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Old December 2nd, 2006, 11:24 PM   #1
Fryguy302
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Default 96 Vortec motor questions, experts please help.

Summary of my questions:

1. What can cause HC to show up in the coolant other than a head gasket?

2. Can a head gasket be blown or a head cracked even when the truck runs great, has great power, doesn't use coolant, and passes cylinder pressure and coolant pressure tests?

I'd much appreciate it if any experts can answer the above two questions for me. If you want to read the long version, here it is:

Trying to figure out my newly purchased 96 Yukon. I know the previous owners of this truck and know the history on it. For the past year, it's been having a problem starting when cold. It is NOT the typical fuel pump or regulator or ACT sensor issue, because the problem is the way in which the truck CRANKS when cold. When it's cold, it cranks fast for maybe one revolution, then cranks really slow (too slow to start sometimes), almost like something is binding up or the starter is failing. The starter has been changed twice since this problem presented itself about one year ago. The battery has also been changed. The previous owners continued to drive the truck every day like this.

When I bought the truck, I dropped it off at a local shop for diagnosis, expecting them to find a bad ground or a bad positive cable, or maybe a bad starter.

They shocked me by telling me that the head gaskets were probably blown or a head was cracked. They told me they put a wand to the coolant and there were hydrocarbons in it. They also told me they did a propane test and there was an intake leak. When I asked how that affected the starting, the tech told me that he thought maybe it was actually hydrolocking because of coolant in a cylinder. He told me I should probably just put a new motor in the truck, since it has 100k on it anyhow.

At this point, let me tell you how great this thing runs. The oil has been changed every 3k miles for the last 65k (that's how long the previous owners had it). It idles quietly, runs and drives great and is very strong. When I picked it up from the shop, I had my buddy drive it home, and I followed him, so that I could look for smoke. He stood on it one time, and not only was there no smoke, but my brand new 5.4L F150 could not even keep up with the old Yukon, he just walked away from me, even though I had my new truck floored.

We got it home and did the following:

1. Pulled a valve cover just to look. No milkshake and not even any sludge. Looked like new. Oil on stick looked great also.

2. Pulled plugs. No sign of any cyl. burning coolant.

3. Did a cylinder pressure test. Lowest hole = 190, highest hole = 195. I've put seen brand new motors which were less consistent than this.

4. Did a cooling system pressure test. Dropped 2psi in 9 minutes.

The previous owners were shocked, and swear that this truck has never overheated or used coolant. I drag race as a hobby, and run a Mustang that's had many different superchargers on it and is now turbo charged. I've blown a LOT of head gaskets in my day, and I've never seen one like this with no symptoms.

Please let me know what you guys think. Any help would be greatly appreciated.
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Old December 3rd, 2006, 12:32 PM   #2
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They told you to "just put an engine in" because they didnt want to admit they couldnt find the problem. If somebody told me my chevy needed a new 5.7 cos it had 100k miles Id kick them in the nuts.

If Im not mistaken hydrocarbons are going to find their way into the coolant no matter how tight the engine is... especially over 100k miles. Its probably never been changed (dex-cool)

I would still be looking for high resistance between the battery and the starter.
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Old December 4th, 2006, 12:10 PM   #3
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I would change the intake gaskets at least.. They are famous for them leaking..
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Old December 4th, 2006, 12:18 PM   #4
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If hydrolock IS the cause then I would think you should be able to see the coolant in the cylinder.

Disable the ignition and the fuel injectors and crank the engine. If it starts with the slow cranking thing, pull the plugs and see if theres one with water on it...
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Old December 4th, 2006, 04:51 PM   #5
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If there was enough coolant to lock up the motor there would be coolant missing from the cooling system and ALOT of white smoke, if not a broken engine.

I agree on the electrical resistance part, this is the most likely issue. Wondering also if the starter cylinoid could be bad; if it was not replaced with the starter it might be worth a shot. I'm guessing its a wire or battery issue though.

