, I have a 1992 Bonnie 3800 that has recently started having fluctuating low pressure between 20 and 40 psi when idling and goes above 40 when I hit the gas and drive. On warmerer days 75+, Theres been times when the car will run rough and feels like it wants to stall. Also when Its runs that way, My coolant starts coming out of the resvior. I thought me car was over heating but me temp guage is reading fine.
Now I did have my Oil and oil filter change and I had put In 5w30! So Im getting a new oil change and filter change tomarrow. I read the forums and I see 5w30 Is a No No for old cars and those warm days. I had my last oil change done a month&1/2 ago and I started noticing it when the temps outside got above 55. I'm keeping my fingers crossed that this will take care of the problem.
Does Anyone see anything else it could be????? And what type of oil should I use for warmer days I live in Mn and its going to start getting hot!!
Should I try 10w40 15w40 or 20w40? Thank you for the help

Any Idea?

10w40 will be just fine, no thicker then that.

When your oil pressure drops do you here and tapping sounds? It is possible your pressure sender is going bad.

Nope, No tapping sound that I know of. There'* ticking noise on the driver side, But that I was told has something to do with my A/c. The neddle on the guage never hits the red so I have no dinging. Its just fluctuates at the moment. I'll have to check that out though If this oil change dont fix the problem.
I'll be sure to post if the oil change worked or not.

Its written on your oil cap 10w30... your just asking for problems when using 5w30 and it definitely a big no no.
Btw i use 10w40 to keep the gauge over the red bar