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Cooling problems

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
My 96 LT4 heats up slowly , and will sometimes even maintain regular operating temp. between 195-215, but the second it gets to 225 it skyrockets up to 245-250 and completely fills the overflow tank to bubbling over. It does this whether I'm driving or if its started cold and allowed to idle in my driveway, makes no difference. Any ideas? I've replaced both the thermostat (180 deg) and the radiator cap (16 lbs) with no change in condition.
 

fixvet

Well-known member
Joined
Apr 4, 2002
Messages
139
Location
Clever, MO
Corvette
1998 Two Tone Torch Red& Black Coupe
Trance:
Have you checked to see if your cooling fan(s) are operating correctly, with and without the a/c being on??
Fix
 
V

vetsvette

Guest
First thing I would do is clean the radiator. A lot of stuff collects between it and the A/C condensor. Next flush you system completely and put in new Dexcool and distilled water as per the owners manual. When you replaced the Tstat are you sure it was made for the LT1/4? These engines require a two way Tstat. If all this stuff is good, I give up!
:confused
I'm running a 160 Tstat w/Hypertech programming on mine and I seldom see it go over 185 even in the middle of the summer.
Good Luck:upthumbs
 

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
I have a hypertech programmer with a hypertech 180 tstat, the cooling fans come on around 195, and the radiator is new. I'm thinking its the water pump.
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Ouch,

You could have a blown head gasket. The water pump on the LT-1/4 is a direct drive off the camshaft gear. If you fans are coming on, thermostat opening, and cap is good, you should maintain a constant temp. Since the water pump is a direct drive, it should be turning the impellar which would be moving the coolant.

Now, you could have a clogged radiator as mentioned here. That is, you may have picked up some crud that is trapped between the a/c condensor and the radiator. This will kill the radiator efficiency.

Otherwise, open the cap and look in the pressure tank while the engine is running (from a cold start). If you see air bubbles in there coming at a fairly stream, you may have a blown head gasket.
 

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
The car is running fine.....all 310+ rear wheel ponies are running strong. I tested the car this morning, from a cold start. It took 10 minutes to warm up from 45 deg to 180 deg. It kept going until 194, and held there for another 10 minutes, so I took it for a drive. 2 miles down the road, at a medium pace, and it never got above 200. I turned around, and ran it hard on the way back. It got up to 205, I let off it, and it cooled back into the 190s, I got on it again, this time it went to 215, and rapidly went to 235 (about the time I was pulling in the driveway) and then crept up to 240 when I shut it off. I popped the hood, and the overflow tank (that was sitting dead-on the "cold" mark that morning) was bubbling over with coolant and making a big green puddle under my car. This is the oddest cooling problem I've ever had with a car.

I felt the upper radiator hose after the car was warmed up. It was warm, and when I squeezed it, I could feel coolant flowing through. I felt the lower radiator hose, it was cold.
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
I am stumped, unless the thermostat is bad and not opening on the bottom side. It is a very unique model with a twin spring seal mechanism.

Keep us posted.

One other thought I had, but I am most likely wrong. Maybe the cooling fans are wearing out and not pulling enough cfm to keep it cool all the time.
 
V

vetsvette

Guest
I don't see the fans going bad on a fairly new car like yours. Did you say GREEN puddle under your car? You should be running Dexcool. It should be orange. Don't know if that would make a difference tho.:confused
 

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
Yeah, the cooing fans seem to be working great, cause I can feel the cold air making ME cold when I'm standing over the engine.

What is this dexcool stuff people are talking about? Why is it different from regular anti-freeze? I know they can't be mixed, but is one really better than the other?

I'm thinking more and more its a head gasket problem, cause it seems only when I rev it higher in driving that the heat really starts climbing, so I'm guessing more heat than normal is escaping into the cooling system. Is there a definate check for this? Like, isn't there some device that you plug into the radiator cap area, and it changes color if you have a blown head gasket?
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
The headgasket could be the problem. The trick is seeing air bubbles like I was saying earlier. You can tell this by starting the engine cold with the cap off. Watching the pressure tank. Look for bubbles to be coming out of it as the car heats up. This is a sure sign of trouble.

You need to inspect the upper and lower radiator hose as well and make sure that neither one is collapsing under hard throttle.
 

Paul G

Well-known member
Joined
Aug 27, 2001
Messages
200
Location
Griffith, IN, USA
Corvette
96 CE LT4 Convertible
I felt the upper radiator hose after the car was warmed up. It was warm, and when I squeezed it, I could feel coolant flowing through. I felt the lower radiator hose, it was cold.

