Need advice on 95 overheated today. Finally got the heater core in a couple weeks ago and finished the carpet replacement. Took the car out last week for about an hour ran great heat/ac worked great, engine ran great with the supercharger. Drove about two hours today heat on at 78 runnin down the highway I floored it from 75 to about 135 , then the bad happened heat turned cold then check guages lights up and the temp is at 255 so I coast to the ramp and shut it off. Radiator cap let's some coolant out all over the one side of the engine. Radiator is gurgling, top hose is swelling and I can't touch it. The lower hose it hot but more touchable than the upper, the one heater hose it hot as hell, but the other less hot. I let it get down to 200 and drove it to my garage where it escalated to 265 rapidly. The fans are on only when the car is running, changed new thermostat when I put in the heater core weeks ago, new coolant, newRadiator, no coolant in the oil, no white exhaust. What could be going on , thermostat? Water pump was changed 5000 miles ago when the msd distributor was installed. How can it work so good then just by going fast it overheats that drastically. How can I tell if the pump is working. I'm going out to look at it in the morning. I'm just so through with this car,I thought I was finally done with the new interior, then this. I'm leaning towards a bad thermostat and definitely changing cap. Anyway to tell if the pump is pumping like you can on an older car where you could see the water moving in the radiator unlike on this model. Any advise before I start changing parts.

 

I would check the thermostat first, then confirm the water pump is functioning, unfortunately nowadays, even new, Chinese made junk, is no guarantee it will last. If those two are good to go check your radiator to confirm its not plugged up.

 

...

 

In addition to making sure the thermostat is working correctly, also make sure the correct part is actually in there. There are tStats that will bolt in and seal up but don’t have the extension on the water pump side.

The thermostat should look like this with that extra extension.

 

Went and changed the thermostat after draining some coolant, go to start it and immediately coolant blowing out of the tank. Car won't accelerate then the dreaded white exhaust, must have blown the gaskets or cracked a head so now I'm going to start tearing it down to see what carnage it has. After getting the car home it started up after cooling down so I figured it was a stuck thermostat. Oh well, I'll have way to much money in this car by the time I'm finished. I'll have them bury me in it like the movie Used Cars.

 

You have a supercharger I see. Do you have a boost gauge and if so, what’s the upper level boost psi? Also, do you have a wideband A/F setup and if so, what’s the A/F ratio when under the max boost?

The LT1 is a high compression engine to begin with. Start adding boost and fuel delivery gets really critical. If it goes lean under boost then cylinder pressures will skyrocket. Then, bad things happen

 

Just some more thought after reading your initial post again. You said during a full throttle blast she blew coolant out of the radiator cap.

This is not uncommon on a boosted engine that goes lean under boost. It can be a single bad injector going lean in one cylinder or lean across the board affecting all cylinders.

Among several possibilities is head gasket breach caused by excessive cylinder pressure. When the combustion chamber pressure breaches the head gasket, the water jacket gets subjected to the combustion pressure and the radiator cap gives way since they’re designed to release at 19lbs or whatever the cap rating is. The coolant then blows out through the caps normal release function.

If this is the case, it will continue to be a problem until you address the fuel delivery situation.

 

The engine was built for a supercharger, worked great for 5000 miles in 5 years. It's set for 6lbs boost, I have a boost guage, afr guage, new everything, msd with rev limiter, boost retard. Something just let go and I will start taking the engine apart in a week or so. I'm hoping for a head gasket problem, and praying for the engine block to be good. No water in the oil so far. I'll pull pugs when I can first, maybe a compression check. Too much going on at that speed to look at all the guages especially when temp climbed from 200 tp 260 in a couple seconds. I did see water blowing past the cap, 16 lb also new. When I pulled to the side of the road, it restarted fine and I drove it about a mile or so to my garage, it did it again, I came back in the morning and that's when I restarted it after topping off the coolant, then white smoke and chugging. Thanks for the replies and help, I'll keep you posted on my findings. If I get it sorted out I'll probably be done with the car, sell it at a loss, and go chase women and start drinking again, 😄

 

I have a supercharged 92 Mustang. Vortec V3 sci. 10 psi. I was puking coolant under boost because of one bad injector. It didn’t really show on the wideband because ECU was compensating for the lean condition under normal driving I suppose. It would hold up to about 5psi. Higher up it would puke out the cap.

I’ve since put bigger injectors in but I’m running it na now. I still have to re-tune for the new injectors before I put the blower belt back on.

Point is, sometimes even monitoring the A/F isn’t enough to save you. Things happen really fast under those extra conditions. The 95 LT1 has knock sensors that should play a role in retarding timing if they sense knocking from detonation caused by lean conditions. But again, things happen so fast that the knock sensors can’t always save you.

Anyway, it’s possible a lean condition could have led to initial rapid coolant loss. After that breach and whatever damages it may have caused, the engine can’t manage the coolant even under normal conditions.

If you do head gaskets, check the not only the head for flatness but also the block deck. Anything out of spec should be machined. For reliability in boosted engines, you need everything to be perfect.

 

If it’s head gaskets you’re doing, here’s my recommendation. You can also special order these in different thicknesses. If you do any machining of head or block deck, compensating for removal of machined surfaces by using thicker gaskets can be a good move. The LT1 compression is already high. You don’t want to push it higher by milling, especially in a boosted application.

https://www.cometic.com/products/C5646-030