Hey guys, have a question about goofy oil pressure and coolant loss.

First, I am losing coolant fairly slowly. Its not really smoking and I can't smell anything from the tail pipe. There also is no leak that I can find.

Second, my oil pressure has started to act funny. It runs low, always below 40 and just above 20 when at hot idle. Before it never got much below 40 at hot idle and would run up to 60 at about 2500 rpm. If I change just the oil there is no change, but if I change both the oil and filter my pressure comes back up to where I would expect it. The pressure will look fine when I drive around town. But, on long trips, 2 to 3 hours on highway, the pressure will drop again and stay below 40 until I change the oil and filter again. Also, the morning after long drives the engine taps pretty hard until warm and then goes completely away.

I would assume that these two are related because I noticed them about the same time but I'm not sure what it could be. Leaking manifold gasket maybe. Anyway, Thanks in advance for any help.

 

Seen cylinder heads crack at the head bolts. Coolant goes into the motor. I find that it sludges up in the oil filter and clogs the filter. That is why engine has noise on start up. There is a bulletin on this condition.



2005 Chevrolet Chevy K Silverado - 4WD | Sierra, Silverado (VIN C/K) Service Manual | Engine | Bulletins By Category | Technical | Document ID: 1986750
#06-06-01-019B: Information on Gradual Coolant Loss Over Time with No Evidence of Leak Found - (Jun 12, 2007)

Subject: Information on Gradual Coolant Loss Over Time With No Evidence of Leak Found

Models: 2004-2006 Buick Rainier
2001-2006 Cadillac Escalade Models
2001-2006 Chevrolet Avalanche, Blazer, Silverado, Suburban, Tahoe, TrailBlazer Models
2001-2006 GMC Envoy, Jimmy, Sierra, Yukon Models
2001-2004 Oldsmobile Bravada
2005-2006 Saab 9-7X
with 4.8L or 5.3L VORTEC® GEN III, GEN IV V8 Engine (VINs V, T, M, B, Z -- RPOs LR4, LM7, LH6, L33, L59)

This bulletin is being revised to include engine RPO L59. Please discard Corporate Bulletin Number 06-06-01-019A (Section 06 - Engine/Propulsion System).

Some vehicles may experience a gradual coolant loss over time. A very low percentage of cylinder head(s) manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.

Inspect the cylinder head assembly to determine if the casting was manufactured by Castech. This can be accomplished by inspecting for their casting logo located on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.

Important: If the cylinder head(s) are Not a Castech casting, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.

Refer to the following illustrations on how to identify Castech casting and/or the very specific areas of the cylinder head(s) for a coolant leak from porosity.


Cylinder head(s) location of the Castech manufacturing casting logo (1).


Close up view of the cylinder head(s) showing the Castech manufacturing casting logo (1).



If the cylinder head(s) is a Castech casting (1), inspect the area around the five oil drain holes for witness marks indicating coolant seepage over time (2).

Important: If No evidence of coolant loss is found on inspection of Castech casting cylinder head(s), follow normal diagnostic procedures in SI to determine the cause of the coolant loss.


The crack location can be found in any of the five cylinder head(s) oil drains. This can be seen as a clean or shiny area, on an otherwise stained surface (1). Pressurizing the cooling system at this time may reveal coolant, air, or a combination, weeping in the described area. If inspection reveals evidence of coolant witness marks (1), replace the entire cylinder head(s) assembly.

 

Yeah sounds like heads need to be fixed, if they can. Do it now to save the rest of your motor.

 

Penn,
You ever get this resolved? Having the same issue with an 06' Sierra. Dad had a similar situation with an 05' after many trips to the dealer and that ticking noise getting worse he ended up replacing the motor. Hoping to avoid that (and the $ that goes along with it). Hope all is well. Thanks.

 

Yeah, I did figure it out. It was a set of the Castech heads that are prone to cracking. There is a service bulletin on it, just search Castech service bulletin. Basically you can identify the heads by a casting mark under the valve cover. If you are have similar problems and you have these heads that's probably it. It seems common enough for a service bulletin but not for a recall or help from GM. If this ends up being your problem make a formal complaint to Chevy, the more people who do they might help someone in the future. Good luck man but definitely get it looked at sooner that later or it could end up being a whole engine.

 

I shoulda reviewed the whole post, it was the problem outline in the SB posted.

 

Just had the dealer confirm that it is leaking. I'm assuming you just did the top half of the motor not the entire thing? If so how has it been? How many miles since the work? You recommend going that route or new motor entirely? It's been this way since early december (when I noticed the coolant being low and engine tapping a little). Thanks for any advice.

 

I just had the heads replaced. I have put 30,000 mi on since the work with no problems. Its a tough call on whether to do the whole engine or not but I have been lucky so far. If I could go back I probably would have had a local performance shop do something like edelbrock heads/cam/headers. I got a quote from a guy and it would have been about the same price as dealership but they already had my truck and I was really hoping GM was gona help with something. Good luck, I know it's a tough situation to be in.

 

Thanks for the info. I'm gonna wait it out. I figure if I'm gonna swap the motor, might as well get all I can out of her before she dies. Heard about Bars stop leak so I'm gonna try that in the meantime so I don't have to buy $18 of dexcool every few weeks. I've definitely given some thought to upgrading while I'm at it. It is a shame that GM wont do anything for us...My family has owned Gm's going back 30+ years. I'll write a letter when the time comes but I'm not holding my breath. Hope yours holds together for you.