Buick Century Coolant Leak

I’ve got a ‘98 Buick Century with 142,000 miles. This is the 3100 v6 engine.

I’ve had minor coolant leaks for the last couple years, managed with topping off now and then. Recently replaced the radiator, only to then discover a more serious coolant leak coming from the timing chain cover gasket. The oil has looked normal last several oil changes, so I don’t think I have coolant leaking into the oil.

Question now is, does anyone know about how much it would cost to have the timing chain gasket replaced? Working on getting a quote from my mechanic, but they initially hinted at doing a full timing chain job if they were going to be replacing the gasket anyways.

I’ve done a number of repairs on the car myself, but have to admit this one seems like it might be beyond what I have the capacity to DIY.

As of now I am topping off the coolant somewhat regularly, and the leak is a pretty consistent drip.

Coolant is not too expensive but I’d like to stop worrying about the engine overheating, doing any further damage.

It’s an older car but really like the way it drives and it’s been so cheap to maintain.

This sounds like it could be a bigger job $$$, would folks recommend going ahead with the repair so long as the rest of the car is in decent shape? Any thoughts are appreciated!

If coolant is leaking from behind the timing chain cover, then it could be coming from a leaking frost plug.

You can see a frost plug thru the bottom of the cam sprocket in this image.



Yes. Even if the proper repair costs $2k, which I doubt it will cost that much, the question becomes “what would the alternative cost?” and the answer is “a lot more”. As long as the rest of this car is in decent condition–meaning that the engine runs well, the transmission shifts smoothly, the body and interior are decent, you should fix it properly. Don’t cheap out and run this car into the ground. It’s difficult to find a good, dependable used car these days.

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Unless I am missing something, there is basically no way for coolant to be leaking from behind the timing cover without mixing with the oil… The freeze plug (frost/core plug) that Tester showed would be dumping coolant into the oil a longtime before it leaked past the timing cover…

You probably have a cracked timing cover in a coolant passage or some other problem… So if your mechanic says it is leaking from the timing cover gasket, the labor would be about the same, but you will have the added expense of the timing cover itself… A timing cover maybe hard to find without going to a junk yard…

I would probably get a 2nd opinion… Or get a pressure tester and a good mechanics mirror and start looking really hard…

I am guessing you have a lower intake manifold leaking making it look like the timing cover gasket it leaking, much more common repair…


Yeah my memory is a little foggy but there should be only oil behind that cover. Maybe it is the water pump and you are being deceived.

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That’s what I did with a borrowed pressure test kit from O’Reilly’s. After overnight under pressure, I could see the source of the leak. And it was an intake manifold leak. Bought the gasket when I returned the test kit and fixed it that day. Had a Haynes manual. A time consuming job that took some thinking and improvising, but doable, done, and satisfying.

Good luck!


A co-worker’s Monte Carlo’s timing chain cover was leaking coolant from a failed gasket:

I’ve had good luck using “Bar’s Leaks”. But only for small leaks. You might have let this go too long. But if the car still runs and drives ok I’d try it. Nothing to lose.

I think that era motor had cast timing cover with WP cartridge. It’s not a stamped steel timing cover.

Timing chain replacement is 7.0 hours of labor.

Timing chain cover w/water pump housing.

And that is what I was missing… lol

No experience with your specific engine OP, but suggest to rule out a leaking water pump first. It can be very difficult to figure out where coolant leaks are actually coming from. About all you know for sure it that leaking water always runs downhill. I suspected my Corolla had a leaking water pump a few years ago, but it was located behind a bunch of stuff in the engine compartment, so the only way I knew for sure the water pump was the leak source was to replace it. Does your 98 Century still have the original water pump?