Can a leaky coolant cap cause increased water temps?
 

Just replaced my coolant cap which was leaking very slightly. Was the original cap from '97 with the .00 part number. New part is .04.

Thought I noticed higher operating temps recently, which is what hand me sniffing around the cap. Nothing absolutely dramatic - normal temps on the cruise, but was quicker to build heat and spin the fans up in stop start traffic.

Haven't had a chance to fully test the new cap, but was wondering whether a leaky cap and presumably some pressure loss would push up operating temps a bit?

My coolant cap does not leak but its goes up near the second notch after the 180 on stop and go traffic and goes back near 180 on cruising speed I guess thats normal.. Maybe the new cap 04 is an updated version. ;)

The new cap (-04 is the latest) should hold pressure better (assuming no other system issues), which would raise the boiling point of the system and nothing more.

You should also be aware that the dash display is notoriously inaccurate and nonlinear, so “splitting hairs” over where the needle sits is a waste of time. You should look at the dash gauge as telling that the car is either “hot” or “not hot”, and nothing more…..

I'm not using the dash display, though once you learn it, it's not that bad at all, you just need to know how to read it. I'm using the climate panel to read the actual coolant temp via the hack / codes.

It's really hard to be sure re the operating temps. All I know for sure is that it's fine when cruising and that the fans operate normally and cool reduce the temps as before. What with variable conditions (it's summer now, so higher ambient temps), I may be imagining things. But I don't think so.

Because some have found significant discrepancies between the OBD II data and the climate display, I have not had any confidence in the readout accuracy of the climate panel “hack”; we go by reading the actual coolant temperature over the OBD II port using either a quality scan system or a data logger, which has been confirmed accurate.

OK, all I can say is that it seems accurate to me. The fans trigger at exactly 108 degrees on the climate panel. Never any deviation.

In reality, the important thing isn't the absolute number. It's consistency. If it always displays a certain number for a given temp, then that's all you actually need.