Chronic Overheating Probs

What temperature rated thermostat do you have? Also, you may not have heard of SD (Super Dave), but his advices are legendary. Just because it's new doesn't mean it's good, verify that the thermostat is indeed working. It could be partially blocking water flow by not opening all the way, or not opening at all. I have a warmed over 302, 4 row radiator, NO SHROUD, fixed flex fan, 160 degree thermostat and it NEVER gets over 190 degrees, even in the hottest summer day. Ironically, my car runs hotter on the freeway and cooler in stop and go driving.

I allways used to have heat issues with my 289, with 3-row radiator, allthough the climate is not torpical here in Finland

Now I have 351w, with some goodies, and have no heat problems. The most important factor for this, I think, is custom alu-radiator I had made. Wasn´t cheap but was definetly worth it. Car run´s constant 82 °c (wahtever the heck it is in Fahrenheits.. 9´11? . ...and that is with no fan shroud.

I had some problems with my freeze plugs. The engine was machined in US before I bought it, tore it down and assembled it... Too bad, I thought they had replaced freezeplugs and properly cleaned the block... but nope. While starting the car, I lost one freezeplug and coolant was out.

Luckily freeze plugs could be replaced with the engine on it´s place. I only had to remove enginem mounts from the side I was working on. the reason I´m telling this, is that while replacing those freeze plugs, i cleaned enormous amounts of rusty crap from inside the block... This should be done allways, when replacing new radiator. I was lucky for freeze plug to come off before thermostat had opened and rust had cloaked my new radiator...

, just my 1$ ...

car noob said:

Just a little update, I'm gonna ditch the 14" fan and stock shroud so I went ahead and ordered a new 17" flex fan and one of those plastic shrouds, hopefully it will be here by the end of the week. While I'm installing those I will take a replace the thermostat, it is about 2.5 years old so it could not hurt. Would you recommend a 160 degree or 180 degree unit? Currently I am running a 180 degree thermostat and always heard that if you run lower than the 180 the coolant doesn't have enough time in the radiator do dissapate it's heat. Is this incorrect?

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I would run the stock temperature thermostat. Motors are more efficient when they run at a hotter temperature, until they get too hot and ruin parts. At 160 the motor is running cooler than it should, which means there will be problems IMO.

If you run 160 thermostat, the motor should just run cooler. Your statement about the coolant going through the radiator too quickly doesn't make sense to me. The faster the coolant moves through the radiator, the more heat will be removed from the engine. That's because the rate at which heat comes out is governed by the difference in temperature between the fluid in the radiator and the outside air. If the coolant resides in the radiator a long time, less heat will be extracted from it as the coolant temperature is reduced.

For instance, if the coolant temperature was the same as outside air, no heat could be removed. If the coolant is at 180 or higher, much more heat will be removed as the relatively cool outside air passes through the radiator.

the thermostat(t-stat) only controls the minimum operating temp. Say you have a 180 t-stat and your car always runs at 200, you then swap in a 160 t-stat, guess what your new operating temp is, yep, still 200. This is becaue the t-stat rating determines when it begins to open, one will begin to open at 160, the other at 180. Actual operating temp is determined by radiator efficiency and sizing. The t-stat rating only comes into play if the radiator is capable of cooling the engine to 180 or 160 degrees. Basically, the thermostat is only as good as the radiator. In your case, I think the radiator is your problem-unless, you can find a way to move massive amounts of cool air through it.