Some other long shots to check while i'm thinking about it; ac clutch and cooling fan clutch, make sure all your pulleys are free and your belt isn't too tight. That can add significant amounts of drag to the engine which would cause the symptoms you describe.
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Old December 5th, 2006, 02:12 AM   #6
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Quote:
Originally Posted by shredder70 View Post
I would change the intake gaskets at least.. They are famous for them leaking..
x2. My '98 Silverado needs intake gaskets, as did my '97. Bigtime issue with the stock GM intake gaskets. I loose coolant at about 1gal/3k miles, trips off the O2 sensor code.
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Old December 5th, 2006, 07:37 AM   #7
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Check to make sure that your engine block is grounded directly to the battery.
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Old December 10th, 2006, 12:57 PM   #8
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Quote:
Originally Posted by CHVYPWR View Post
x2. My '98 Silverado needs intake gaskets, as did my '97. Bigtime issue with the stock GM intake gaskets. I loose coolant at about 1gal/3k miles, trips off the O2 sensor code.
I had this same problem with intake. but,.....showed loss of dex-cool.
the engine started and ran fine.
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Old December 10th, 2006, 10:06 PM   #9
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I'm going to get the intake gaskets done regardless, but I think the engine is fine. We ran it the other day for almost an hour with an air tight funnel in the radiator cap opening. There was not a single bubble, and the thing never got over 186 degrees.

Also, I was thinking how when it has the cranking problem, it sounds like my race car sounds turning over, when I have too much initial advance in it.

To test that theory, we let it sit all day and night again, then disabled the fuel and spark and tried to turn it over. It turned over strong and fast. There is no hydro leak issue with this motor. I can't figure out what could cause it to act like it has too much advance in it though.....I know the computer controls the spark on it. Any idea where I could take this thing where they really know what they're doing?

Thanks for the info guys.
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Old December 10th, 2006, 10:21 PM   #10
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Quote:
Originally Posted by Fryguy302 View Post
I'm going to get the intake gaskets done regardless, but I think the engine is fine. We ran it the other day for almost an hour with an air tight funnel in the radiator cap opening. There was not a single bubble, and the thing never got over 186 degrees.

Also, I was thinking how when it has the cranking problem, it sounds like my race car sounds turning over, when I have too much initial advance in it.

To test that theory, we let it sit all day and night again, then disabled the fuel and spark and tried to turn it over. It turned over strong and fast. There is no hydro leak issue with this motor. I can't figure out what could cause it to act like it has too much advance in it though.....I know the computer controls the spark on it. Any idea where I could take this thing where they really know what they're doing?

Thanks for the info guys.
If you are near the Bay City area you can bring it to my shop. I am a certified Master Tech and I have the latest and greatest diagnostic stuff that keeps me in the poor house with Snap-On. I offer a 10% discount on parts and labor to members of this forum and if I can't find your problem I don't charge for my time.

You mentioned somebody testing for HC in your cooling system, not really familiar with that testing. My system checks for CO and CO2 and is very sesitive to small leaks. I'm suprised the shop that was replacing all the starters didn't do a current draw test before condeming the starters. All things considered, something is just not adding up with your starter issues. If you find somebody near you that fixes the problem PM me with the results, I wouldn't mind knowing what the problem was for future reference.
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Old December 17th, 2006, 10:38 AM   #11
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Update: Replaced the starter and battery again, been driving the truck every day, and have had no problems. It runs great.
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Old December 23rd, 2006, 01:47 PM   #12
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Hopefully you have it fixed, I have seen the flat style dist. cap crossfire internally and cause some weird problems, not sure if yours has that one or not.

FYI: We test for headgaskets at my shop with a 5 gas analyzer all the time.

I have found it to be one of the best ways to test for headgasket problems.
Most good engines have less than 50 PPM in the cooling system, anything above 100 PPM and something is leaking. If you had one leaking so bad it was hydro-locking the engine, you would have 1000+ PPM in the cooling system, plus white smoke, coolant in the oil and a eng. miss for a minute or two after the engine did start.

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Old February 1st, 2010, 08:15 AM   #13
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I just wanted to update this ancient post in case anyone found it from google and had a similar issue. This problem actually turned out to be an intermittently bad crank sensor. It would cause the initial ignition timing to spike very high when cranking (intermittently). Replacing the sensor fixed everything.
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Old February 1st, 2010, 10:17 AM   #14
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lol i should read dates
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Old March 4th, 2010, 10:04 AM   #15
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Quote:
Originally Posted by CHVYPWR View Post
x2. My '98 Silverado needs intake gaskets, as did my '97. Bigtime issue with the stock GM intake gaskets. I loose coolant at about 1gal/3k miles, trips off the O2 sensor code.
x3 Gm using silicone on OAT coolant was just dump.... Get some of the new gaskets from Victor Reinz that are made of HNBR.
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