OK well my previous roll around i thought i had my overheating fixed.
1996 LT1 Automatic.

Now im wondering if maybe theres more too it.
Just after the coolant flush and for about 2 weeks... morning temps have me running on hiyways around 194-196 in cold weather..
Highest temp i had seen even was around 203 (other than sitting in traffic) once your moving it dropped back down FAST...

All of a sudden this afternoon, about 60 degrees i stop to get gas... leave it running ... (normal so far even in traffic i havent seem more than 204).

I get back in car .. look down at the gauges and notice 248!... WTH Im getting on hiway, maybe its jsut no air... about 1/4 mile .. its slowly rising ... I take the next ramp and pull over with full intentions to shutting down .. ...

As i get off the ramp .. i notice the low coolant flicker a few times ... and the temps plumet down to 205... odd so i stop and watch for a bit ... all seems welll ... So i drive off slowly ... this time im staying on no traffic back roads...

Very similar happens again about 5 mins later ... im almost home .. temps drop back down to 208 ...


Havent noticed any leaking coolant as of yet .. i guess pressure testing the system will be in order ... and checking the plugs will be in order next.

... Any know the ibest way to actually check and see if a waterpump is working 100%?

Other things .. i pulled out the thermo... wanted to see if it maybe was gummed up and see what things looked like around it ... Looks to be in good shape ... and its 180 degrees ...


Im up for suggestions to make my saterday ... greasy

 

gee... you need the combustion test kit. There is a test that can be run on the coolant, to determine if there is combustion by-products in the coolant. This would tell you if a head gasket is bad.

Get that test kit.

And you won't get greasy.

It also sounds like there may be a problem with the fans... do you have a helms manual? if not, get one.

 

nah fans came on just fine ...


acted almost like the thermostat stuck...

 

My vette is the only car I have ever owned that devours a thermostat annually! They stick partially closed. Don't understand! It's just a thermostat!

Not sure what year you have, but air in the system can cause the low coolant light and a similar heat problem

To get the air out, I crack the hose clamp at the thermo housing when engine is hot and wait till I get a solid flow of coolant

seeya

 

Have you checked in front of the radiator for debis I found a large piece of newspaper on my 89 before I must have picked up going down the road! My air flow was half pluged

 

okies im up for more suggestions.
This is what i have so far.



1. made sure radiator was clean (outside)...
No problems... in fact most of the time the radiator seem fine.

However i am concerned that a 180 thermo was running around 200 in 40 degree weather.

2. Topped off the radiator ... over the next 24 hours i would crank the car let it get to about 200 while watching the reserver and topping it off.
Then cap the radiator ... run a couple miles to build some pressure ... and crack the bleed off screew thats right on top of the thermo housing ( i presume thats what it is).


Sunday morning i decided it was time to test it out...
Wife and I took it about 20 miles maybe a bit more. Country road so hiway ...
Zero problems..... I thought i was good to go.


On the way to work this morning it was fine ... until i started getting in stop and go traffic ... at that point i noticed the temps rising again. I turn on the heater wide open to help out (and open a window)

Its blowing cold air... both coolaing fans seem to have kicked on ... temps hold around 255 im starting to get worried again ... traffic opens up a bit ... so i ease foward .. around 2000 RPMS i immediately istart feeling hot air ... and temps drop to 205ish...

I stop in traffic and temps start going up ... air goes cold again.


Im kinda lost ... As its been 10 years since i really done much car work ... IM seriously thinking of buying a replacement waterpump and thermo and replacing both..

I guess it will all start coming back as i work around things.

In addition i pull plug #7 ... it looks fine ...
I also noticed what looks like a 1way valve inline right under the reserve tank.... almost looks after market .. that normal?

Thanks again for all the help so far

 

If you're seeing temps. in the 248 range, something is most definitely wrong. You can have a thermostat that works intermittently. One of the first changes I'd do is put in a new 180. Don't put in a piece of crap thermostat. Get a stant or an oem. Summitt Racing sells many different type of thermostats and matching gaskets.

As stated, check your radiator and condensor. Ensure that nothing has blocked the flow of air. Make sure you don't have air in your system and that you have enough coolant in your system.

Your temperatures are getting mighty close to the oh sh_t stage.

 

You running Dexcool

 

LOL anything over 140 im already starting to worry.

As far as coolant ... *D&FDFHH#$ is there a GOOD way to get it topped off? I mean seriously i spent hours trying to make sure it was full ... and twice now i thought it was.... But kinda concerned that im not and thats part of the problem.


As far as a intermitant thermostat ... STUCK closed could cause the overheating ... but what about during that same time getting nothing but cold air in the vents?

ohh and no dexcool ... it was already converted when i got it.

Dunno yet if i want to convert it back ... other 2 im running have it ... be nice to have all 3 on the same bottle

 

A 180 running 200 in 40 degree weather is right.
The temps will run +20 degrees 180=200. In cold weather it just takes longer for the car to reach operating temps.

Did you test the thermostat? Its filled with wax and at 180 degrees the wax melts and the thermo opens.

