coolant leak


Asked by Sep 14, 2016 at 06:47 PM about the 2003 Pontiac Grand Prix GT

Question type: Maintenance & Repair

I have a small amount of coolant on the ground between the back of the engine and the firewall.  Pressure tested, no loss of pressure with the tester on all day.  Not intake manifold, just replaced the gaskets.  Not the elbows.  Not a freeze plug.  It leaks when the car is cold.  If it is warm or running, it doesn't leak.  The drip is coming between the oil pan and the transmission fluid pan.  I've checked hoses.  Car does not over heat, just noticed small amount on drive.  Maybe a few tablespoons.  

9 Answers


Sorry, forgot to provide info. 2003 Pontiac grand prix, 3.8L, not super charged

1 out of 1 people think this is helpful.

I would isolate the heater core and test that individually. See if the puddle is near the drain tube from the heater core box. You may have a tiny leak in the heater core that is dripping out the drain tube to the ground. When the engine is running and everything heats up the leak seals.

2 out of 2 people think this is helpful.

Check your belt tensioner. There's two plastic elbows that carry coolant from the engine, through the tensioner, to the heater core. They can be sneaky leakers. If that is the problem replace them with the better metal elbows. The two heater hose connectors on the belt tensioner are also suspect. Check them as well. HTH. -Jim


The knock sensors screw directly into the cooling system. Check them. HTH. -Jim


Did you do the lower intake? Or just the upper? Did you replace the plastic upper intake and not reuse the original one? They crack. HTH. - Jim


It's not the elbows, replace intake upper and lower gaskets. Gaskets are metal. Coolant collects on a bolt between the tranny and oil pan. Where are knock sensors located?

1 out of 1 people think this is helpful.

Knock sensors screw into the bottom of each head. One per head. You'll have to jack up the front of the car to see them from underneath. HTH. -Jim


Seems like the only way to see the leak is to drop the tranny. What are options? Freeze plug? Rear seal? Anything else?

1 out of 1 people think this is helpful.

There is a dye you can add to the coolant to trace leaks using an ultraviolet light. Freeze plug is a good suspect. These engines rarely, if ever, have head gasket issues. So I'd rule that out unless there's definite evidence of it. The block and heads are cast iron like in the old days so that's a big plus! The intake gaskets fail because you have plastic, aluminum, and cast iron all bolted together. Each has a different expansion and contraction rate when heated then cooled. Personally I wouldn't drop the transmission unless it's absolutely necessary to get to the freeze plugs. I've never replaced the freeze plugs so I really don't know (yet) what's involved there. Try the dye and see what you can find out from that. HTH. -Jim

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