1990 5.7L Chevy leaking coolant behind the block

[sw99]

236K on the Blazer. PO said the 350 was rebuilt approximately 40K ago.

Got it out for a test run on the highway to break the gears in... Parked it and noticed it started to spew coolant from the back passenger side of the block area. First I thought it was a core / freeze plug but after pulling the starter it was not. Started it up and the best I can tell is it's coming from up behind the block. My thought now is possibly the intake manifold gasket?? Never delt with this before but it seems like quite a decent leak for just a gasket? I did rule out the hoses and the heater core fitting on the back of the manifold. Could it be possible to dump a lot of coolant from the manifold gasket? I just cant imagine what else this could be. Any thoughts?

My next task will be to get an inspection mirror to see if I can actually isolate the leak. Also I did check that there is no coolant in the oil or oil in the coolant.

Thanks folks!

 

[Warstud]

Get some UV coolant dye.

 

[05GMC]

there are 2 freeze plugs behind the flex plate on the rear of the engine , could it be one of them ?

 

[46Harry]

I would suspect one of the two freeze plugs at the rear of the block are leaking. If that is the case, either the engine or transmission will have to be removed to get at the plugs. It's possible that the intake manifold is leaking at the back if the manifold wasn't installed properly, but usually coolant leaking at the rear of a Chevy small block is because one of the freeze plugs has failed.

 

[KenO]

Lower intake manifold gaskets. They typically leak in the back, and leak down the back of the block/bellhousing of the trans. I just did this on my truck. What an absolute nightmare.


Wait, I see in your sig it's a '90.....So a TBI motor, not a Vortec? Hmm, might not be an intake gasket leak then, I know that was one of the biggest issues with the Vortec 350.

 

[morepwr]

I would bet intake gaskets but also look at the heater hose connector on the rear of the manifold on the passenger side of the distributor. They are known to corrode and cause leaks. Best way to fix is to just put a regular fitting there if that is the source of the leak.

 

[Oldswagon]

Originally Posted By: morepwr
I would bet intake gaskets but also look at the heater hose connector on the rear of the manifold on the passenger side of the distributor. They are known to corrode and cause leaks. Best way to fix is to just put a regular fitting there if that is the source of the leak.


I second this, the heater hose quick connect is my number one suspect, followed by intake gaskets. My old 5.7L quick connect literally fell apart. I made up a new heater hose connector with a brass NPT nipple. Either job is an easy DIYer job for anyone with decent mechanical skills. Both are pretty cheap fixes too.