<!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> I have a coolant leak on my 1997 GMC Savana 5.7L on the back of the engine. It seems to leak only a couple hours after sitting, say overnight. It hesitates when I hit the gas after it sits. It also has a bit of a popping sound in the exhaust. I got a Check Engine Light that the trouble codes were PO171 and PO174.

I changed the thermostat thinking that is what leaked, but it wasn’t. I replaced the fuel filter and it still hesitates. Is it the lower intake manifold and would that leak coolant?? Also has anyone changed the intake gasket themselves??

I have done a video showing everything in detail: 97 GMC Savana Coolant Leak on 5.7L - YouTube

If you have any questions or need clarification, do not hesitate to ask.

Thank you for any help.

 

Those codes are O2 sensor upstream, both sides. Is there any white smoke? Also I cannot tell from the video if it is the intake or head gaskets. Zoom in better so I can see. The head gasket would cause an O2 sensor to give false readings, and both sides leaking if it is a head gasket would explain that. Has the engine ever overheated? What has changed?