Filling Coolant with Block Empty

What’s the proper procedure to fill coolant when the engine block has been drained?

My capacity is 12.6 quarts and I got about 10 quarts out (assuming some is still in the heater core).

If I fill the radiator is enough coolant going to get into the block through the lower hose? I feel like the block will be starved for coolant until the thermostat opens.

Also, my repair manual says to fill the radiator with the air bleed open then to replace the radiator cap, close air bleed, and monitor coolant levels after driving. The video guides I’ve watched online show people running the engine with the radiator cap off until the thermostat opens and then topping off while the engine is running. Is this the proper/safe way?

Thanks.

Yes.

Just fill the radiator until full, start the engine and add coolant as the engine heats up.

Tester

Premix your own or use a premix. Do not try to pour some full strength and then some water (distilled), you won’t get it right.

Turn the temperature dial on the heater to high to open the heater valve. The bleed valve is located behind the thermostat at the top of the engine so as you fill the radiator, you will fill the block and heads completely. The top of the radiator is higher that the top of the engine so as soon as you see coolant coming out the bleeder, the engine is full so close it. Then finish filling the radiator.

Add some coolant to the overflow container but only to the min level. Start and run the engine until fully warmed up, then shut down and allow to cool completely. You can drive around if you want or need to, even drive to work if necessary.

After it has cooled down, check the reservoir to see if there is any coolant in it. Fill back to the min if needed. Then on the next drive cycle, check the reservoir while the engine is warmed up. Fill to the max level if needed.

Check the coolant level on the next couple of drive cycles. DO NOT operate the engine with the radiator cap off.

I wouldn’t run the engine with the cap off waiting for the thermostat to open. That likely lead to a considerable amount of coolant flowing out of the radiator.

Have you located the air bleed? If so fill the radiator and give the air time to escape through the bleed hole to allow the level to drop then add more. Repeat until the coolant level no longer drops and if you have added more than 9 quarts (based on your figures) close the air bleed, it should be safe to start the engine and run it till the top hose is hot to indicate that the thermostat is open. Allow it to cool until the top hose can be squeezed easily to ensure there is no pressure then open the cap and top off the coolant.

Operating an engine with the radiator cap off waiting for the thermostat to open is very poor advice.

Year, make, model and engine type is always useful when seeking advice though.

Let me add that YouTube videos do not have editorial or peer review. Anyone can post just about anything, they don’t have to be correct. The same is somewhat true here although if one member gives bad advice, the other members will be on him/her like fleas on a dog, so we have some peer review.

Your service manual comes with both editorial and peer review. Sometimes the service manuals are written for experienced mechanics so they can can be a little difficult to interpret sometimes if you are not an experienced mechanic so sometimes we can help with that here.

I guess us mechanics who have filled cooling systems with radiator cap off and the engine running for all these years have been doing it wrong?

Tester

1 Like

I guess us mechanics who have filled cooling systems with radiator cap off and the engine running for all these years have been doing it wrong?

Tester

Tester, still living in the 60’s?

A cooling system’s a cooling system.

Be it from the 60’s or today.

Tester

No they are not the same. Most are reverse flow now, we didn’t have bleed valves back then which is why we left the cap off after initial filling. BUT, the bottom line is that his service manual says to put the cap on. I prefer to follow the procedures outlined in the service manual. (most of the time)

Keith,

You make me laugh. And when showed my son your comment, who’s also an auto tech, he walked away shaking his head laughing, and saying, “What the hell does the flow direction have to do with anything?”

Tester

It was important to the engineers. By reversing the flow of coolant through the engine, it allows the engine to run a little hotter and have increased compression ratio. That results in greater engine efficiency and HP. That’s what the hell the flow direction has to do with anything.

I don’t think I should pre-mix the coolant. I know the capacity is 12.6, so I should put in about 7 quarts of coolant and then top off with distilled water. Whatever is left in there is all tap water; I flushed the crap out of this thing.

Oh, it’s a series one 3800 v6.

I have to side with @‌Tester on this one

I wasn’t wrenching in the 1960s, but I occasionally fill the cooling system with the engine idling

Per 2007 Honda Civic shop manual (using Honda premixed coolant):

  1. Fill coolant reservoir to MAX.
  2. Add coolant to radiator to base of filler neck.
  3. Loosely install the radiator cap.
  4. Start engine; run until radiator fan comes on.
  5. Turn off engine and add coolant to radiator if needed.
  6. Tighten radiator cap.

And then there’s those systems with pressurized coolant reservoirs…

I’m not a mechanic but having owned several series I 3800s, if he already flushed the thing so its filled with water, I guess I would agree to not use the pre-mixed stuff. He’d never get the concentration correct. On a car without the radiator cap, I have also filled it through the upper radiator hose first to try and remove the air out of the system, then back to the “overflow” bottle.

Is there a point to letting the care idle to temp (mine took almost 15 minutes)?

Why not just take it for a quick five minute drive?

You can do it that way, but I prefer to premix before filling, but then I never flush out a system. I have found that flushing a system that is working to cause more harm than good. Obviously if a system has been neglected so long that there are problems, then flushing or some other type of action is necessary, but other than that, no flushing for me.

Now that you have flushed it, which you didn’t mention earlier, you may be better off by adding the coolant first, but I would still mix some water with the coolant to start off with. Maybe mix 7 qts of coolant with 2 qts of distilled water and fill the system, save some mixed for the overflow. Top off with distilled water.

BTW, leaving the cap off while warming up the engine wont hurt it, at least not in the hands of a pro. But its not the right way to do it and it is not in accordance with the instructions in your service manual. I would never tell someone to ignore their service manual, even though on occasion, I may not follow the procedures exactly myself.

What I’m doing specifically:

I did four fresh water warm up and drains until I got pretty clear water coming out of the radiator (I had trans fluid in the coolant).

I pulled the radiator and removed the thermostat, then put a garden hose in the thermostat opening and flushed it out the bottom hose.

In about 30 minutes I’m putting in a new radiator and am going to fill.

I wanted to pull the block plugs, but I have to remove the knock sensors to do so. I assumed I would just be asking for trouble on a 25 year old engine.

Well, transmission fluid is oil and oil floats on water, so I doubt that there is any transmission fluid in the block. There should be a block drain somewhere that is just a bolt and gasket, like the oil drain plug and it may be located just below the lower radiator hose, but by now, there is probably nothing but water and maybe just a little residual antifreeze which won’t hurt anything.

Pulling the block plugs (aka freeze plugs), nothing to gain, everything to lose. You are right to leave them.