Hey all, doing the chore that I can't stand, rather be tearing the doors apart and re-aligning windows.
Yes, coolant burp time. Last time I did this, a dumb mistake burnt the crap out of my hand and several other spots on my body (luckily, not my face or eyes!). Hate it.

Anyway, items in place to make it "easier":
1/8" hole in thermostat
Nice incline and 2x4 to get a little more.
Open ears for more.

Problem so far:
I did a cold burp by no belt and spinning the water pump fast, while my son filled. Typical, level swooshed down, fill, etc.
Then heated up the engine, drove a bit and let cool over night. Filled radiator (no start) and repeated a couple of times.

Now to the odd part. All that, coolant looks good in radiator but there is zero overflow into the recover tank.
Today I went a full burp, after removing a few cups worth to prevent the first overflow and so forth. Filled, let run until aux radiator fan started kicking in, heck even ran at 2K for a minute of so, trying for HOT. Still zippo pushed to recovery tank! Didn't even put all the fluid I removed back in!

Prior to the burp, thought maybe the radiator cap was toast, but it tested fine at 16psi.

What am I missing here? All I can think of is tons of air in the water, but that makes no sense. Top hose is very firm when running. There should be enough pressure to pop the cap!

I really hate coolant change.

PS. '87, in case you didn't notice. Stock.

 

Perhaps you have a little leak somewhere?

 

After it sits overnight, fill your overflow reservoir to the "full cold line". The reservoir is part of your "coolant capacity", your cooling system will pull or push antifreeze back and forth with expansion/contraction, if your reservoir is empty, it will only suck "air" back in. I usually drive my C4 up on ramps for coolant change, this effectively makes the radiator cap the "highest point" of the cooling system and helps the air get out. Back in the day, brass radiator tanks would have a molded line on the side below the cap, indicating the "full" line. This was when the overflow nipple/hose vented to the ground. But with an overflow reservoir, I fill the coolant right up to the cap flange, you don't want any room for air/expansion in the radiator, that's what the overflow reservoir is for! Top of your radiator again, fill reservoir to full cold, go for a good drive, watch temp, on the highway your temp should be at or below your thermostat temperature (that's how you'll know the thermostat opened. A "firm" upper radiator hose usually indicates a thermostat that hasn't opened yet....with someone else revving your engine when temperature is at or about thermostat temperature setting, squeeze the upper hose, it should go from firm (good and warm) to the feeling of collapse under the tension of your grip and get very hot, it is right then that the thermostat opened! Good luck 👍

 

not to be captain obvious, but have you confirmed the hose to the expansion tank free and clear? I've had that hose gunk up on other cars preventing flow to the tank.. and I don't get your 'cold burp' manual spinning water pump fast, isn't that the same as a engine running on a cold start? stop punishing yourself.

 

Just How old is your Radiator Cap? They do go "bad" and could do what you are describing. The original radiator Cap on these L98's was 16 pound radiator cap. Any auto parts store should have a 16 pound Radiator cap.

To have a functional "Overflow System" in the cooling system you need a good radiator cap and good tubing between the cap and the Overflow bottle. When the engine is cold you should fill it too the brim of the radiator and fill the overflow bottle with it's Minimum Level of coolant. Then secure the radiator cap and let the engine warm up and see if the overflow starts working properly. As the engine warms up it should push coolant out and when she starts cooling off it will pull the coolant back into the radiator from the overflow tank.

I have never had to do anything special to my L98 to get the air out of it. And mine is a 1988. I replaced the radiator one time and the filling was non problematic. I replace the Radiator caps on all my cars at 10 years, coolant every five. I have been debating on replacing the overflow line every ten to be sure I don't hurt my engine. I just don't understand why some L98's are hard to burp and others have no issues at all.

