I appreciate all the replies to my recent spark plug thread, there certainly are some knowledgeable folks here on the forum.So new plugs and wires smoothed out my rough idle for about a week, then it came back. This week I got the Low Coolant warning, and looks like I lost about a quart of coolant. I had been smelling coolant when I got out of the truck, but didn't think much of it since I just changed the heater hoses and recovery tank and it takes a while for the spilled coolant to burn off.I couldn't find any visible leaks nor signs of places where coolant had pooled or looked like it might have leaked. On the burb you have rear climate control, which means heater pipes that run clear back to just ahead of the rear wheel (separate heater core back there), but I didn't see any evidence of leaks or drips on the driveway. No interior fogging or wet carpet, so front core should be OK too.I'm wondering if the intake manifold gasket could be leaking? 171k miles on the truck now. Could a leaky IMG have contributed to the early demise of the spark plugs? Is there a way to tell if the IMG is leaking before taking it off? I recall reading that some 8.1 owners had issues early on with leaking IMGs, but I never had a problem. AFAIK, the 8.1 has never had a design issue with head gaskets, but that doesn't mean they don't fail either.Comments and ideas welcome.

BurbMan wrote:I'm wondering if the intake manifold gasket could be leaking? 171k miles on the truck now. Could a leaky IMG have contributed to the early demise of the spark plugs? Is there a way to tell if the IMG is leaking before taking it off? I hate to ask an obvious question, since I am sure you have already checked this, but do you get white smoke when you first start up the engine?Kind of late to ask, but have you always used GM Dexcool? I've had great luck with Dexcool on my GM vehicles over the years, regardless of what others say. I've known people who developed IMG issues after switching to the green coolant.

Iv'e been looking, but it's hard to tell with the weather lately, I can't tell if I'm getting more steam out the exhaust or not. Yes, I stayed with DexCool, did not switch over to green.

you will smell a sweet smell coming out the exhaust if it is leaking most times its the passenger side back two cylinders

newman fulltimer wrote:you will smell a sweet smell coming out the exhaust if it is leaking most times its the passenger side back two cylindersIntake or head gasket?

I'm not aware of intakes being liquid cooled but never been around 8.1s. Don't think you could loose coolant thru the intake. Leaky img could cause a lean burn condition but if it was leaking significantly then you would not have vacuum. This would be noticable. Sound like an exhaust tick/leak, poor idle characteristics. Could be your problem with plugs and idle. Hook up a vacuum guage and measure vacuum compared to normal range whatever that is.

8.1 Intake Manifold | Good Sam Community

_40Fan
Explorer
Feb 21, 2016
The 8.1 doesn't have a water passage through the intake. They were known for vacuum leaks, but not coolant. I'd be looking else where for the leak.
45Ricochet
Explorer
Feb 18, 2016
Turtle n Peeps wrote:
Use this to find out if your head gaskets are intact.

Or he could just have it smogged in Kalifornia :W
BenK
Explorer
Feb 18, 2016
Similar on my 7.4L big block and turned out to be a tiny crack in the plastic hot
tank of the main radiator. The crack was propagating from the engine
oil fitting towards engine hot line fitting

Baffled me for months till it finally got larger to see the steam...then a tiny, tiny
stream of liquid and of course...just before going to tow a 8K GVWR utility
trailer a few hundred miles to retrieve some wood shop machinery for a buddy

If this is your problem...and running Deathcool...know that OATs does
NOT like O2 in there...so flush it WELL after fixing whatever it is
I'm lucky switched to American Green after almost losing my big block
to DeathCool plugging up the OEM radiator...this one pictured is the
second radiator and that 3rd one is what is still in there

Here is the crack and it was NOT visible till it got this big

mysubradiator myradiator
cdlaine
Explorer
Feb 18, 2016
Burb....

When you get to the resolution phase of this diagnostic event please post your results. Very interested. Good Luck.

Charles
BurbMan
Explorer II
Feb 18, 2016
I know on the GM 3.8 V6 the lower intake gaskets are prone to leaking and letting coolant into the cylinders. A bad enough leak can hydrolock the motor.
Turtle_n_Peeps
Explorer
Feb 18, 2016
Use this to find out if your head gaskets are intact.
LIKE2BUILD
Explorer
Feb 18, 2016
If the 8.1 intake is anything like the intake on the 6.0L in my old '04 2500HD, there is no coolant flow through the intake. On the 6.0 there are small coolant hoses that run through the throttle body but nothing like the old cast iron intakes that had coolant passages all through them.
Grit_dog
Navigator
Feb 17, 2016
I'm not aware of intakes being liquid cooled but never been around 8.1s. Don't think you could loose coolant thru the intake.
Leaky img could cause a lean burn condition but if it was leaking significantly then you would not have vacuum. This would be noticable. Sound like an exhaust tick/leak, poor idle characteristics.
Could be your problem with plugs and idle. Hook up a vacuum guage and measure vacuum compared to normal range whatever that is.
BurbMan
Explorer II
Feb 17, 2016
newman fulltimer wrote:
you will smell a sweet smell coming out the exhaust if it is leaking most times its the passenger side back two cylinders

Intake or head gasket?
newman_fulltime
Explorer II
Feb 17, 2016
you will smell a sweet smell coming out the exhaust if it is leaking most times its the passenger side back two cylinders