I wouldv'e replaced it, but to test it put in a pan and heat the water to the point where it opens then check the water temps.

180 degrees fully opened.
Take the cap off of the radiator (cold engine) and run the car look for the water pump swirl in the coolant to see if the pump has good pressure. Is the pressure cap holding the right pressure? While the cap is off look for bubbles.

You don't have to drive the car to get it up to operating temps it will do that in the driveway. Check the time it takes to get up to hot and watch the fans. Also see if turning on the air cond brings down the temps.

 

Not sure why people are talking about changing thermostats and such when he says:

If you worked on it before this started then maybe you have an air bubble.

Otherwise you have a leak, internal or external. Find the leak and fix it.

 

well the low coolant flickers when the temps go from 260 to 200 in about 3 minutes.

It doesnt stay on it just flashes a second or 2...

I havent found a leak yet ... only time it seems to lose coolant is once i get to the point of overheating.. As far as topping off the coolant, ive tried and tried to get it topped off, each time i thought i done good. ... Anyone have a fool proof way?

 

Your description of what you did sounds fine, and I haven't found the LT1 to be hard to bleed. Which unfortunately indicates a leak.

 

IF it was running at normal operating temp, and blowing cold air out of the heater, I would think the heater core is clogged.

When you had the coolant flushed what did it look like??

Im not sure how the LT-1s are set up but can you disconnect the heater core inlet and outlet at the firewall and blow air or water through it??

A friend of mine had the same problem with another vehicle and he had to blow out the heater core twice and at first he could not blow air through it, but then chunks came out and it was fine.

Take a look into that.

 

as far as the leak ... i havent found one yet ..

I've checked it hot and cold .. both with the radiator cap on and off.

Ive even let it run til it built up pressure .. then let it sit ... it had pressure like 45- to an hour later.

cant find any leaks .. not even a damp spot
Bad luck with air bubbles ... or hardware.
At this point i think ill just have me a pump and stat deliveried this weekend, and replace the radiator cap while im at it.

Ill take that same time to do a complete flush of the system and see what i can do from there.

1st vette or LT1 pump ive replaced


Oh and the vents blowing cold air .. they work fine normally.

Just seem to act up at the same time the car is trying to make me have a heart attack with the heat ..
is it possible the impeller is slipping on the shaft ... or is the LT1 lots diffrent from some of the older ones i tinkered with?

 

As far as any tricks to filling/topping off the surge tank, I don't know of any. The service manual describes it this way.

With the engine cold, open/remove the surge tank cap. Top off with coolant. Tuck a few wrags around the bleed screws and open them. There should be two one on the thermostat housing and the other at the throttle body inlet. Open them until you have a good flow of fluid no air. Close and re-top off.

Start the engine and let it idle and warm up. Monitor the fluid in the surge tank by observing it with the cap off, and monitor the coolant temp. When it gets close to 180, the thermostat will open and you will see the water start to flow now through the surge tank spout. It may drop down just a hair, just re-top it off. The engine should stabilize about 190's and the coolant should have good flow to it and remain just below the filler neck.

Go ahead and put the cap back on and shut the engine down.

The next morning after the engine is completely cool, open the cap on the surge tank and verify the level is at the base. It should be. If it is not, then you have a leak somewhere.

Also don't forget about the heater core. It is part of the coolant system. If it has any small leak, it may never show up as a dampness on the passenger side, but will certain induce air into the system, as well as account for some loss of coolant. When I replaced mine a month or so ago, I noticed the temps were a few degrees better on normal cruise and sitting in traffic (highs were lower).

Also, there are two areas of the radiator you want to inspect and clean. Sounds like you found the obvious one which is under the nose in the mouth. But also look between them. If you position yourself on the passenger side there is a small opening in the radiator housing case that you can shine a flashlight and look inbetween. Inspect for debris. If you find some, I found a ton of grass on mine, you can fabricate with a piece of pvc pipe and attach it to your vacuum cleaner hose and very gently slide it in the hole in the case and carefully suck off all the junk. I cut the end of the pvc at a 45 degree angle. Otherwise you'll have to pull them and get the case off to clean between the two.





Here are two pictures of the area I'm talking about.

Hope this helps.

 

My Mercedes blew cold air in the heator the coolant was too low.

 

...i had the same problems in my 94, but i gave up trying to figure if it was this or that......so i just installed an aluminum radiator, went 400 miles saturday....the temps went to 200 deg and stayed there did not matter if i was in traffic or not....i am very satisfied that i did the right thing......

 

found some REALLY odd results this morning


driving normally at 70MPH ... constant 200 degrees (about 18-2000 RPMS
pull it down into 3rd gear

and the RPMS jump to about 3k.
TEMPS start dropping and hold at around 194.

back to overdrive ... and temps slow climb back to 200 steady.


/shrug new waterpump and thermo are on the way just in case from GM parts direct...

What the heck ... replacing them 1st .. next will be a radiator from Dewitts

 

It will suck to replace all that and then find out it is a headgasket.

Diagnose the problem don't just throw parts at it.