Can I change the oil to this one

KHIDREAL

MEMBER
1998 PEUGEOT 306
1.8L
4 CYL
2WD
MANUAL
150,000 MILES

Hi.

My car should have every had the multi grade oil 10W-40, recently I put 15W-40 on it and the car got problems cold starting during cold days.
the engine is old and I wanted it to get lubricated more, to get that rust and dirt from places the 15W-40 can't reach.
So I went reading my owner's manual and suposedly, my car shouldn't have 15W-40, the only oils they recommend are 5W-40 and 10W-40.
I wanted to put in it 5W-40 as I believe it will be better for cold days because the engine will have less resistance to start and also because the 5W-40 will reach places the others can't.

so my question is if it's a smart idea to jump from a 15W-40 or if I should go to 10W-40 and later on go for the 5W-40.

Also, what do you think it's better for an old engine? A thick oil or a less thick oil?
I have heard both options, some people say that a thicker oil is better because the oil won't pass to places it shouldn't. But I also heard that a thinner oil is better because it will lubricate in places the other oils can't reach.
so what is best? A thinner oil or a more thicker oil?
and should I downgrade my oil from 15W-40 to 5W-40 (skipping 10W-40 in the process)?

thanks.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi and thanks for using 2CarPros.

I strongly recommend not using 15-40. That is too heavy. As far as the options from the manufacturer, 5w40 or 10w40, either is fine. However, if you are in a cold climate, the 5w40 is recommended. Both oils will maintain the same viscosity when hot, but the 5w40 will make for easier starts and allows the oil to get to places faster.

Now for more interesting info. The 5w40 will not be available in a conventional oil, but rather will be synthetic; where as the 10w40 is available in both. Conventional oil is cheaper.

Lastly, it will not hurt to go from the 15w40 to 5 or 10w40. If the temperatures are cold, I recommend doing it and not waiting. It takes longer for the heavier oil to circulate in cold weather which in turn causes more damage to bearings and other components in the engine.

If you have other questions, let me know.

Take care,
Joe

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Monday, March 4th, 2019 AT 6:10 PM

KHIDREAL

MEMBER
11 POSTS

Joe,
Thanks for your reply, it cleared my mind and put some peace to it. In my country every oil is synthetic, it's not very commom to find mineral oil (common oil).

I have another question:
I live in a country that is fairly between -5� C (23� F) minimum during the winter and 40� C (104� F) at maximum during the summer. Even during summer times, should I keep the 5W40 or should I put 10W40 for summer and on winter go back to 5W40?

Also, yet another question, a 5W40 will reach places the 10W40 can't, but the 10W40 is thicker and despite not reaching every single place will offer more protection to the moving parts are they will have a thicker oil between them, creating less friction.
What is your intake on this for a twenty years old engine?

Thank you once again.

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Tuesday, March 5th, 2019 AT 7:01 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

During the cold times, use 5w40. When it gets hot, you could use either. Here is what to remember. The 5w40 will circulate faster, especially when it is cold. However, both oils will offer the same thickness when hot and both will reach all areas. Once just does it faster when it's cold.

Let me know if that helps or if you have other questions.

Take care,
Joe

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Tuesday, March 5th, 2019 AT 6:50 PM

KHIDREAL