Edmunds Answers

Answers

  • zaken1 09/02/10 3:31 am PST

    The compression test results are right on the edge of failing: There is a 15% maximum allowable difference between any two readings; and the 150/175 difference actually fails that standard if you take 15% of 150 (which is 22.5). A visual check for cracks or warpage is not adequate; the head must be tested by a machine shop that has crack testing equipment (magnaflux or zy-glo) and a level plate and dial indicator, or a surface grinder to take a light cut on the head to display any warpage. If the machine shop finds no cracks or warpage; the valves should probably be reground.

    It is unfortunate that you went to all the work of pulling the heads; without first pressure checking the cooling system. Bubbles in the coolant are not always an indicator of bad head gaskets. One other cause of bubbles would be if this car has GM DexCool antifreeze in it, there is a known problem with that particular antifreeze formula attacking the silicone intake manifold gaskets which were used on many GM vehicles; and allowing air to leak into the cooling system. There was a huge class action lawsuit against GM because of that; which they got out of when they declared bankruptcy. I don't know whether this motor used silicone intake gaskets; but you should be able to find that out.

    There is also an electric radiator fan on this vehicle; which is designed to run when the coolant temperature exceeds a preset value. This fan is activated by a radiator fan relay; which is known to be unreliable. If the fan has not been running; it will make the engine overheat. In that event, I would replace the radiator fan relay.

  • hpinch 01/25/11 5:09 pm PST

    I have a similar problem with 2000 OLDS INTRIGUE. I just had the water pump, thermostat and radiator replaced, but it did not solve the overheating problem. It overheats only when driven slowly (around 40MPH) with small throttle openings or low engine speed below 1500 RPM. No problem on the highway or at engine speed above 2000 RPM. My mechanic is now recommending a head gasket replacement. He suspects that part of the gasket is blocking the coolant opening. Did you check that on your gasket?

  • afab1948 07/08/11 5:05 pm PST

    Air is trapped in your engine. It can only flow past your thermostat above 180 degrees. The air gets trapped in the lower right hand side of your motor so the thermostat doesn't open. The thermostat is also spring loaded. Above 2000 rpms. it will open so the car runs ok at highway speeds. I have fixed two of these it's cheap and pretty straight forward. Pull your thermostat and drill two 3/16 in. holes in the engine side of the of the silver disc ( round sheet metal that hold the antfreeze into the block. I set my holes 180 degrees apart with one up and the other down. You can buy a new gasket for a couple of bucks just to make sure you get a good seal and a little thread sealer on the bolts is always good. Refill your engine and use the little plastic bleeder screw to get most of the air out. This screw only has to come out partway to get fluid out. If you get tired of fighting with this little plastic tab you can cut a notch in a 1/4 in. drive small socket. leave the top off your over flow tank for about 10 min.. The rest of the air should get out on it's because it can now get by your thermostat. Good Luck

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