This all by itself would mean the t-stat is not opening. The lower hose should be warm if coolant is flowing. Try taking the stat out completely and see what happens. The car will run cold without the stat but that wont hurt anything for testing purposes.

This may sound like a stupid question, but is the stat installed the correct way? Spring points down toward the engine.
 

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
Yeah, I know there are some real ......lets say "uneduacted" people out there who happen by blind luck get themselves the keys to a vette, but no......the t-stat is installed correctly. I have two of them, the stock 195, and the 180 I replaced it with. ITs overheated with both of em in, but I will be removing it tommorow, and check to see how things work. I hope the rubber "gasket" off the t-stat works by itself, cause simply removing the tstat allows coolant to slip out.
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
I don't think you can run the LT1 without a thermostat.

Man, I have been pondering your problem off and on since I first read about it. I have done a couple of LT1 transplants into other car (36 Ford, two 1500 chevy trucks, etc), and always had initial problems with them overheating until I could get all the air out.

Did your overheating start after changing the first t-stat?

There is a bleeder valve on the upper intake hose to purge air.

Have you opened it and let the air bleed off?

If you have a large air bubble trapped in the engine it will do what you have said as well because it will steam the air in there and force it to race out the overflow tank and puke fluid as the air expands. It will also give you false hot signals as the radiator will feel cool, but the gauge on the dash will show the engine off the chart.

If I am on track here, go back and follow the whole procedure for purging the air and I think you may have this problem solved. The flip side of this is that sometimes you can pop the head gasket by running the car without the system purged of all the air. So a simple thing can turn into a complex thing if not dealt with right away.

Check it out and let us know.
 

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
Yeah, I bled the air out each time I opened up the system. I ran it without the t-stat this morning around town before I took it to my mechanic down the street. No change in condition, and both upper and lower hoses were hot, and under pressure when I squeezed them. So, he's gonna check everything out, do a block check, ect.......and we will know today.
 

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
Well, the final result wasn't the worst, but it wasn't the best. The head gasket was blown. The heads were slightly warped, but nothing that a little milling isn't going to fix (I think it was like .005 or something ? ....I'll double check).

Head change gasket sets for LT4s are hard to come by, but we found a dealer in Texas that has them, they'll be here tommorow. The Machine shop is doing the milling, and a valve job. The car went in on monday morning, should be back Wednesday afternoon, thursday morning at the latest.

The job is supposed to cost $1400 all told......pretty expensive for overheating, but highperformance=high maintainance
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Sometimes I hate it when I am right, because it was the worst case scenario.

Glad you found the problem.

Do you think that the gasket blew from not purging the system right after changing the first thermostat? In other words, there may be another problem there that could cause it to overheat again.
 

Trance_LT4

Well-known member
Joined
Dec 11, 2001
Messages
140
Location
Suffolk, VA
Corvette
Red 96 LT4 coupe
Nah, the overheating problem was before the gasket change. I'm certain the warping and the blown gasket was from overheating (which was caused by a broken temp guage, and me not seeing it overheat till the "check guages/check engine" light came on)

I'm just glad its not the same problem I had with a pontiac I once owned. The block cracked and leaked coolant all over
 
V

vetsvette

Guest
Are you going to get the heads ported and maybe a three angle valve job while you are at it? Might as well since the hard part of that job is removing and re-installing the heads. You are already there.
:w
 

maxrevs85

Well-known member
Joined
Dec 17, 2001
Messages
709
Location
Eaton Rapids, Mich
Corvette
!985 ,blue coupe, 4+3 Z51
Cooling problems?

Although Ive had no cooling probs ,because I only drove the car 4 times and all was in cool weather, I decided to pull the radiator . Mostly since I'm doing engine mods and it was time to consider this aspect. Annnyways.....when I removerd the rad, I found 4'' of leaves and debrie(sp) between the the rad and condenser at the bottom. When I looked at the front of the radiator it looked like a furnace filter after a heating season. The condenser was just as bad. So maybe before we go to far with what we think is a cooling problem , you might want to consider taking a look .Remove the air filter duct and pull the top radiator cover.

Just some food for thought........I think its a coooooolllll idea :cool
 
7

78SilvAnniv

Guest
More ignorance on the way...

...I thought a blown head gasket meant you'd have oil in your radiator water?
I thought it was sort of strange to advise looking for air bubbles.
Will someone please explain?
Silver
 

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