Nasty coolant. Bad head gasket?
 

Truck is a 1988 cab and chassis with a 5.7l, fairly new to me. I changed the oil a couple weeks ago and it was clean and clear, no evidence of coolant. No overheating, no visible bubbles in the radiator or overflow bottle with the engine running. The truck does seem to use a little coolant, but it is leaking from the radiator cap and I assumed that was the only problem. I changed the cap with a new one today and we'll see if the leaking stops.

But the radiator is full of nasty black water like I have never seen before, but it is not "goopy". Its a low viscosity fluid like water/coolant should be. The exhaust does blow white smoke for 2-3 min after startup. The white smoke lasts a bit longer than I've seen from other SBCs in the past, but I thought it was just condensation until the engine warmed up since it did eventually go away.

Is a compression test my next step? Flush the coolant and see if it turns black again?
If anything, this looks like combustion gas leaking into the cooling system through a head gasket leak or head/block crack. But if that were the case, I would expect water to be spraying out of the radiator with the cap off and engine on...


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Re: Nasty coolant. Bad head gasket?
 

Things to check first are:

1. intake gaskets
2. heater hose connections
3. heater core

Add the plastic tanks on the radiator and those are the most common leak areas on that engine. I can't say I have ever seen a head gasket on a 350 go bad without severe overheating first.

Re: Nasty coolant. Bad head gasket?
 

What would the heater core and hose connections do to cause the dirty/cloudy coolant?

The truck is fairly new to me but has not overheated since I've owned it. No idea what the previous owner may have done to it though.

Re: Nasty coolant. Bad head gasket?
 

Change the coolant out and regill with plain tap water...run until hot wth heater valve open....

Drain water when cool enough to work on

Refill with fresh plain tap water and run until warm...pressure test with heater valve open....

The balck discoloration is most likely too much radiator stop leak in the system...usually to stop heater core leaks prior to sale....

If heater core is leaking you can bypass it until repairs.

Prior to daily driving, drain water and refill with fresh clean coolant....

Dont let your pets get anywhere near the drain off from the original flush or the subsequent flushes...or the coolant for that matter...

:chevy::chevy::chevy:

Re: Nasty coolant. Bad head gasket?
 

You'll know if a head is leaking into your coolant passages. One of the things you'll notice is if you crank your engine with the radiator cap off, it can spew water like a geyser. However, if it just slight leakage, you'll see bubbles forming in the radiator neck. Also, your radiator and heater core will over pressurize and could begin to leak. You may blow a radiator hose off.

Re: Nasty coolant. Bad head gasket?
 

Go to a parts store with borrow a tool program borrow the leakdown rad tester
Hook it up run pressure to about 15 lbs or so
Check readings over 1/2 to help see how far it drops
Do you smell antifreeze in the cab ?

Leaky heater core will not contaminated the coolant with oil

You can bypass the heater core retry leak down pressure test

Check for wet spots around the intake

Run the truck cold with no cap watch coolant for bubbling this is an indicator of a possible failed head gasket

Re: Nasty coolant. Bad head gasket?
 

If you're going to do this, make sure you drain the tap water and refill with coolant before Monday. We're going to have some more cold temperatures here.

Re: Nasty coolant. Bad head gasket?
 

If the PO never changed the coolant, possible things got pretty funky in the passages. I would do a complete drain, including the plugs on the side of the block and refill with fresh water. Then do your best back flush and see what comes out. Then run it and see what happens.

Whatever you do, when you finish, make sure the coolant is still freeze rated. Winter probably isn't done tossing cold spells.

Re: Nasty coolant. Bad head gasket?
 

A block tester is inexpensive, easy to use and effective. You might try one of those before you take the it apart.
https://www.google.com/search?q=bloc..._AUoAXoECAEQAQ
https://encrypted-tbn0.gstatic.com/i...Zp004&usqp=CAc

Re: Nasty coolant. Bad head gasket?
 

p
X2 do this first he is onto something
POs are notorious for doin stupid **** for a sale.