402 ci s/c Vortec overheating

**BOSSONNOS** · 01-05-2007, 02:39 PM

I have also put this on the Vette forum so any help would be appreciated.

I have an LS2 402 stroker with an intercooled Vortec V& YSi supercharger, the engine is new and can idle all day with no problem but as soon as i run it up on the dyno at light throttle/cruise with no boost within 5 minutes it overheats.
I have replaced the radiator with a larger one, replaced the water pump, replaced the thermostat 3 times, blocked off around the outside of the radiator so air does not go around it but through it, removed the intercooler to check that it was not restricting air flow, set fans to come on early, fitted wire coils inside the radiator hoses to make sure they don't suck in, there is no detonation, afr's are perfect, checked that the head gaskets were fitted correctly, removed the heads and had them pressure tested and that they were straight now i'm

this one has me beat at the moment.

any sugestions would be appreciated.
BOSSONNOS

**rrrcustom** · 01-06-2007, 09:56 AM

I used to work for GM as a light line mechanic. One of the things we ALWAYS found wrong with cars was that the radiator cap wouldn't hold the recommended pressure. When this happens, generally, the temp gauge will just read high, not overheat, but.....if you swapped the motor, it may make enough horsepower that it actually would overheat. Barring the chance the engine was assembled incorrectly, you could have an air bubble in the cooling system somewhere. Was the system bled correctly when the engine was installed? At the dealership, we used a machine to pump the old coolant out, while refilling it with the new coolant. It's just to difficult to get the system air free by doing it the old fashioned way.

I used to have a similar problem with my '89 5.0 Mustang. No supercharger, but it would get hot in a hurry if I really got on it. Anytime I made a high speed run for more than a couple seconds, the temp would go up to about 3/4 on the gauge. I would get out of the throttle and it would drop. I never kept going to see if it would actually overheat, and when driving conservatively, it would only run at about 1/8 on the gauge(I had a 160 degree T-stat in it.) I installed a 3 row radiator, and still had the problem. I suspect it needed a racing radiator, and a better water pump. My Dad keeps the car now in Missouri, so I don't know of any new issues.

Good luck!

**BOSSONNOS** · 01-07-2007, 09:48 PM

Yep the cap is holding the correct pressure and i'm not getting anymore air in the system, I've run it without the blower belt, now we are removing the intercooler and leaving the blower belt off to take the blower out of the equasion alltogether, if that doen't work the motor is coming out cause it's pissing me off.

Dave

**BOSSONNOS** · 01-08-2007, 03:17 AM

wooohooo fiound the problem, the intercooler is too thick and restricting air flow, removed the blower belt and intercooler and ran it for 40 minutes at 1/2 throttle 3600 rpm in 5th and temp crept up to 230, backed off the load a little and temp came back down.

Thanks for input, i'll post some pics when it's all finished.

Dave

**LS2Tuner** · 01-08-2007, 11:38 AM

Glad you found the problem..... I was going to tell you to actually check the real temp. with temp. gun also. I've found the sensor to be off by 24*.

**BOSSONNOS** · 01-08-2007, 01:09 PM

Originally Posted by LS2Tuner

Glad you found the problem..... I was going to tell you to actually check the real temp. with temp. gun also. I've found the sensor to be off by 24*.

Once I get the new cooler on i will do that anyway.

Thanks
Dave

**LS2Tuner** · 01-08-2007, 06:08 PM

No problem......... Make sure you run RedLines WaterWetter in that cooler instead of anti-freeze........ The more anti-freeze in the liquid the less that the WaterWetter works.....We have got the cooler 14-22* cooler with just destilled water and RedLines additive versus a antifreeze blend.....

Goodluck let me know.