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1993 bonneville 3.8, losing coolant. No visable exterior leaks, however radiator has a lot of sludge in it. Oil dipstick shows clean oil. I'm thinking possibly a head gasket problem. Any other thoughts?

Check the transmission fluid. If it is milky, or opaque, you will have coolant in the transmission and transmission fluid in the radiator. This can happen if the transmission cooler coils in the radiator fail. The solution is to replace the radiator, and quickly drain and flush the transmission to get any coolant out of it.

To test the trans cooler coils in the radiator, disconnect the cooler lines and blow out any oil. Then, with water or coolant in the radiator and the cap removed, plug one end of the cooler and pressurize the other end with air. If the coil is cracked, you should see bubbles rising to the surface of the water in the rad.

Remember that water or coolant will fall to the bottom of a crankcase or oil pan of the engine or the transmission. When water or coolant is mixed with oil, it forms an emulsion that will appear milky. But the coolant may not be mixed well, it could be sitting on the bottom of the pan. In the case of the oil pan, this is easy to detect - just drain about a quart of oil into a plastic pan and pour it slowly into an empty container watching carefully for evidence of water or coolant contamination. For the trans, the only sure way is to unbolt and drop the pan.

Bypassing the trans path through the radiator is as simple as disconnecting it and using an external cooler. If you suspect a leak between them, plug the ports you bypassed. Assuming that's your problem, anyway.

Head gaskets? Very unlikely. In over 6 years and thousands of members, we've only seen two that might have been failures, and were never confirmed (other than one crazy fool running twin-boost with a super and turbo).

Thanks. The trans fluid looks fine, nice and pink, no discoloration at all. The engine oil looks O K too. I'll try the trans cooler lines first.Right now I'm in the middle of doing a compression check.

How does your exhaust smell? Any smell of coolant?

I suspect your radiator right off the bat. Small cracks in the sides of it will steam coolant out under pressure, and you'll never see a leak. Otherwise, the leak is going underneath the radiator and its just evaporating on the heated metal objects its landing on. There are numerous ways it can disappear with no signs.

A new radiator isn't a bad idea if you're above 100k and its original...a new one will allow free flow and keep the system clean allowing the cooling fans to work more efficiently. Older ones also, as mentioned can have a corroded transmission oil heat exchanger. If water gets into a transmission, it WILL kill it. It will get into parts of the transmission where it can't be removed unless the transmission is disassembled.

Leejr57 wrote:however radiator has a lot of sludge in it

By chance does this have dexcool in it?

sorry for the delay in responding, Yes it was the dreaded red anti freeze. Drain entire system, flushed it out, seems to be fine now. Thanks for your input.

The damage may have been done already.

www.dex-cool.net

Especially if a FLUSH wasn't performed. You're on borrowed time. Even after losing the DEX, you still have to mechanically repair what was damaged. In this case, you're needing a LIM gasket replacement.

I disagree WillWren, there is no solid proof that his LIM gaskets have been harmed. I respect your authority as an Admin and knowledge as someone that has worked on many cars, however we can't say 100% every car or gasket that saw red coolant is on borrowed time. He only says red coolant, doesn't say it was factory GM Dex. And even at that, it hasn't been proven 100% that Dex is the gasket killer. Bill Buttermore and myself have proven that the nylon gaskets can and do fail in 30-60K without ever having Dex present.

A cooling system pressure test would be a good way to test if the gaskets or radiator cores have been compromised.

The fact that the car is a 93 and was shipped with phosphated green coolant to which Dex was (probably) added could explain the brown sludge that results from such mixing. If oil coolers within the radiator are found to be OK, and an internal coolant leak remains, I would suggest the most probable source is the LIM gaskets.

There is a lot of evidence that the use of Dex contributes to the failure of plastic-frame LIM gaskets. Because the gaskets in this '93 have probably been exposed to Dex, and the fact that they are now 16 years old, is reason enough to consider changing them out before they fail and cause serious engine damage. It's too bad that aluminum-frame gaskets are not available for the Series I engines.

I agree 100% with the comment directly above.

And Boosty, Buttermore's own gasket failure was not coolant-related. That's being hashed out offline and will come public when it's ready.

I have enough evidence in gaskets in my own posession that show a definite link with gasket failures and DEX. And just as much supporting evidence that green is far less harsh.