Coolant level always low in overflow tank

[Blaze One]

1995 CPI 4.3 engine.

I noticed my coolant level in the overflow tank was about 2" below the "full hot" mark .

I added some coolant up to the line .

Drove 80kms , and not the coolant is back down to where it was before i topped it up .

Also , the temp gauge in dash would get close to the red when stopped at a light , but go back to normal range when I drove .

The temp gauge never did this before i topped up the coolant level .

There are no leaks coming from the engine , and no coolant in the oil etc .

The radiator and t stat and hoses where all replace 2yrs ago .
along with the intake gasket.

Any ideas as to why my coolant is disappearing to this level ?

[HenryJ]

Sounds like you do not yet have the air purged from the system.

Intake gaskets. Time to change them again I suspect. Do a system pressure check. A good radiator shop will have the tool. If it is not leaking externally, it is leaking internally.

[RebelKid1822]

just an idea, but when you stop at a light it gets hot, that is when the waterpump is spinning its slowest, and when you speed up agian the temp goes back to normal, that may be because the water pump is then spining faster. so it may be a bad water pump. purging the air out would be a great idea to try first. remove the thermostat, and make sure the block is completely full of coolant, then reinstall and fill the rest of the system. run it a few times-making sure the thermostat opens, and check the level agian. another tip. when the engine is running, look it the resivoir bottle and see if it bubbling. if it is you have either a craked head or blow head gasket.

[HenryJ]

Lift the lever on the cap or loosen it slightly. Squeeze the upper hose to purge air back to the expansion tank. Repeat until air is purged.
Run to operating temperature and let cool down. Fill again as needed to fill to the full hot mark when the engine is cold.

[Blaze One]

well today on my way home , the check engine light came on . the temp gauge was doing the same thing : cool upon acceleration , hot at a stop :

Pulled into my drive way , only to see a puddle of coolant under my truck .

Turns out that one of the hoses to to heater box on the firewall has a small hole in it . The coolant leaks down the fire wall onto the exhaust and evaporates quickly . That is why I never saw and leaks before today .
However the hole in the hose is now large enough to leak more and be noticeable .

I believe the CEL came on because there is coolant leaking on the distributor / plug wires . causing a rough idle ... sound plausible ???

I think once i get the hose replaced , and purge the air that was let into the system , it should be good to go .

That solves the missing coolant issue ... But do you still think my waterpump is bad ??

PS/ ... there were no bubbles in the coolant tank when the engine is running , so i assume my gaskets are still good. they were replace 2 yrs ago .

[HenryJ]

Sounds like you found the problem. I guess you could smell it burning? Fix that and see if it is cured. Let us know.

[Blaze One]

the leak in the hose was so small I could not see it at first . then today , it finally popped and the hole was large enough to let more coolant out and it didn't evaporate before it hit the drive way .

I let ya know how it works out.

[Blaze One]

so this is the mid section of the heater hose . the metal pipe connects two hoses , one attached to the firewall , the other to the engine .

But what is this orange/brownish stuff I found leaking out of the hose ??? ( this substance was present before the hose failure )

see pic .

[HenryJ]

Yikes! Dex crud! You have some serious flushing and cleaning to do.

[Blaze One]

Crap !

I was hoping that was not dexcrud .

The radiatior was replace 2 yrs ago , so atleast it is not old dexcool .

I will change it out for sure .

[Blaze One]

I replaced the hoses .
It seems i didn't have dexcool in the system , that must have been a old leak that caused the brownish/orange build up you see in the pics .

However ... my temp gauge is still reading very hot , almost to the red line .

The upper rad hose is COLD . even when the temp gauge reads hot .

The lower rad hose is warm/hot ( normal )

Could this be a faulty TSTAT ?

I drove the truck not more than 2 miles before the temp gauge was in the middle , seems it is reaching operating temp really fast .

Thanks for the help so far : )

[HenryJ]

Change the stat. They are cheap enough.

[roadrunner]

Many auto parts stores sell a "fail safe" T-stat. It is supposed to stay open in the event of a failure. I have used them with good success. At least your engine will just run cool and not overheat in the event of a failure.

[Blaze One]

I spent about 5 hours today trying to replace my tstat ....

there is a support bar/brace that goes from the belt tensioner to the waterpump . I could not get the the nut off the tensioner side of the brace , so i ended up taking the other end of the bar off the waterpump. I had to bend it out in order to be able to put a socket on the 2 10mm nuts on the tstat housing .

long story short ... everything is back together except i cannot get the support bar back on the water pump . i had to pry it off , so now it is never going to go back on .

