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Old 12-03-2002, 06:55 PM
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Post Chevy 250 woes

I have a 250 cid in my 78 Nova with a brand new Rochester Single Venturi Carburator. It has 100,000 miles now and I have a few major problems. Last summer my thermostat stuck closed going down the freeway in 90+ degree heat, causing the coolent temp to go beyond 250 degrees. Ever since then, it has burned oil bad enough to foul the plugs every six thousand miles or so. I figure that is due to either the rings being toasted or the cylinder walls being scraped. But before that, and it continues to do so, the lifters tap so hard when the engine is cold, that you'd swear the rods were knocking. I think might be an oiling problem but when starting the car for the first time after changing the oil, the normal loud tick goes away after a few seconds. The car sat for over ten years before I started driving it.

What I would like to know, if anyone can help me, is whether the lifter problem can be solved without a major rebuild. I'm afraid that a lifter is going to stick soon and snap my camshaft into itty bitty pieces. I have also been getting 10-13mpg since the overheating insident, and would love to better that.

One other thing that is getting to me is how the engine temp changes. When I warm my car up in the morning or drive around town at 35mph or slower, the temp never goes beyond 180(the rating of my new racing thermostat). However, whenever I run on the freeway at 65-70, the temp will shoot up to 190+ and stay there until I get off the freeway where it will drop to 180 again (this is in 25 degrees F weather). This is exactly backwards from normal, right? It used to overheat, so I did put a factory v8 radiator for that year in it instead of the little 6 one. I used to overheat in the summer after the insident, but I still run too warm for comfort in the summer with the new thermostat and radiator.

Sorry about the legnth. I really don't want to rebuild it now, and I am trying to get a small block for it and really need this engine to last until them, being that this is the only car I have. Any input on my situation will be apreciated. Thanks

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Old 12-03-2002, 07:10 PM's Avatar
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you probably did in the rings as you suspected, probably also cooked the rocker arms and balls also, part of your cold start noise may also be piston pins they take a lot of abuse and on an overheat they will gall material from the piston pin bores and really clatter when cold. 2.5 gm motors all suffer from this problem after a hundred thou or so. get to work on that new small block cause there ain't no miracle cure for the six,she's tired .
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Old 12-03-2002, 07:18 PM

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I agree with bacroman on that one, did u do a compression test?? If the rings are bad and u have bad compression that can make for bad gas milege. If it is the lifters you think, on those 6 cylinders its so easy to change the lifters. Not even an hour job, just need new lifters. For the time being to mask the problem, you may wanna try some of the supper thikining oil aditive, it may help
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