Rebuild question

[BamaJohn]

I’ve been loosing coolant recently, about a quart every other day. ad I had replaced the coolant a few weeks ago, flushed the system and replaced the thermostat. I’ve checked for obvious leaks around housings and hoses without finding the problem. Next I’ll do a compression test and wait for the bad news. What I’m seeking is advice or opinions on whether to rebuild or replace the engine should it need it. 1991 L98. Auto, 91,000 miles. Would it be wiser to put a crate engine or rebuild the stock motor? I’ve rebuilt the suspension and replaced most every component in the brake system. For a 91 it looks and rides pretty good. Thanks in advance. BamaJohn

 

[vette1985]

My suggestion is to find where it is leaking first. To do a rebuild when not needed, unless you intend on building it for horsepower, would be a waste of money. If you find after that a rebuild is needed, use your existing block. I did and found that I got 334HP with mild bolt-ons, but the components inside are better quality than you will get from some crate motors. Also you will be able to mix and match the components to your liking. Most replacement motors you get what they offer or pay additional to upgrade. If you are going to pay, get what you want the first time around.

 

[tntcorvette]

I’ve been loosing coolant recently, about a quart every other day. ad I had replaced the coolant a few weeks ago, flushed the system and replaced the thermostat. I’ve checked for obvious leaks around housings and hoses without finding the problem. Next I’ll do a compression test and wait for the bad news. What I’m seeking is advice or opinions on whether to rebuild or replace the engine should it need it. 1991 L98. Auto, 91,000 miles. Would it be wiser to put a crate engine or rebuild the stock motor? I’ve rebuilt the suspension and replaced most every component in the brake system. For a 91 it looks and rides pretty good. Thanks in advance. BamaJohn

Find out where the leak is first. Have you pulled the spark plugs and checked them? How does the oil look? It is a creamy brown?

 

[c4cruiser]

Have a radiator shop do a pressure test on the cooling system. Unless you have a hole somewhere that drips coolant out when the engine is cold, it may be some sort of a leak that happens only under pressure.

The cooling system will have around 15psi at opeating temps. This is enough to push coolant out of a tiny hole that would otherwise not leak when coolant temps are cold and no pressure in the system.

A quart of coolant is a pretty fair amount to lose, so you might try checking all of the hose clamps for tightness. No need to really "reef" on the clamps but they should be snug. Do you see any puddles under the car after it sits overnight. If so, where they are located under the car may give you an idea where to look. Another possibility is a leaky freeze plug. Depending on how well the cooling system was maintained, it's possible that a plug can corrode to the point of leaking. Have a shop check their condition. They can be replaced on the car if one is bad.

Unless you find out you have some problem like a cracked block/head, is there any reason you want to consider a rebuild (outside of more HP )? 91K on the motor is not really that bad unless there is signs of wear. A compression check will tell you that. Is there any oil smoke? A little puff at start-up can be expected and that may just be valve stem seals leaking.

Your motor can be rebuilt by a competent shop, but you should be sure of the quality of the machine work to be done. Some shops only do a quick cleanup of block dimensions, some will simply replace your crank with a reground and add oversize bearings, new rings on your pistons with a cylinder hone, a generic "RV" cam and a quick valve job. You should plan out a very specific list of things you want to do, insist on high-quality parts, and make sure the shop puts everything in writing. Once you start to specify all-new parts, rings, bearings, pistons, specific cam, and machine work, the costs of a rebuild goes up quickly.

A crate motor like the ZZ4 for example, is put together with all new parts that are matched together and comes with a GM warranty. There are also a lot of aftermarket engine builders that have complete packages. Check out Summit Racing www.summitracing.com for some of their engine packages from GM and aftermarket sources.

 

[WradDad]

Did you replace the radiator cap when you changed out the coolant? I've had a bad cap give me the exact same problem.

Barry

 

[Edmond]

John,

Like everyone else said, I would first find the source of that coolant leak before tearing that motor apart. Of course, if you're searching for more HP, then go for it!

Is your radiator the original radiator? If it is, check that and the hoses and clamps on there. If it is the original radiator, it's 13 years old and having a leak isn't uncommon. Also, check the drain plug.

 

[WhalePirot]

If you do find some rust on the spark plugs, don't delay too long in the repair. The coolant in the cylinder steam-cleans the oil from the walls, greatly accelerating wear.

Chocolate-shake-appearing oil means quick attention as well, from the oil mixing with the coolant. Subsequent compression testing MAY help point to a head or block crack, but you are not quite to that stage yet.

 

[BamaJohn]

Thanks for the replies, and good advice. I wasn’t contemplating an engine teardown until I did a compression test. I was just thinking out loud trying to decide to rebuild or replace. All the info here sure helps. I believe the radiator cap maybe the problem. I don’t know if this is the original unit or a replacement. It’s a 13 lbs cap is this the correct pressure for this year model? Thanks jb

 

[WradDad]

BamaJohn,

I believe that it should be 16 pounds. Go down to Pep Boys and check their book. Shouldn't be more than 5 or 6 bucks.

Barry