Possible HG leak?

[FL85GrandPrix]

OK, finally went through this car I got about two months ago. Completely stock 85 GP 5.0 with Qjet computer carb on it. Car has 95k original miles, bought it from the old lady with a box of records. All the plugs that came out went back in, they all looked great, just adjusted the gap. I bumped the timing to about 6-8*. Had the radiator repaired (soldered) by a local shop. I did an oil change on it also. I've been running the engine and letting it warm up and drive around the block, but no actual driving since I bought it. I've been flushing out the cooling system and am starting to get worried. The overflow tank is all sludgey. So I disconnected it for now. I'm getting a brown rusty oily goop after warming it up. Each time I do a flush and fill it's less and less each time. I did flush it out for 2 days with 1 gallon of vinegar and warming it up a few times.... man did that flush the system out. The oil looks squeaky clean, the crap in the radiator is a brown oily sludge that is floating to the top. I figured if I was getting oil into the coolant, it would not be brown rusty looking sludge, it would be the clean oil I have in the engine. Car runs great, has no other signs of a HG issue. I have a feeling the oil lady or an idiot mechanic dumped oil into the overflow tank at some point. Plugs, compression and oil look spot on. Again, seeing some minor rusty looking gunk float to the top of the radiator water..... It's either a HG or I knocked some crud loose! Looking for some fellow input.

 

[L67ss]

I'd guess it was from running coolant too long in between coolant flushes. Or even just running straight water too long. I'd swap out t stats and water pump

 

[lilbowtie]

Pull the cylinder block water plugs and drain and flush it there. There is probably so much gunk in the block it won't drain when you pull the plugs.

 

[pontiacgp]

I wonder if the transmission cooler is leaking into the rad...

 

[64nailhead]

Putting water in the block and trying to flush repeatedly is going to lead to more rust (crappy) looking coolant. Pull the block drain plugs and flush 5-10 gallons of water through it. Once it stops draining, then refill it with an ELC. Run it upto temp and recheck.

The issue you have is that the water is continuing to rust the block and heads. An ELC will protect the metal and eliminate the rust in less than a couple of hours.

 

[FL85GrandPrix]

I did put a new Tstat in it, went with OEM temp of 190*F IIRC. Water pump is relatively new and not leaking so I left it. I'll pull the block plugs and see if I can get it to drain that way.... Yeah, it's looking like just a neglected cooling system more than anything. OH, and the heater core valve was in crap shape so I pulled it out completely. New heater hoses, no valve. Sounds like I'm doing another vinegar flushing round. I went through this, just not as bad, on my '89 K5 project. However that trucks heater core was leaking so I replaced it and the radiator was also replaced with a new, so I was able to run a few flush sessions with no tstat and then I put it in. I installed a spin-on coolant filter kit on the K5, which the plan was to do the same on the GP once the "flushing" was done. I might pull the Tstat out of the GP and do a few rounds like that then re-install it.

 

[FL85GrandPrix]

update. pulled the tstat out. Flushed the crap out of the system with a hose. Tstat needed to come out or I was never going to get this thing cleaned out. Ran the engine with the hose in the filler neck, radiator petcock pulled. That really flushed it out. Also disconnected the heater core and flushed it directly with the hose in both directions and reconnected. Then I took a 5HP shop vac and sucked everything out through the top radiator hose. Could not believe how much water and crud that thing pulled out. System is clean.... I just had a very dirty cooling system and I was seeing rust crud floating. I'm sure I could keep flushing 999 more times, but I've been working on flushing this system for 3 days now. I don't see it getting any cleaner without another vinegar flush and driving the car for a few days. Problem is it's not tagged and I don't drive it... garaged. So it's good to go. The 5HP shop vac actually worked VERY well. First time I've done it, have to remember that one. Now I know I don't have 1 or 2 gallons of water in the block when adding my premixed 50/50 antifreeze.