What is the max coolant temp you would allow for a 350 with iron vortec heads before shutting it down? What is considered overheating? Also while i am asking what is the max for aluminum heads?  

Cars since the 80's have been designed to run at 220*F I would think they could be shut off at this temp. I will make the coolant temp spike to about 240+ , I don't like how high that is and would consider it the upper limit.  

The boiling point of water rises approximately 3 deg. F for each pound of pressure it is under.  So a 15 lb cap would raise the boiling point of the coolant approximately 45 deg.  If you add that to the normal 212 boiling point of water you get approximately 257 deg before the water boils.  If I understand things correctly the damage to an engine usually results from the coolant boiling out and the engine components getting extremely hot due to lack of cooling.  My thinking is that it would take significantly more than 250 deg. to do damage to an engine.   However that doesn't mean that you should shut the engine off only when it gets to 250 deg. I'm thinking that I would shut an engine down when it gets a sustained temperature increase of maybe 20-30 deg. over design temp.  Remember that you need make some allowance for coming off a a 100 mile trip on a freeway and coming to a stop.  This will make the temperature spike dramatically and you need to allow for that.  I might get a temperature gauge and see what it spikes to when you do the above -mentioned stop.  Then set your max maybe 10-20 deg. higher than that.  There are also ignition shut-off devices that shut an engine down when the oil pressure gets too low or the temp gets too high.  You might want to see what temp they use an use it for a guide.  

I agree with Arca, my original post leans much more to the safe side, the upper limit of what I'd consider safe.  I don't recommend it, but I've driven my 231 V-6 at 140*F for 20+ miles at 70mph (a few times no less) simply because it was not missing, pinging or steaming out from under the car.  I wouldn't shut it down at that temp if I could avoid it, I'd slow down and hopefully cool it some while running first.  Aluminum heads on Iron Blocks I think are a little less tolerant (they warp), but with better alloys and casting techniques they have gotten better than when they were first introduced.  An engine will run at high temps as long as:
1) The Oil Viscosity does not break down to the point of bearing failure.
2) The engine starts pre-detonating (pinging).
3) The gaskets/hoses don't melt.
4) Metal starts to warp.

The cooling system is basically to keep these in check. I wonder if an engine can get hot enough for gas to ignite in the intake......I've always seen them spin a bearing first.  

Let us not forget the addition of anti-freeze into the equation.It is not as thermally conductive as water.That said a 50/50 mix will yeild a boiling point of 235 degrees with a 15# cap. I would shoot for a max temp based on what you are running for coolant.but at the risk of sounding too conservative, I would try to keep engine temp at 200deg farenheit under all but the most extreme cases. Engines run at 195 to 200deg show decreased cylinder bore wear compared to engines that run above 200deg.Also 180 seems to be the lowest limit regarding bore wear.Unless you run Ethanol/methanol or nitromethane keep your temp around 200deg.The latter fuels burn cooler requireing less cooling capacity.Engines designed to run on those fuels are more heat tolerant as well.Dont forget that a good oil cooler will also decrease engine temps since the oil acts as a coolant as well as a lubricant.Engine oil temps should be kept around 190 to 200deg as well.Even primo dino lube will start to break down above 210deg.Synthetics can tolerate temps around 220 to230deg.As far as temp spikes are concerned, a spike to 220 to 230deg with a 15# cap can be tolerated for short periods of time as described in the above post but watch your oil pressure when this happens.You will probabty notice an 5 to 10# drop at idle at this point with a good oiling system and a tight motor.If the engine is loose(high miles/loose bearings) you will have a bigger drop.With aluminum heads temps around 210 are acceptable.Aluminum does not reject heat very well either but it does transmit it to the coolant better than iron does.Hence the ability to run more compression on pump gas with alloy heads.Heat is taken away from the chamber quicker.V.W. uses an auxilliary coolant pump on its engines to combat the temp spike incurred after shutting the engine off.It keeps the head gaskets from popping.As to your question regarding shut down temp?? If you run a 50/50 mix 235 to 240deg max.if its straight water 250 to 255deg max. Hope this helps,Good luck.  

190's max on a street car.on i easter i fire up the ol' big block,chase the rabbit around then we boil eggs on the radiator,fun for the whole family! here comes peter cotton tail hopping down the bunny trail.......  

In some of the research I have been doing, there is an opinion that compression ratio and engine heat kind of run hand in hand. You can run a higher compression ratio with aluminum heads because they disipate heat faster, which was a new concept for me.  I don't know what your CR is, but if it's 9.6:1 or less with iron heads, then higher heat and predet won't be as big a problem.

I have had some mechanics tell me that the newer cars have to run upwards of 220 degrees in order to make emissions.  That said, I don't entirely agree.  If the engine is designed to run 220 normal temp, then you are going to have problems on hot days, in traffic, with air if you got it.  It all adds heat, and I think 220 is too high a starting point.

I agree with the notion of 190 degrees.  It gives the engine some space to go in a range between 190 and 220.  I am going to change the setup on my Iroc because it gets entirely too hot under stress conditions.  Cool days are OK, but in 90 degree heat, it's marginal.

I have a new radiator on the thing and a regular water pump.  I plan to go with a higher volume water pump, two higher volume electric fans, one that is manually controlled inside the car.  Not exactly stock, but it will help keep heating at bay during hot weather heavy use times.  This worked on my son's RS very well and it keeps a fairly constant 190 degrees with just a single fan.

Hope this helps - Bowser    

I just noticed, in my second post I put I drove my car at 140*F for 20 miles, that's not impressive, it was supposed to be 240*F.

I still say as long as the car doesn't ping (compression ratio plays a major role in this) and the oil doesn't give out (the note about oil pressure drop is spot on) an engine can usually take the heat.  I've seen engines dyno'ed where some made more power at low temp (~180*-160*F) and some made more power above 190*F.  I've looked for a good explaination for the effect of engine temperature on HP (separate from Air Intake Temperature) with out finding any conclusions that I was satisfied with.  

I was trying to figure out how a cold engine could contribute to accelerated engine wear.  

I think the theoretical reasoning behind this would have to tie into the temperature difference across the bore metal, which would change the conditions of the burning and the entropy generation from the finite temperature difference ... thing.  

I drove my all iron 350 for a good ten miles (turning under 3 grand) while it was in the red (blown radiator). I yanked it out and put it in my nova. it ran just fine.