97 tahoe knock

[nhbluevip]

I have a 97 tahoe, with the 5.7, 4x4, two door. It has 148000 and has been great. Ive done alot, however only thing to the motor was new plugs, wires, cap, rotor, air and fuel filter. My question is, recently with the colder temps, 40's, when I start it cold, there is what sounds like a deep, lower end knock in the motor for about 30 to 40 seconds, then it disappears. I run Castrol high mileage 5w30 in it. Is my motor on its way out? It does not use any oil in between changes.

 

[steamroller]

What does the oil pressure gauge read on startup and which oil filter are you using?

 

[Biggwaukegan]

could be a knock sensor too. But Id bet you have a oil pump starting to go bad. Best to fix that asap. It cost me a new motor because I didnt pick up the problem right away.

 

[nhbluevip]

I have been using the napa gold filter. The oil pressure on start up hasnt changed either, it is always in between high and the middle which I believe is 40, and then after being driven and warm it settles to 40, or just below it. This has just started to happen since its gotten cold outside.

 

[steamroller]

I would just try a different oil, since the oil pressure is good it sounds like it may just be taking a bit for the oil to warm up. I'm not 100% certain but I think the high mileage oils are formulated to to not thin out as quickly as a regular oil. With newer engines the tolerances are much tighter than what they used to be 20-30 years ago, unless you have leaks that oil is unnecessary IMO.

My brother swears by the Valvoline high mileage on his 79 C10, but again that engine was built 30 years ago

 

[nhbluevip]

I will try a different oil. I dont know if that would be the case, but worth a try. I used to have a 92 suburban with 145000 on it, never lost any oil in between oil changes, and I always ran the high mileage oil summer and winter, and never had this knocking sound on start up when cold.

 

[retorq]

Could be piston slap.

 

[newmarketeod]

I have this same issue, although my oil pressure is never at 40 except for sometimes under hard acceleration.

 

[nhbluevip]

So does that mean time for a new motor? I also a few months ago did the seafoam treatment through the brake boost. I did change the oil after that as well.