Truck Question - How much damage did I do?

1999 Chevy Subburban LT 4x4 that has been an amazing vehicle (200k miles) but I fear I may have damaged her, let me explain.

I have known for about the last 10k miles that I appear to have a VERY SMALL intake gasket leak. So small in fact that you can only tell when idling in gear (say at a stop light) and even then the untrained ear (like my wife) might not be able to tell. It also only throws a code (P0300) every so often.

I tell you this for reasons that will be clear in a moment (and yes I plan to replace the intake gasket soon).

About 6 weeks ago, in 50 degree weather I replaced my thermostat and did a coolant flush along with an oil change. All has been fine even in freezing weather until today when the temperature was sub zero for the first time this season.

I went out and started the truck while getting ready for work and when I came out 20 minutes later the temp needle was pegged and cold air from vents. I quickly shut the truck down knowing it was most likely not enough antifreeze in radiator

After the truck cooled off I drove her 20 feet to the garage warmed to 45-50 and a few hours later checked the coolant. It was then that I noticed two things:

  1. While I normally ALWAYS use pure undiluted coolant, I mistakenly used 50/50 diluted that I then diluted to 25/75 (thinking I was using undiluted 6 weeks ago during flush).

  2. The system was no longer full (probably 85%) which means that the small intake leak over the last 6 weeks had further weakened my anti-freeze protection.

Inspection showed no loss of fluid other than the overflow drain during the overheating so I am hopeful that I did not crack the block. After draining and filling properly with right amount of anti-freeze the truck started right up and sounded no different than ever.

Does the burb have freeze plugs in the block? If so how can I tell if they “popped”

I did drive 50 miles in -4 degree weather and the only thing I noticed was while my front heat worked great, the rear was blowing cool no matter the setting.

So I ask you, what damage might I have caused and what would you check/do to the truck to determine if there is any issue and to get that rear heat back?

1. While I normally ALWAYS use pure undiluted coolant, I mistakenly used 50/50 diluted that I then diluted to 25/75 (thinking I was using undiluted 6 weeks ago during flush).

A 25/75 mix of antifreeze and water has a freezing point of 10ºF, however unless the entire cooling system was drained dry then this merged with however much 50/50 mix was still in there. The freezing point would be somewhere between 10º and -34º.

2. The system was no longer full (probably 85%) which means that the small intake leak over the last 6 weeks had further weakened my anti-freeze protection.

The anti-freeze protection is determined by the antifreeze-to-water ratio, and is not affected by the amount of coolant in the system. A leak can’t weaken it.

Does the burb have freeze plugs in the block? If so how can I tell if they "popped"

Every automotive engine I’ve ever seen has freeze plugs. If they pop you have a HUGE coolant leak.

I did drive 50 miles in -4 degree weather and the only thing I noticed was while my front heat worked great, the rear was blowing cool no matter the setting.

I would suspect either a sizable air pocket or a failure of a heater control (hot water valve, air blend door, etc.). If you’re not experiencing any other symptoms, it’s likely you lucked out. You’ve pretty much tested it by driving it.

Thanks Gary… I see you are in KCMO so you know the weather we are dealing with. :smiley:

I am relatively certain that my protection stopped at 10F because I did drain it completely and the mix was 25/75. I will check tonight when I get home to make sure.

Good to hear that I may have lucked out. I thought maybe the rear heater core was still frozen since it remains parked outside (way too many cars and not enough garage space).

I am going to leave the rear heat alone until we thaw out but 75 miles so far and temp never went over 1/3… so far so good :wink:

Excessive engine heat is what jacks up your engine. Coolant/antifreeze systems manage excess heat. Unless your temp guage told you otherwise, it doesn’t sound like you ever overheated the engine so big damage is unlikely. Now, depending on where the coolant WENT, you might have other issues. I’ve not heard of low water levels damaging a pump or anything else, for that matter, but you never know. Your heating system is basically a mini radiator circuit that pulls some coolant into the cabin, runs it through a cute little radiator and sends it back to the engine to get warmed back up. Depending on how the whole thing is put together, that heater circuit could be a bubble just waiting to happen. So don’t fret too much about a bunch of coolant being ‘gone’ because it may have just filled the heater when the thermostat opened. Or something.

Also, swapping coolant isn’t always as simple as doing the oil (remove plug, drain juice, replace plug, add new juice). Some systems need to be burped, and that process can be simple or a relative PITA (old Toyota MR2).
ETA: Hm, hadn’t thought about freezing damage to the heater cores. That’d be a steaming mugful of suck.

Unless there’s a huge differential between the freeze protection level and the outside temperature, it’ll take a really long time for your coolant to freeze thoroughly enough to crack the block or pop the freeze plugs. That’s why people who live places where it does occasionally get below -34F can usually still get away with running 50/50 blends because even if it (say) gets down to -40 it’ll still take days to actually freeze solid. It’s only the poor bastards who live places like Fairbanks where you can get stretches of multiple days of those temperatures or temperatures WAY lower that have to do 70/30 mixtures.

So if your coolant was good down to 10 and it only got a bit below zero overnight, I doubt you broke anything.

The most common reason for a radiator to show low on coolant after a cooling system service is that whoever filled it did not patiently wait for the thermostat to open while running the vehicle. It can take some time to get it warm enough in cold weather. It is absolutely imperative to run the motor until hot coolant is circulating through the radiator and keep filling it until this happens.

If you have since drove it 50 miles and it didn’t do anything wonky I can’t see anything damaged. If you lost a freeze plug or cracked the block you might not be here to ask the quaestion, you’d be a popsicle waiting for the tow truck by now.:smiley:

As far as the back seat heat, from what I’ve noticed driving my 2004 Chevy is that this single digit temperature spell we’ve been is is affecting my cabin heat times. I drive 8 miles from home to my shop, usually in winter I can turn on my fan on high and get comfy heat at a certain intersection. In this cold spell it’s a lot further down the road before I get the same amount of happy heat. Sounds self evident when you say it out loud.

50/50 anti freeze is the standard here.
stronger mixes will slush up faster than 50-50.
Although we have seen only a handful of -30< F days there
Although i never buy pre-mixed anti freeze only because water is so darn much cheaper to get out of the tap.
One thing about antifreeze is it will slush up instead of freeze solid and expand thereby causing cracked blocks and sometimes just a pushed core plug.

As for the rear heater not working, i can think of 2 possibility’s.

  1. the weak coolant hasn’t been flushed through and you are still slushed up…
  2. in the process of running low and refilling you ave air in the rear heater core.

AND

I do not see a correlation to an audible intake leak and weakening your antifreeze. I have never heard a coolant leak but have heard vacuum leaks.