Engine Running and No Coolant Cap (Safe?)

Most guys won’t use one enough though including myself. I have robin Air vacuum pump for A/C under bunk used it 3 times in 4 yrs. different story. Is this the same tool used to hold coolant while changing a bottom hose? That might justify purchase for me. I’ve ony heard of such thing never used or saw one.

 

fwiw i drove a 12 mack pinnacle (mp7) almost 600 miles with no cap on the coolant reservoir. if i didn’t know it was gone to start with i never would have known. coolant temp was stable, as usual and none escaped the system.

 

I once got this loner truck. ProStar with an ISX.

So I'm doing my pretrip.

No cap on coolant reservoir.

So continuing on, hey there's the cap on the fender cover, passengers side.

So, open the compartment on under the sleeper on the drivers side, dude has like 6 gallons of water in there. Then find 2 more gallons in the passengers.

Going "Just wow."

So, replace cap, drive to Flagstaff at like 78,000 pounds in June, like 110 out.

Never uses a drop of coolant. Get back to yard several days later and leave the 8 gallons of water there.

 

After doing any sort of cooling system work that requires draining it, could be a rad replacement to just a drain and refill. I then fill with a 50/50 mix antifreeze and distilled water. Start truck with no rad cap on, cab heat set to full hot, and hood up, let it idle and as the coolant level drops keep topping it off. Once the thermostat opens and its done getting the air out, top it off again, put rad cap on and done. I should add i also drain the expansion bottle and refill it with 50/50 to about 2/3 full. As it cools off when you shut the engine off, it sucks the coolant it needs from the expansion bottle as long as the cap is on.
I also do not reuse rad caps, if it was time for a new rad or new hoses and a drain, it was time for a new rad cap as well.

 

I do that on my personal vehichles if i have to replace water pump, radiator, or drain the coolant etc.. After fixing it and fillin it back up idle without the cap on park car where front is higher than back or put it on a jack and it gets all the air out of the system,, aka bleeding the system.... Never done it on a big truck though

 

I know this post is old. However, I think or hope I got air in my system.
I drained all my coolant replaced a few lines etc. When I refilled it I didn’t run it without the cap, run the APU, heat or nothing!
Nevertheless drove about 100 miles, used APU and was about gallon low. Then today I’ve had to stop a few times per coolant low light. Added about 1/2 gallon each time.
Weird thing is that once I remove my cap the coolant rises way back up above the sensor to around the min cold line. Could this be air in the system??

 

Sounds like air. If the level doesn't balance out after a day or 2 I'd start to worry.

When I drain out coolant I like to try and ballpark estimate how much I got out of it. Then when I go to refill it I can kinda gauge how much it will need.

 

Appreciate it, ima keep adding and maybe try to idle a while without the cap and hopefully this solves my issue.