I am not sure what to do now , maybe leave that support brace off ?

good news is , my tstat was stuck open , so at least my water pump could still be good .

fml

[F9K9]

I am having difficulty picturing your brace. Yours is a pre-'98 rig and a lot of changes were made between '97 and '98. Maybe a photo of your issue will help us in trying to walk you through this. With my throttle body spacer a t-stat swap is like 5 minutes or less. Without the spacer it might take 20 minutes tops.

[Blaze One]

Figured out how to reattach the brace bar . Truck is running good with the new failsafe 180 degree tstat . Runs around 160 when driving around town , tstat opens when it should when idleing in heat .

[F9K9]

You may throw a code with that Tstat in cooler weather. I always did until I relocated mine.

[green02crew]

I relocated my IAT sensor as well. I also have the 180* stat. I didn't throw codes but was worried I would once colder weather arrived. Haven't had an issue now in years since I did the mods. Runs cooler too for sure. Made the biggest difference when towing as it starts to cool sooner. Rare now that I get over 200* unless I'm running the a/c and sitting in traffic. Remember though I am pretty far North.

[Blaze One]

hmmm.... maybe i should consider relocating the iat thingy ...

thanks for the advice .

I assume there must be many diy on the topic .

[green02crew]

Wicked easy mod. Few minutes and you'll be done. The hardest part I had was what to fill the original hole from the sensor with! Well I used a K&N filter change indicator. Fit right in swell and lets me know when the vacuum is too much because the filter is plugged. At least that's the idea.

[Blaze One]

today the truck was running with the temp gauge around the 1/4 mark or slightly below when on the highway .

The outside air temp was 60 degree f .

I don't think getting the 180 tstat was a good idea , because i am running so cool now .

I have not had any CEL , but running that cool can't be good ....

I will have to wait a week before i can do the IAT mod .

I noticed that the upper rad hose is firmer now after driving the truck . Before the tstat change it was always COLD and squishy .

[HenryJ]

It takes about a week of cold weather to set the code for a stuck stat. I don't recall the number of failures required. Be patient, it will come if conditions are right.
Moving the IAT is enough to gain the time needed to pass the test.

[Blaze One]

considering i just changed the stat , I hope it is not faulty already .

The first day I installed the new tstat , i let it idle for 20mins and it reached 180 . today , it would not reach past the 1/4 mark on the gauge .

im baffled .

[HenryJ]

Sorry to confuse. The 180 stat will be seen as a stuck stat by the PCM. The PCM uses a set formula to determine how long it should take to reach the threshold value of 178. Readings from the outside air temperature sensor , ECT, IAT are included. Relocating the IAT buys the time needed to reach the threshold.

If you are building pressure, or getting air in the system, consider a test for hydrocarbons in the coolant. That would point to a head gasket failure.

[Blaze One]

I have noticed the odd bubble the overflow tank when the engine is running . maybe 1or2 small bubbles every 20seconds .

i will get the system checked out .

The upper rad hose is firm , but i am still able to squeez it a bit . Before i changed the tstat , it was really soft .

[HenryJ]

You should be able to pick up a hydrocarbon test kit. Bubbles forming in the coolant is a sign of a head gasket failure. Heating problems are another indicator.

[Blaze One]

Update:

I topped up the coolant in the tank and double check the rad to make sure it was full . squeezed the upper rad hose and burped out some air . started the engine and ran it untill it was warm , burped it gain and added some more coolant to rad and tank .

I then drove it for about 60 miles and didn't notice any coolant loss ( i did before ) .

So i think the missing coolant was not missing at all , I still must have had air int he system .

The air bubbles that would come into the overflow tank once in a while are gone .

There is no brown or oily fluid in the coolant , and I also drained my oil and checked it for coolant > Could not see any .

Now , I just have to replace the tstat AGAIN ! because I think i bought a faulty unit .

The first day after i changed the tstat it ran and warmed up great , second day , it won't warm up to even the 1/4 mark on the temp gauge .

[RebelKid1822]

if you bought the fail safe tstat and it faild, it would be stuck open and explain ur heat loss. as for the bubles, be sure they are gone. on all the chevys i have done head gaskets on none had coolant in the oil or vice versa. they had all blown right along the fire ring and were burning all of the coolant. i hope this is not a problem u have and that it is just a tstat.

[Blaze One]

I am changing the tstat tomorrow .

I have been driving for about 100miles and so far no coolant has disappeared .

[green02crew]

The temp gauge isn't exact either. Keep that in mind. I use a Scan Gauge to give readings and I get the exact temps that way. The stock gauge isn't too accurate in my opinion.

[Blaze One]

well it has been a few days and the new tstat is working great and my temps are normal . no coolant loss to be seen .

i guess it is on to the next issue . thanks !