95 LT-1 overheats 110,000 mi, owned 8 months
The problem is solved !!!!! 8 AUG 08

Albert's suggestion of using K&W's fine nano particle sealant to seal the small head gasket leak worked.

You can read this thread and get many suggestions, the Corvette FSM is the basic guide.

Analysis: despite following the FSM and adding additional steps such as using block tester blue dye and CO sniffer, the head gasket leak could not be confirmed. No water in oil - no oil in water. no spark plug fouling.

The FSM says to add sealant pellets to the coolant; however, it seems this leak was too small to be blocked by the sealant particles. But, continued to compress exhaust gas into the cooling system. After 10-20 minutes at road speed, the hot vapor pockets were formed, overheating and coolant puking occurred.

The cooling system would hold 17 psi pressure for over 1 hour. But, the cooling system would NOT hold a 27 psi vacuum... dropped 2 psi in 30 seconds. ??? very small vacuum leak via head gasket ????

The fine nano particle sealant did fill the exhaust leak passages.

Thanks to all that helped...Albert should get the C-4 golden award

Joe



May 4
1. Started over heating 4 weeks ago REAL overheat digital over 255 and puking and steam into plastic over flow at shutdown
1a. cleaned radiator and a/c with compressed air, found plastic bag, high temps continued
2.Tested thermostat OK but replaced
3.Tested temp sensor OK, but replaced
3a. water pumps replaced past year, 6-10,000 mile
4. No leaks and holds pressure, new pressure cap
5.fans come on at 225 and 238 as per manual
6.Fans continuous with A/C as per manual
7.Flushed system and refilled with vacuum adaptor, 50/50 fluid
8.IR temp drop across radiator at all temps 180-240 ranges
9.Checked with blue dye block tester 4 times, no exhaust in cooling system
10.Temps swing thru 200-240 gradually building, then after 4-6 miles over 255 and A/C shuts down
11. Does same with A/C off
12.Checked radiator air passages with plastic wire tie...no expanded tubes or blocked air
13.No change in symptoms: temps up and down but gradually build, after 4-6 miles 255+, puking
14. Replaced radiator OEM, vacuum refill
15. Same symptoms; temps up and down, but gradually build, wait in traffic temp builds to 255-260
16. added manual switch to fans for testing, fans come on normal, but I can activate at lower temps while driving.
17. Same symptoms, I turn on high fans while driving at lower temp 220 rather than 238. still goes to 255+....but delayed some
17a.Oil temp is slightly elevated when coolant high, but never past middle range
18.Experienced car guys and technicians are stumped over these 4 weeks, understand LT-1 run higher temp, it is actual high temp 255+ A/C shuts down, pukes and steams into the plastic overflow when stopped.

Any ideas??? thanks all Joe

ADDITIONAL as of JUNE 22
Sorry a bit slow following up...I was in Europe and Russia longer than expected:

1. Put in new OEM water pump (old one seemed OK)
2. Loosened the vapor tube on the back of port (left) head, blew 15# of compressed air into the front metal tube, air passed easily at back of heads... vapor tube not plugged
3. Did the block test with the blue dye again OK
4. Runs very good
5. Let idle for 20 minutes to check out everything. Fans cycled properly
6. Turned fans on manually for street test drive.
7. Drove around neighborhood streets for 15 minutes... temp up to 220
8. Under load at highway speeds, it slowly raising temps @255 F the A/C shuts off (as programmed)
9. Temp went to 270 before I could return to garage, oil temp below mid gauge

The good ideas you all were kind enough to suggest, have not helped

Any other ideas ? Thanks much. It is now an obsession to solve this cooling problem.

ADDITIONAL as of July 30
1.I pressured the cooling system to 17 psi...it held the pressure for an hour. even rotated the engine a few times to be sure had open valves on a cylinder if HG is the problem.

2.I drained a couple of gallons of coolant from system and used used a good vacuum coolant fill unit (sold by snap-on). I pulled a 27 inch vacuum on the system...had a slow leak down dropped from 27 inches to 25 inch vacuum in 30 secs. Leaking via head gasket ???????

Filled the system with coolant while under vacuum as per device instructions. When system was full still had about 5 inches of vacuum.

3.Ran the car in the driveway for an hour with 95 F ambient temps. Fans cycled properly 228 on/217 off. The drove the car on the street up to 40 mph for about 15-20 minutes started same old heating problem. By time I returned to garage, it was up to 250 F on the rear analog guage and 220 on front digital guage. steaming and puking into overflow.

