Coolant Reservoir Fill Line - What is Ideal and When? (1 Viewer)

[VinylSeats]

Hey all. I've searched through a few threads regarding ideal coolant level but many of them discussed peripheral issues related to coolant, not my primary question.

What is the ideal level of coolant in the reservoir and when?

I have a 1999 with 260k on it. I had a shop replace the radiator about 1,000 miles ago. I did not inspect the reservoir to see coolant level immediately after the job.

The other day I looked at the reservoir completely cold (had not been driven in 24 hours) and saw the level at an inch above "Low."

I drove the truck to work today (7 miles, ~20 minutes) and viewed the coolant level when I arrived to see it right between "Full" and "Low," a small bit closer to "Full."

From reading the manual, I can't tell if coolant in the reservoir should be full or half way full.

I don't think I have any type of leak as I've seen no evidence of it.

I suppose I should just confirm the coolant used by the shop and top it off to the "Full" line when the engine is cold?

 

[CJF]

There is no "ideal". Just like the manual says, anywhere between low and full with a cold engine is fine. (Level will rise as the engine warms, and lower as it cools.)

Personally, I do like to keep it right at the full line when cold. Makes a nice marker to easily check whether I'm losing any over time. (Even keeping it higher than the full line won't hurt anything; you might just purge a little first time the engine warms up.)

 

[flintknapper]

There is no "ideal". Just like the manual says, anywhere between low and full with a cold engine is fine. (Level will rise as the engine warms, and lower as it cools.)

Personally, I do like to keep it right at the full line when cold. Makes a nice marker to easily check whether I'm losing any over time. (Even keeping it higher than the full line won't hurt anything; you might just purge a little first time the engine warms up.)

^^^^^^ Exactly.

In fact, I keep the coolant level (when cold) about 2" below the top of the reservoir on both my LX and 80 series.

I used a black permanent marker to mark the fluid level. Easy to see.

Upon engine shut down (really hot days) the fluid will be near the top but I haven't had it overflow. Even if it did it would just purge a small amount.

 

[Eltestro]

^^^^^^ Exactly.

In fact, I keep the coolant level (when cold) about 2" below the top of the reservoir on both my LX and 80 series.

I used a black permanent marker to mark the fluid level. Easy to see.

Upon engine shut down (really hot days) the fluid will be near the top but I haven't had it overflow. Even if it did it would just purge a small amount.

I know this is an old thread, but how does it “purge” itself? Just out of curiosity.

 

[oakback]

Leaks out from under the reservoir cap, I'm pretty sure.

 

[flintknapper]

I know this is an old thread, but how does it “purge” itself? Just out of curiosity.

The pics posted below are from my 80 series...but the concept is the same for all 'Overflow' reservoirs (not the same thing as an expansion tank).

The Overflow Reservoir works in conjunction with your properly operating radiator cap. The purpose of the reservoir is to hold expanding coolant (rather than have it dump out on the ground) and then allow it to return to the radiator as the system cools.

Without going into a detailed explanation concerning the necessity and function of a radiator cap, suffice to say it is basically a relief valve (2 way).

When the coolant temperature/volume (related) reach a prescribed level...the radiator cap valve opens and allows the fluid to expand into the Overflow reservoir. When the engine cools...the fluid volume in the radiator (cooling system) becomes less, creating a vacuum. This vacuum draws a certain amount of coolant from the Overflow Reservoir back into the radiator.

This happens in a 'circuit' comprised of the hose coming off the radiator, going into the reservoir cap and then to the bottom of the reservoir via another hose. That circuit is separate from the discharge hose (which expels/purges air and excess fluid). So if you overfill your reservoir when cold and the expanding fluid from radiator travels to the reservoir, any excess will simply flow out the discharge hose since it is open to atmosphere. There is a hole in the underside of the reservoir cap that allows this.

 

[Eltestro]

Leaks out from under the reservoir cap, I'm pretty sure.

Gotcha thanks.

 

[Eltestro]

The pics posted below are from my 80 series...but the concept is the same for all 'Overflow' reservoirs (not the same thing as an expansion tank).

The Overflow Reservoir works in conjunction with your properly operating radiator cap. The purpose of the reservoir is to hold expanding coolant (rather than have it dump out on the ground) and then allow it to return to the radiator as the system cools.

Without going into a detailed explanation concerning the necessity and function of a radiator cap, suffice to say it is basically a relief valve (2 way).

When the coolant temperature/volume (related) reach a prescribed level...the radiator cap valve opens and allows the fluid to expand into the Overflow reservoir. When the engine cools...the fluid volume in the radiator (cooling system) becomes less, creating a vacuum. This vacuum draws a certain amount of coolant from the Overflow Reservoir back into the radiator.

This happens in a 'circuit' comprised of the hose coming off the radiator, going into the reservoir cap and then to the bottom of the reservoir via another hose. That circuit is separate from the discharge hose (which expels/purges air and excess fluid). So if you overfill your reservoir when cold and the expanding fluid from radiator travels to the reservoir, any excess will simply flow out the discharge hose since it is open to atmosphere. There is a hole in the underside of the reservoir cap that allows this.

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Thanks very helpful!