I am realy starting to wonder about this block..... I have done everything possible to get it cooled off.... The intake gaskets are correct and I moved the sending unit to the intake re adjusted the timing and carberator.... nothing is changing anything..... I have run across alot of posts from others with this crate engine claiming the same problems and they are all saying that the block is restricting flow do to poor cleaning of the block and that there is still crap in the block when they assemble them that just gets baked into place and restricts the flow.... I dont know if this is the case but if it is gm is realy not looking to improve the market of sales.... I find it hard to believe that GM would sale such a sloppy peice of work as I have never had a problem with any chevy engine untill now.... It sure seams that this engine is getting alot of negitive feed back from many that have run into troubles with it......

First time I believe you mentioned this is a crate motor. Which crate is it?

Nah. Post #1: "I have purchased a new gm performance 250hp 350 and am now having some problems with the install...."

The cause of the heating issues isn't because of anything like sand being baked in the block- the engine has the casting sand removed, the block gets cleaned and machined. No baking is involved after the initial casting.

That doesn't mean there can't be casting sand left in the block, but for there to be so much that the cooling was affected negatively... I say no way.

If you want to see what's in there, it will mean pulling the pipe plugs from the lower sides of the block and rooting around w/a stiff piece of wire. Pulling the heads is another way to probe around and see what you can knock loose, sand-wise.

It's something much more related to the engine parts and tune than sand left in the engine, IMO.

10067353 GMPP long block.... It was purchased from summitracing... It was supposed to be a 250hp engine but now they have changed the add to 200hp wich is kind of disturbing to me.... I would have ordered the 290hp block had I known that it was being false advertized.....

On another note... Something finaly happend tonight that I am having troubles explaining.... I fired it up tonight when the hot weather cooled off and was running it about 2000rpm and suddenly I was sprayed with a mist of coolant.... This is the first sign of any leaks I have had.... The waterpump was trickling down to the lower hose and I shut it off and it made a nice little puddle of Rust colored coolant right underneith the jeep on the ground.... Nice brown rust color.... I cant explain this becuase all the coolant else where looks nice and clean....... What has happend here? when I shut it off the leak stopped.... Blockage somewhere???? Any thoughts would be great as I think this could be the clue we have been looking for... This is the second pump that I have installed and the first was pumping just fine as far as I could tell.... So i will put the old pump back on....

Sounds like a bad water pump to me. R&R it and retest.

what i am wondering is if I have some blockage somewhere that has made the waterpump fail..... And why is it that when it did it puked rust brown coolant when all the rest of the coolant is looking clean.... where did the rust come from....

I would flush the system at this time.

Inside the water pump there's an air space between the outer bearing/seal and the inner seal. In between the two, water can collect. And rust the internals of the shaft and housing.

You won't see this rusty water until the seal fails. Usually the water will come from the vent at the bottom most part of the WP snout.

A blockage won't cause the pump to fail, IMO. It's designed to stand higher pressures than the cap does. It relies on coolant as the lubricant, so as long as it's wet, it's happy.

Okay well I am out for the night..... I will pick up a new water pump tomorrow after work and install it and see what happens.... Since I am replacing the pump I will get some new coolant and flush the system and make sure everything is good..... Just one more question for you guys.... On this new engine I know that the oil is tuchy as to what you want to run for break in... but what about adding some of that flashy royal purple to the coolant.... would this be a good idea or bad idea? Any thoughts?

Well thanks for taking your time yet again for me today guys.... I hope that there will be some satisfaction in the end of this mess....

My opinion is to save your money. 1/3 coolant to 2/3 water is a good summer mixture ("coolant" is antifreeze, for this discussion).

50/50 is most often recommended and is fine, if a bit overkill. 70/30 is the max coolant to water that is recommended, IIRC.

They (Summit)could also be putting on the "305" engine heads. Cheaper stuff and teenie tiny valves and combustion chamber.

It is another easy check to do on the head casting numbers. It happened on my friends' 350 boat motor(not Summit).

I would wanna open up that water pump and find out what happened.

Once again best of luck. If any more ideas come up I'll be back to pester ya.

That is a great motor with a terrific history.

The OP has said this is a GMPP long block. It was bought from Summit, not built by Summit.

Thanks for that link 454c10 I think I will try and change some things with my timing as I am using a ported/timed vacume..... I did get a new water pump on it tonight and it yeilded no resualts..... I have my current timing set @ 14 degrees initial, 32 degrees mechanical, and ported vacume.... I think I will start by switching to manifold vacume first and re adjust the idle and see where the initial is with the vacume hooked up.... From what I understand it should be about 25 degrees.... I have an adjustable vacume canister on my distributer..... So I think I could dial in about 10 degrees of vacume advance at idle and this would still put my total mechanical timing @ 32 degrees at 2800 rpm...

when I spoke with summit they told me that gm wanted this engine to be run @ 10 degrees initial timing, 32 total mechanical @2800rpm and then to hook up the vacume advance and it would be good to go....

The problem I am having is this.... when I set my initial @ 10 then I can only get 28 degrees of total mechanical....

I have a msd streetfire distributer and it has an adjustable vacume canister on it.... What I need to know is where you guys think I should be running the initial and total mechanical without the vacume.... I can push it up to 18 degrees of initial and that would give me 36 degrees of mechanical.... then hook up the vacume advance and shoot for another 7 degrees of advance at an idle.... would this make it run cooler? this engine has no smog on it what so ever.... just air fuel and spark....