere and not head gasket related. And the coolant leak on my truck drips down from the crossmember under the truck towards the passenger side. Thanks
 

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Discussion Starter · #4 ·
I understand that. the coolant is escaping from somewhere.I’m not convinced it’s being forced out of the overflow…due to where the coolant puddle is. But I can’t pin point the cause or where exactly it’s leaking from. Because the coolant overflow tube leaks down the exterior of the passenger frame rail.I’m leaning towards a leak elsewhere and not head gasket related. And the coolant leak on my truck drips down from the crossmember under the truck towards the passenger side. Thanks
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This is after about 30 min sitting. When I first shut the truck off. The coolant was up near the filler neck of the coolant reservoir. But I did not notice any coming out of overflow tube
I don't have a L5P and don't know where the marks are for a proper level on the coolant res but to me that is way overfilled. My Duramax and most of the closed systems like this that I am familiar with they coolant level when cold should be toward the mid to lower level of that tank. I should be no where near the top. Look for the marks on the tank and confirm this. It may be as simple as overfilling your system. How are your engine temps when running around? D
 

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I don't have a L5P and don't know where the marks are for a proper level on the coolant res but to me that is way overfilled. My Duramax and most of the closed systems like this that I am familiar with they coolant level when cold should be toward the mid to lower level of that tank. I should be no where near the top. Look for the marks on the tank and confirm this. It may be as simple as overfilling your system. How are your engine temps when running around? D
That level is perfectly normal for a L5P the top of radiator is pretty much level with reservoir cap. OP which crossmember are you saying that it is dripping by? The DEF injector cooling lines like to leak a little Ive noticed already.
 

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That level is perfectly normal for a L5P the top of radiator is pretty much level with reservoir cap. OP which crossmember are you saying that it is dripping by? The DEF injector cooling lines like to leak a little Ive noticed already.
I checked my LMM which has the same type of system and the correct level is no where near the top. This is a closed system with the reservoir allowing for expansion and contraction with the heat of the system. Even at full operating temp it should be no where near the cap or overflow. Show me the marks on the side of the tank if what you say is correct.
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Discussion Starter · #9 ·
I checked my LMM which has the same type of system and the correct level is no where near the top. This is a closed system with the reservoir allowing for expansion and contraction with the heat of the system. Even at full operating temp it should be no where near the cap or overflow. Show me the marks on the side of the tank if what you say is correct. View attachment 1092247
If you reference the picture I posted.. the coolant level shouldn’t lower than the top of the arrows
 

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Discussion Starter · #10 ·
I don't have a L5P and don't know where the marks are for a proper level on the coolant res but to me that is way overfilled. My Duramax and most of the closed systems like this that I am familiar with they coolant level when cold should be toward the mid to lower level of that tank. I should be no where near the top. Look for the marks on the tank and confirm this. It may be as simple as overfilling your system. How are your engine temps when running around? D
I have a banks tuner. And it runs around 185. The highest it’s ever been was 191. And that was pulling a 6k pound tractor
 

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Discussion Starter · #11 ·
That level is perfectly normal for a L5P the top of radiator is pretty much level with reservoir cap. OP which crossmember are you saying that it is dripping by? The DEF injector cooling lines like to leak a little Ive noticed already.
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The coolant drips below off the crossmember below the oil pan
 

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If you reference the picture I posted.. the coolant level shouldn’t lower than the top of the arrows
Never got that into what they want for the L5P but to me the top of the arrow would be the most you should be at with a cold system. Makes no sense to have such a small area for heat expansion
 

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I checked my LMM which has the same type of system and the correct level is no where near the top. This is a closed system with the reservoir allowing for expansion and contraction with the heat of the system. Even at full operating temp it should be no where near the cap or overflow. Show me the marks on the side of the tank if what you say is correct. View attachment 1092247
Did you not see the arrows in the picture? The expansion reservoir is underneath. A completely different reservoir set up than your LMM. That level is perfectly normal. Ive worked on more L5Ps than you can count on 4 hands.
 

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The coolant drips below off the crossmember below the oil pan
That makes sense and the tiny little coolant lines for the DEF injector run along side of upper oil pan back to just below the down pipe. That would be my first guess. Then if not that the coolant lines for bottom EGR valve which above pass side manifold would be next thing to check.
 

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The coolant reservoir has 2 chambers. The overflow tank is behind and underneath the reservoir. I had the same issue that you're having and I removed my reservoir and found a crack in the expansion tank on the back side near the firewall. The only time it would leak is when it was hot and there was coolant in the expansion tank.
 

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The coolant reservoir has 2 chambers. The overflow tank is behind and underneath the reservoir. I had the same issue that you're having and I removed my reservoir and found a crack in the expansion tank on the back side near the firewall. The only time it would leak is when it was hot and there was coolant in the expansion tank.
Interesting. I guess that would be something else to check except did it drip off under the engine like he said?
 

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It was dripping and mixing in with the A/C evaporator drain water.
 
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