Hey guys whats up I've got a little cooling problem with my Z. Last November I took the 305 boat anchor out of my engine bay and put in my 408 sbc with edelbrock performer rpm heads, holley 750 cfm carb, and other stuff to much to list but it is estimated around 450-500 fwhp. Obviously the stock radiator and fans wouldn't have a chance in hell of cooling it. So I bought a new 4 core radiator and dual fans that pull 4600 cfm. I've also got a high flow water pump and no coolant leaks. But for some reason it gets up to 180 degrees and I start to hear valve cackle which means its overheating. I tried pulling out my 160 degree thermostat and that didn't help. I also have tried water wetter and it made a little difference, I think I was able to drive the car for 15 minutes instead of 10. I've tried pretty everything I can think of but nothing seems to work. I would like to think my fans and radiator are sufficient, so is the water pump. You guys have any ideas?

 

did you drill the steam holes in the heads?

 

yes

 

Is that radiator aluminum or copper? I had a copper 4 core unit and had absolutely no luck with it, so I bought a Griffin Chevy universal radiator 31x19 aluminum unit for 189.00 and no more problems in 3 years and that's using my stock fan clutch assemble again. 406 and 408's are kind of prone to overheating from what I have read and been told. Maybe this helps, good luck..

 

Yes it is an illuminum radiator. Its supposed to be for a 500 hp motor to. So I think I'm good there. And these 400 blocks were not designed very well. They have siamese cylinder bores with no water jackets going through like a 350 does. I didn't know anything about this untill I had the motor built. If I had known, I would have built a 383 instead.

 

What does this mean?

Sounds to me like your temp is plenty low enough; too cool if anything. Certainly not hot enough to cause any problems, by itself.

There's nothing wrong with the 400 design. They work fine. I've had several of them over the years, including one in my Camaro for over a decade; no problems with "overheating" at all, with the stock single electric fan system, stock thermostat (195°), stock fan switch (235° or whatever it is), stock radiator; only non-stock part in the cooling system is a Stewart water pump. Works fine. When I had that motor in the car, it would run about 5° above thermostat temp on the gauge on the highway, for hours and hours at a time, with the A/C running or not; and sitting still with the A/C off (i.e. fan only running when the temp switch calls for it), it would heat up to 235° or thereabouts right below the red line, the fan would turn on, it would cool down to 210° (right near the middle line), the fan would shut off, it would slowly heat back up to 235°, the fan would turn on, it would cool back down to 210°, etc. etc. etc., all day long; literally until it ran out of gas. Exactly the same as it did when the car was new and had a 305 in it.

The 400 has water jackets. Only difference between that and a 350, is that the 4 cyl sleeves on each side are one large assembly, instead of 4 small ones; so they "touch" for about an inch or so of their circumference.

180° is NOT "overheating". If the car malfunctions at that temp, then something else is done wrong. Bashing the 400 design won't fix it. Maybe a better approach would be to leave the temp alone for awhile, and figure out what's really wrong with whatever it is that's making whatever this noise is that you're hearing.

 

you need to just fine whatevers wrong with your motor.

180* isnt overheating. 200 isnt either.

as long as you have the steam holes, 400s dont have a cooling problem.

your stock 92 radiator and fan would have cooled it just fine. me and lots of guys making more power then you can keep it cool.. the stock alum/plastic 3rdgen rad is a cheapie upgrade for most cars...

thermostats control the MIN temp.. not the max. so if you ever DO get an overheating problem, know that putting in a lower temp thermostat is NOT a solution.


my suggestion to you is to run the motor so its warm(remember 180 is NOT overheating.. thats bearly warmed up..), and then find out what the noise is.. my first random guess would be valve lash, but honestly you didnt say much as far as describing the real problem of "valve cakle"