My daily driver is a Buick and it has air release holes where you can open the vent and let out the air and it is Bled! The overflow system works the same as the Corvettes. If you don't use the overflow system then likely your radiator has a bunch of air in it. The engine will push out the excess coolant but if it can't pull it back then air is pulled in place frequently. Without a functional Overflow system your engine will likely run a bit hotter as well.

In the future I might suggest using a infrared thermometer to check for heat. If there is even a chance of a spraying fluid I wear a face shield and use heavy gloves.

 

I would agree with '78-- fill your overflow to "cold." The system is designed to be self venting form what I've read, but an empty overflow can introduce air. Ditto with the line from tank to overflow--blew up two radiator hoses all because the line was blocked to my overflow on my Miata.

Hope that helps

Ronn

 

The only car that I had to do anything exotic to "burp" it was a Gen 1 Viper where the radiator cap literally sat below the engine height. By 96 they had corrected this.

 

I invested in one of these a while back: . Of course there are other brands that work equally as well, so you do have choices if you decided to go this route. Ebay is a good source to to get one cheaper. Works on all of my GM cars including the '86. I have never had an issue with air trapped in the system of any of my cars after a drain and fill. It actually makes refilling a one and done job, and was well worth the investment to me.

 

Yeah, I checked the hose. Then I didn't trust it, maybe it had gunk inside that only clogged at a certain position. Replaced the hose and cleaned the tank just for an extra $.02. No change from that.

And yes all, expansion tank filled to cold and a itty bit extra. I replaced the cap sometime in the last four years, I forget. Tested fine the other day. Think maybe the upper seal is the problem? I wrapped a paper towel around the cap with a rubber band during a drive to make sure it's not leaking anything, stayed dry.

Key is when I check the radiator, typically expect coolant to be right at the rim. So far, every time after at least ten miles of driving, there's about a half a cup of air space instead. Don't notice air sucking in when I remove the cap.
And no, no leaks noted.

Maybe I'll worry about it after another 250 miles. Half way through the break-in!

 

Mine has never pushed coolant into the overflow tank unless it’s gets to 210-220 degrees. At normal operating temp, it will not push coolant out.

I don’t think you have an issue.

 

this is the real issue, not the burp procedure and up on ramps should be enough.

yes, there's a leak

How old is the radiator? and is it the plastic end oem style?
Pull all 8 spark plugs, see if any 1 or 2 are 'clean' which will indicate head gasket leak
Pick up coolant dye, I have this, stuff is great very strong, don't even need a UV light for big drips, but use a UV light to see the small leaks.
Pick up a radiator pressure tester, see if cooling system holds pressure, but it already seems like it doesn't

That OEMTOOLS 24444 is great to have, I used it on my BMW E36, in this case not needed imho

 

Mine will start pushing coolant out of the radiator before hitting 200*. It starts a little before that on my 1988.
I have a replacement radiator and have never had any air trapped. I do believe that my front end was a bit higher when I filled it last.

Is your radiator a stock one or replacement? What brand if it is a replacement? I am going to test my radiator by using a Differential Display with two temperature senders. One will at the top (inlet) hose and the second will be on the outlet. This will let me calculate how well the radiator is working. It would be interesting to see the results.

Usually after thee or four cycles of heating up and cooling down should have the system working like a charm. That is the way they designed it to work.

Beware that there are some Radiator Caps that need to have the arrow pointing towards the hose to the overflow tank. If not pointing at the overflow hose it would not let the coolant flow to the overflow tank. Be sure that the latch is pressed down if the cap has one built into it.

 

Dang, guess I'll go rent the radiator pressure tester again, didn't consider a leak somewhere in the radiator or block, only tested the cap. I'm at 250 miles on rebuilt engine break-in, probably in denial.

 

I think it's autozone that will lend out things like the tester. Here's a tip if you use something like the yellow/green Prestone antifreeze. It will Flores under black light, which can be used for looking for indications of a leak. Pressure testing is a good way to tell if you have a leak but won't tell where it's at.