Engine reversing water to the over flow container

Question

I have a 1999 Pontiac Montana Van. The radiator fluid is backing up to the over flow container.

So,what can be my problem?

I put new thermostat in and flushed the radiator.

Are there any additional troubleshooting steps I can enact to discover what the problem is?

It could be the radiator cap. These are pressure rated (16 psi in your case) and when they get worn they can allow it to overheat and/or bypass to the overflow. This is a cheap troubleshooting items since they are usually under $10 and can solve a lot of cooling issues. — CharlieRB, Aug 11 '16 at 20:15
@CharlieRB - I'd put my $10 on a radiator cap first as well. A heck of a lot cheaper than jumping right to a leak/blown gasket. Good call. — Pᴀᴜʟsᴛᴇʀ2♦, Aug 11 '16 at 22:22

Moab · Accepted Answer · 2016-08-11 20:08:04Z

2

More than likely it is a head gasket leaking or a cracked cylinder head.

You can use a combustion leak detector to find out if it is the exhaust gases leaking into the cooling system causing your issue.

answered Aug 11 '16 at 19:59

Moab

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