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Old 02-22-2012, 11:59 AM
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Calling all experts, rebuild or replace my V8 ?

Hi Guys.
I need some help deciding weather to rebuild or replace my 5.3 vortec engine (LM7) in my 2000 yukon. It has 279,510 km on the engine, never been rebuild before.

Here's the deal. Coolent leak and low/zero oil pressure issues.

A. Coolant leak = head gasket gone!

Evidance:
1. Coolant leak began to to become noticable, up to 1/4 of a quart a day after an hour of driving.
2. Checked all hoses and heater coil = nothing no leaks?
3. Checked radiator no leaks ?
4. Bubbling in coolant reservoir once warmed up to operating temp.
5. Exession moisture from exhaust pipe on start up dripping like a leaky tap.
6. No water found in the oil.
7. No oil in the coolant.

B. Oil Pressure very low or zero on start up = Oil pump gone, valve gone or stuck?

Evidence

1. No metal in oil filter (bearing still ok)
2. No new noise from the engine (bearing seem fine).
3. New oil pressure switch installed recently.
4. Oil pressure gauge works, when rpm's are increased.
5. Oil levels fine, no smoke, no consumption of oil.

So should I rebuild or replace ?

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Old 02-22-2012, 01:06 PM
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I would buy a replacement engine from GM.
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Old 02-22-2012, 01:10 PM
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Water pump replaced 20,000 miles ago.
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Old 02-22-2012, 01:24 PM
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Whats the price difference of the new one from GM and the price of getting the one you have rebuilt?
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Old 02-22-2012, 01:50 PM
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I would check into a junk yard engine. It will probably be half the price and may be less work and down time overall. Tat is a common engine so it should be fairly reasonably priced and the labor to replace is going to be the same no matter which route you go. On a vehicle with that many miles I would try to get out as cheaply as possible.

Have you had to rebuild the rear end yet, it was real common on those.
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Old 02-22-2012, 07:42 PM
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You have to consider that the current motor may have damage that wont show until you tear it down.

I would go the salvage yard route, they always test the motors and give a warrenty.

Unless the truck is in great condition other than the motor, you have to consider the driveline may need other repairs not too far down the road.
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Old 02-22-2012, 10:34 PM
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Thanks for the replay guys.

Firslty, everything except: the rearend (rear diff, axle, seals and bearings), frontend ( front diff), power steering axle, and engine has been recently replaced rebuild.

Secondly I don't want to go the Junk yard option after all that effort.

Thirdly it is a DIY job. Labour is not a factor.

The questions are, is it worth rebuilding the engine with that many miles on it, or do these rebuilt engines have major issues? Has anyone out there got experience with the rebuilt engines?

Thanks again.
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Old 02-22-2012, 10:57 PM
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A properly rebuilt motor shouldn't have any issues, no matter which motor it is. If you have the skills, rebuild it, if not buy one.
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Old 02-23-2012, 08:00 AM
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Do a cost comparison - correctly rebuilding an engine is much more then a valve job, a set of rings and bearings. Very few people have the personally owned equipment to boil the sludge out, mag particle or electronically check for cracks, measure then rebore for new pistons, turn a crankshaft, install new camshaft bearings, true up the head and block surface, install new pistons on straightened connecting rods, install new valve guides and grind the seats just to name a few operations to do a full and true rebuild. You are, to do it correctly, approaching and probably even beyond the price of a NEW factory crate engine long block or one from a reputable rebuilder like Jasper.

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Old 02-23-2012, 08:44 AM
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Thanks Dave

That's clear quality feedback, broken down like that I can see thing$$ a bit clearer, not to mention the time and headache factors and annoying the the wife and kids.

He I will have a spare engine to practice on if need be.

Thanks again
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Old 02-23-2012, 10:40 AM
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for a premiem long block, a local motor co. rebuilder here in town is going to charge me a little less then half the price then If I buy a new GM crate, also to balance the rotating assembly. Ran on a sim machine and and checked. Drop it off , ready in 3 days with my original block and heads just rebuilt with warranty.

Also with this done
equipment to boil the sludge out, mag particle or electronically check for cracks, measure then rebore for new pistons, turn a crankshaft, install new camshaft bearings, true up the head and block surface, install new pistons on straightened connecting rods, install new valve guides and grind the seats just to name a few operations to do a full and true rebuild.

That why I had asked what was the cost involved. It sounds like money is not a great concern with you so go new crate.
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Old 02-23-2012, 05:48 PM
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Not to mention that style engine doesn't bore/hone very well. GM recommends just touching the bores for a good ring seal. Check the camaro and truck forums. They will highlight what is involved with rebuilding that style engine. I haven't touched one in a few years, but I do remember the tolerances(for wear) are tighter than Dicks hatband.

On the other hand, if you do find yourself within tolerances the rebuild is pretty much straight forward and cheap if you reuse the lifters, pistons, rods, and if you have the tools. I guess the point im trying to make is tear it down and take a look for yourself. Im also a big fan of the used engine route.
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Old 02-23-2012, 06:10 PM
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As far as the coolant leak goes, those engine were assembled with plastic intake manifold gaskets that were prone to break and leak. I just replaced a pair in my 4.3L, or I should have said the shop did for about $400. No water in the oil either. If you get one out of a salvage yard beware. Do yourself a favor and Google "intake gasket leak" and see what I'm talking about. Also check some of the truck forums.
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Old 02-23-2012, 06:23 PM
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Quote:
Originally Posted by ssmonty
As far as the coolant leak goes, those engine were assembled with plastic intake manifold gaskets that were prone to break and leak. I just replaced a pair in my 4.3L, or I should have said the shop did for about $400. No water in the oil either. If you get one out of a salvage yard beware. Do yourself a favor and Google "intake gasket leak" and see what I'm talking about. Also check some of the truck forums.
ssmonty
There is no coolant passages in the intake. However, the gaskets are plastic and are prone to vacuum leaks, but not coolant leaks. The 5.3 is based on the LS series engines.

Gasket replacement is a good idea on any used engine. When I do a used engine I always pull the pan and replace the gasket and look at the bearings. Also, pop off the valley pan and look at the lifter valley.
Good Luck

Last edited by ethn_bert; 02-23-2012 at 06:28 PM. Reason: using a darn smart phone and dropping random smiley faces
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Old 02-23-2012, 10:11 PM
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Done the intake already with new bolts and upgraded felpro gaskets, plus the knock sensors etc.

The tolerances are fine as you said ethn_bert, and i don't think I can get this accuracy done locally, including fine crack testing and pressure testing for pin holes in the block.
Around where I am I have some old timer machine shop, that if far form precise in terms or engineering, compared to those high tech robotic CNC machine shops (see attachment).

I would rather have a crate engine with 0 Km than an 80 rebuild engine whose days are numbered.

Thanks again guys for the feedback.
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