Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Sludgy Anti-Freeze

11K miles ago, I put in a near-zero mileage 3.1 into my '95 Cutlass Supreme that had been salvaged and sat for 12 years. Also installed new hoses & radiator but left the old heater core. While changing out the thermostat the other day, my mechanic showed me what he had drained out. It was black and sludgy. He recommended getting the coolant system flushed and to put new anti-freeze in. He also recommended not using Dex-Cool, opting instead for the green stuff. Why is my anti-freeze sludgy and is this advice sound? FYI: The car runs great, so I don’t think I have an oil leak. However, he had to switch out the plugs coz one had fouled. It had a dry look to it, not wet; so, again, I’m hoping the problem isn’t oil. On the down side, I am using about a quart @ 1000 miles.

Well, I hate to say it, but a near-zero mileage engine shouldn’t be consuming oil at that rate, and that fouled plug combined with the sludgy antifreze would make me strongly suspect a leaky head gasket. A compression test, maybe even only a partial compression test focusing on the cylinder with the fouled plug, will tell you for sure.

You may have a questionable engine. The near-zero mileage statement could be utter BS and an engine that sat that long could develop problems depending on the environment, where this engine was sitting, etc.

Stuck PCV valve (although this should affect more than one cylinder), sticking piston rings, hardened valve seals, etc. are all possibilities.

Considering the fouled plug and oil consumption the first thing I would do if the car were mine would be to run a compression test. It’s easy to do and will determine if it’s back to the drawing board on a motor; and a possible discussion with whoever sold you the engine.

Forgot to mention that my mechanic checked the compression. 135 in the front cylinders (which includes the one with the fouled plug), 135 in one of the back cylinders, and 125 in the other two. I’m not a mechanic, but am I guessing right that the oil could be getting into the anti-freeze. Why isn’t the anti-freeze getting into the oil?

The guy who sold me the motor said that his son bought some salvage motors and that it had few if any miles on it. I took my mechanic with to look at it, and he said that it looked unused. He turned the fly wheel over a few times and said that it seemed to move smoothly. It only cost me $600, but I have $2000 in after the installation and other new parts. Now I’m wishing I put in a factory rebuilt.

I’m still suspicious of the motor. Was there any explaination for WHY the motor would have few to no miles on it?

But, given the compression test results, I’d assume for now that maybe the engine is okay and get the antifreeze changed (I’m pretty sure this was pre-dexcool, so green stuff is fine) and keep an eye on it and the oil consumption and maybe pull the offending plug every so often.

Quick-n-easy for flushing heater core: Carefully remove the hoses going to and coming from the heater core. Front flush and then back flush with a regular garden hose until nothing but clear water runs. Re-connect hoses. You now have a clean heater core.

He said that his son in Texas bought 100 salvage motors and that this one was basically new. It was stored in a dry garage in NW Minnesota, so I don’t think the seals would have dried out. I’ll sure take your advice–thanks!

I think you been had. The compression readings, even the 135s, mean that motor has some serious issues; probably due to piston rings.

Near-zero, or even low mileage, it is probably not.

You may be right. The car runs great on the open road, but it is a bit noisy. Well, it was worth a try; and, if I get a year out of it, it’s paid for itself.

depends on where the leak is. If it’s in a place where there’s more pressure on the coolant side, then the coolant will flow into the oil. If it’s in a place where there’s more pressure on the oil side, then the oil will flow into the coolant.

A follow-up. I had the system flushed, and now the anti-freeze is holding up–no sludge. I still a quart of oil maybe every 1000 miles, but that’s not bad. This summer, I may have my mechanic check the valve seals. They may have hardened after sitting so long.