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?
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.
2006-12-03 00:20:54 · 5 answers · asked by Iamnotarobot (former believer) 6 in Cars & Transportation ➔ Maintenance & Repairs
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.
2006-12-03 00:21:27 · update #1
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.
2006-12-03 00:21:51 · update #2
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.
2006-12-03 00:22:11 · update #3
If you hydrolock an engine, saying that it's got a problem starting is an understatement. Hydrolocking occurs when a cylinder fills up with water, and if you try to crank over a hydrolocked engine, you're likely to break something. At the very least, you should see a LOT of coolant disappearing, and it would spit a slug of water out the exhaust when it starts. If this thing passes a leakdown test, it almost certainly doesn't have a blown head gasket. I would suspect a problem with the ring gear if it's not the starter - or an incompetant mechanic shimming the starter wrong if the Yukon uses starter shims. (I know some Chevies use these, and if you adjust it wrong, the starter will bind. Not sure if they'd have them on a Yukon or not.)
2006-12-03 04:03:54 · answer #1 · answered by Mad Scientist Matt 5 · 0⤊ 0⤋
This may sound silly, but what did the flex plate teeth look like? Is the flex plate loose or cracked allowing it to move? You have checked off all the right and correct things, I do NOT think it is any of the things the shop told you.. Can you somehow post what you find out or even email me? I want to know.
2006-12-03 00:37:29 · answer #2 · answered by ? 4 · 0⤊ 0⤋
I'm betting on electrical problm to starter, somethings wrong with connection(s) or wire, or even an incorrect starter or one that is mounted wrong (shims?). TEST it by using two fully charged batteries, turn it over, and immediately check for hot wires... carefully.
Would be curious what it turns out to be.
2006-12-03 00:30:45 · answer #3 · answered by ralphers 3 · 0⤊ 0⤋
Not to sure about this one. Check starter connections and flex plate. Good luck with this problem.
2006-12-03 01:49:59 · answer #4 · answered by Anonymous · 0⤊ 0⤋
Whats hc?
2006-12-03 00:26:23 · answer #5 · answered by Anonymous · 0⤊ 0⤋