2000 S10 Blazer 4.3 engine.
This is my son's vehicle. A little background first. He called a while back and said he did not have any heat. We replaced the thermostat and flushed the heater core. Got his heat back.
A couple weeks later he called and said he is leaking coolant out of the back of the engine. I told him to check the lines going to the heater core as I reused the original hose clamps and figured that was the problem. Was not. I went to look at it. The coolant is leaking out of the back of the engine and dripping off the bell housing. He says the engine never got hot. He was leaving work and a guy stopped him and told him that when he left he saw black smoke coming out of his exhaust. He drove to a freinds house and asked him if he saw the smoke the friend told him to shut it down. He was leaking coolant. He let it cool down then put some water in the radiator and drove the rest of the way home.
Not sure if any of this has anything to do with it but thought it might help. Anyway the coolant leaks out very fast whether the engine is running or not. I can not see where it is leaking as there is not enough room to see anything between the engine and the firewall.
I get conflicting answers whether there is a freeze plug in the rear of the engine. A forktruck mechanic who I trust alot says no. There are two plugs in the rear but one is for the crank and one is for the cam. Neither has anything to do with the coolant. I also hear that the intake manifold gaskets go bad on these engines. Would water pour out if it was bad? Also saw some posts on the temperature sending unit. Where is this located at?
Sorry for the long post just do not want to pull this thing apart without really knowing anything to look for.
Oh all hoses look good and freeze plugs on the side of the block are dry.

 

When I was younger I made a big mistake of mixing two different types of coolant in my grand am. everything got clogged and It overflowed everywhere. It cost me over 1000 to replace everything. But, that was my own stupidity. It is essential that you check to see where it is leaking from. It could be leaking from the overflow, which would tell you there is a problem with the circulation. Or, your water pump could be finished and leaking from there. As for the freeze plug, I would really doubt that would be the problem as for it might be one of the most rare things that could happen. Manifold gaskets are a common thing on gm's, but again you would have to see it leaking fromt there before. Dry the engine and get your mechanic or self to test the coolant system by putting pressure on it with a pump, no more than 7 lbs, from there you should see where the engine is leaking. To be quite honest though, with the smoke and all, my best bet would be the head gasket. Removing the plugs might show you coolant in the cylinder but the smoke would be white, not black.

 

There are only freeze plugs on the sides of the '96+ blocks, two per side. None on the back.

As far as where it is leaking from, most likely spot is the lower intake manifold gasket. Rarely do they all out fail to the outside, but it is possible. Check your oil. If it looks normal, then drive carefully to get it where ever you need to get it to do the repairs. If it is milky, call a tow truck and hope you didn't already smoke the bearings.

The coolant temp sensor is located on the driver cylinder head about 2/3rds of the way from the front above the exhaust manifold.

To check the head gasket integrity, run a compression test on all cylinders. They all should be within 10% of each other.

 

Thanks for the replies. Oil looks good.Will run a compression test on the cylinders maybe tomarrow sometime. I am going to trailer it to my garage tomarrow morning. Water pump is dry as is the front of the engine. I really do not think you could do a pressure check on the coolant system as fast as the coolant runs out.

 

two weeks ago I replaced the lower intake manifold gasket in my '00 Blazer. I had trouble keeping coolant in the truck. When I was ready to pop the intkae off, it lifted right off. It wasn;t stuck in place like it should have been. The gaskets where attached on the sides, and hung from the intake all rubbery and slimmy. I haven't had a problem in two weeks. The kit is $30 from Autozone, plus new coolant and distilled water, and I bought a full utbe ot Black RTV. The kit comes with RTV, however I dont trust the kit has enough for my messsy ways.

While I had the intake off I cleaned all the carbon out of it. That took some time, air, brake cleaner,Dawn dishwashing detergent,wire tooth brush, and wire battery post brush. My engine fells new again. Its got power, get up and go, and runs great. My idle is back to normal, and it coasts forever now.

 

There is a new gasket kit that has an aluminum frame over-molded with rubber for the sealing surfaces. This approach is what GM has gone to on the 'problem' motors as far as LIM gasket failures goes (3.4L, 3.8L, 4.3L, 5.7L, etc). They cost a bit more, but I would definitely recommend them. They are much improved over the old plastic frame gaskets.

 

Is this a dealer only part or can I get it at any parts store?

 

Felpro makes it as well. CLICK HERE for more information.

 

Thanks! still need to figure where the coolant is coming from but if it is coming from the lower intake manifold I will know what to get.
I know you guys are just being kind as not suggeting a cracked block or head and I know that is a possibility but this is the same engine that our forktruck at work has. The truck at work has been abused and runned hotter than I am sure this one has. Cross your fingers and I will get back to you.
If anyone has any other suggestions post up!

 

If it was a cracked block or head you would have otehr sysmtoms, namely white smoke out the tail pipe (huge white cloud), milky white oil, or pepto bismal looking tranny fluid. You haven't mentioned any of those yet so I doubt your head or block is cracked.