Joe

 

According to the manual you seem to have done nearly everything but have you checked the ignition timing? Also check belt tension. Do you not have to burp the system to remove air pockets ?

 

My initial reaction was head gaskets but you seem to eliminate that with the chemical test but did you check for a stuck T-stat?

I saw that you have a recent water pump but is it still moving water? IE did it seize or break the coupling?

 

Ray, thanks the timing may be an issue...have no codes but that is another check item. These C-4s with the surge tank on the firewall and the the bleed screw at the thermostat are to not require burbing. However, that is why i refilled the fluid twice with a vaccum fill adaptor... pulls vacuum as fluid is added.

Belt tension, these LT-1s have direct drive on water pump, no water pump pulley.

Joe

 

Thanks, #2 tested T-stat, ran afew days without T-stat, put in new 180 as specified.

With that fire wall surge tank, difficult to visually verify that fluid is moving. Temp drop across radiator would indicate flow. Don't mind a $140 pump, but do not like to throw parts. Was wanting feedback if these direct drive pumps do stop?
Thanks Joe

 

You do have to bleed the air out with the t/stat open or it will overheat due to trapped air. Did you do that?

Since there is constant flow thru the heater hoses are they both hot? If so your water pump is pumping.

 

Is the car an auto or manual? I have a theory sometimes that on automatic cars, there is a trans problem and the trans cooler in the radiator is what is causing the overheating. Doesn't seem likely, but I thought I would throw that out there.

 

Yes, Andy bled the air out via the brass screw vent at the water pump. And, also used a vacuum fil adapyor which pulls vacuum as you refill fluid

Thanks JOE

 

Thanks Bruce, that tranny cooler theory crossed my mind as well. The temp spike does seem to be more detectable when accelerating (work load on tranny). The tranny temp read out is not high, but I have not checked it at power or work load.

Joe

 

Here is one from the old days, check to see if the spring in the lower rad hose has collapsed causing it to suck closed blocking flow. Timing on the LT1 is not adjustable so doubt that could be an issue. Good luck.

 

LT1s have steam vent tubes at the rear of the heads (there's a cross-over pipe from the left to the right and then it runs along the top of the passenger side cylinder head between the head and the intake). I'd check to make sure that the tubes aren't crushed or clogged by blowing some compressed air into the tube (at a very low psi) that runs along the intake.

Might also want to verify the heater core isn't clogged, causing a restriction of some sort. Pull the heater hoses off and tee them together for a quick test.

 

What was the last work done to the car prior to any over heating problems? Possibly any snags left over from the last operation? It sounds like you've covered everything, but obviously, you haven't.

RACE ON!!!

 

Thanks, I saw that steam vent cross-over in the manual, but could not locate that on the engine. I thought the plastic bag and trash high temp may have caused the some internal scale to dislodge and clog that steam vent cross-over, but could not find it. Heater core is a good check. Thanks Joe

 

Pump was replaced before I bought it (year 6,000 mi).I ran it 8 months with no problems. But, last thing repaired is always good approach.

Thanks JOE

 

Where does that vent tube terminate or tie as it comes forward from rear cross over from two heads? Probably simple but I did not see it.
Thanks JOE

 

It runs under the passenger side fuel rail cover and flows thru the heat exchanger under the throttle body.

 

Sure sounds like a bad/non working pump to me. You pretty much covered everything else.The amount of time it takes to overheat is pretty consistant with no flow condition.

 

If you decide to change your water pump you should consider going to an EWP, Meziere HD. That way you can flush the system easier.

 

Thermostats open by a wax pellet expanding. Once a thermostat overheats, some of the wax gets pushed out under overpressure inside the thermostat itself. After that happens, the thermostat will not open as far as it should.

At first I was going to post it sounds more like a cracked head or bad head gasket but you've ruled that out. Your radiator cap should be no more then a 15lb cap at most. So the first thing to relieve pressure would be the cap instead of a hose. Right now you would be wise to check the heater core. They usually can't take much over-pressure.

 

Ryan, many thanks for suggestions:
I ran with old T-stat after testing OK, no T-stat, and new T-stat...symptoms the same.

The new cap was a 16#, good idea to use old stock 15# . I will by-pass heater and check that angle...makes sense.

Joe