Significant coolant passage blockage: my plan?

Steve McMahan · Feb 27, 2025

On my 5.0 from a 87 TBird, I pulled the lower intake off today and found the rear water crossover 100% blocked. I chiseled out what I could, but I can see some significant loose crud inside the rear of the heads.

I don’t want to remove the heads, so I thought, what if I removed the rear freeze plug at the rear of each head, and using the front coolant passage as the inflow, flush the heads out? I have a complete set of freeze plugs I was going to change out, as one has a slow weep. Bad idea, ok idea, good idea (pick one). I also had a broken stud at the same location, got it off with the welder and a nut.

Thanks for your time and support.

rvrtrash · Feb 27, 2025

You undoubtably have the same level of crud all through the cooling system. I would seal it back up and run some radiator flush chemicals through it, and then check to see if it's clean. If that doesn't work, take the engine apart and have it tanked. If you have to do that, don't forget the heater core and radiator.

giantpune · Feb 27, 2025

you got the engine on the stand where you can flip it over. I'd rotate it so the head is oriented in a way that you can fill it up and it'll hold. Then fill each head up with evaporust or something. Let it sit and work. Then flush it out with a hose.

Steve McMahan · Feb 27, 2025

Great idea @giantpune, I’ll try that.

Steve McMahan · Feb 28, 2025

I did as you suggested, @giantpune. I’m using that Home Depot concrete etching stuff, and it’s making burping sounds, etc. So, two questions. 1, how long do I keep the stuff in there, and 2, how would you recommend I remove it (assuming you’re living in an HOA, and you don’t want to run that stuff down the gutter)?

I was thinking, remove those two small block plugs, and drain the block. Then, remove all of the freeze plugs, and clean it out as best I can. I’m gonna do it on a HF moving blanket to catch the crud.

giantpune · Feb 28, 2025

No clue on how long to leave that stuff in there. I haven't used it.

To get rid of it, I'd just put a plastic tote or bin under the engine, then rotate it over till the stuff started pouring out some of the coolant holes. Once you get most of it out, drag the thing outside and blast it with the garden hose. As the shampoo bottle says, rinse and repeat.

Steve McMahan · Mar 1, 2025

I was able to get the stuff drained, and I removed the 6 freeze plugs (one had a slow weep), and using my power washer, I got it very clean. Better than I thought I would. I had a couple of handfuls of gravel come out of it. The topside, lower manifold segment was also plugged, and the throttle body heating segment was also plugged. So, all in all, a successful cleaning. Thanks again for the helpful advice.