Since your a self proclaimed NOOB, heres an analogy. Say your at home on a hot summer day, sitting on the couch-sweating like a pig on the BBQ. You adjust the a/c thermostat on the wall to 60 degrees. What you don't realize is that your trying to cool a 30,000 sqft home with essentially a puny 'window unit' sized air conditioner. An hour later, you're still sweating as your inside temps are hovering at about 85 degrees. Eventually, you come to the conclusion that you need a bigger air conditioner, one that has a higher BTU rating, in order to get the desired indoor temperature of 60 degrees. Just turning the t-stat down doesn't necessarily make the house cooler.

car noob said:

I see what you are saying, but what I said was that with a 160 thermostat the coolant will be constantly moving and will only be able to spend a few seconds in the radiator before being sucked back into the engine so it has no time for the excess heat to be absorbed by the ambient temp outside. As I said earlier this is just what I have been told, and heard on this board a couple times just thought I would get some thoughts on it so what you said is VERY helpful and another reason that I should run a 180, but was just curious if you had any thoughts or concerns on what I heard.

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I'm trying to help. I don't know nearly as much as other members, and hopefully people will jump in if they see glaring errors. I'm just using logic to analyze the question, not experience. I think the thing you read is wrong. Let me try another method of explaining why.

The rate of cooling in the radiator is only dependent on the temperature of the water in the radiator. How fast the water is moving doesn't matter. When the thermostat is closed, the coolant in the radiator could be ambient temperature - therefore no cooling at all. The faster the water is moving, the less variation in temperature in the coolant. So therefore, the radiator will cool more with the water moving faster.

I hope that helps.

car noob said:

^I had to think about what you said for several minutes but I think I've finally got it figured out, hook up the advance mechanism on the distributor to the intake manifold and this will increase the vacuum the distributor see's and bump the timing?

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Sounds dumb, but the easiest way I've seen to check the Vac Advance is to pull off the hose and keep it attached to the advance. Put it in your mouth and suck--if it holds a vaccuum--like a blocked straw, it's ok. If not, your advance is shot. I changed everything I could think of to get rid of a surge in my car. Turns out it was the advance. This proved it.

YMMV.

--Paul

Hack said:

I'm trying to help. I don't know nearly as much as other members, and hopefully people will jump in if they see glaring errors. I'm just using logic to analyze the question, not experience. I think the thing you read is wrong. Let me try another method of explaining why.

The rate of cooling in the radiator is only dependent on the temperature of the water in the radiator. How fast the water is moving doesn't matter. When the thermostat is closed, the coolant in the radiator could be ambient temperature - therefore no cooling at all. The faster the water is moving, the less variation in temperature in the coolant. So therefore, the radiator will cool more with the water moving faster.

I hope that helps.

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the rate of cooling for the radiator is dependent on several things. Mainly, airflow across the radiator, surface area(number of fins per inch), and difference between ambient air temp and coolant temp. How fast the coolant flows through it isn't one of them, but it is very important. Since you can't control outside temps, and you can't really add surface area to your existing radiator, the only thing you can do to improve its performance is to increase airflow.

A radiators performance is measured by how much energy it can dissipate per unit time. Basically, how many degrees it can decrease the coolant temperature per gallon/minute. Lets say your radiator can knock off 20 degrees at a coolant flow rate of 2 gallons per minute. If you then speed up the flow to 4 gallons minute, you will likely only see a drop of about 10 degrees in coolant temps.

If airflow through the existing radiator is good, and all else in in order, the only thing you can do to increase the cooling systems efficiency would be to get a larger radiator that is capable of dissipating more heat.

302 coupe said:

Lets say your radiator can knock off 20 degrees at a coolant flow rate of 2 gallons per minute. If you then speed up the flow to 4 gallons minute, you will likely only see a drop of about 10 degrees in coolant temps.

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With a given outside temperature, radiator, fan, etc., the amount of heat the radiator will remove only varies by the temperature of the coolant in the radiator. The temperature of the fluid in the radiator doesn't matter to the health of your engine, it's the temperature of the fluid in the engine that matters. In your example, the 4 gpm flow will have a more even temperature in the whole system. In other words, the fluid in the engine won't be 200 degrees and that in the radiator 100 degrees. The two temperatures will be closer to the same, which means more heat removed by the radiator and less heat residing in the engine.

Less flow through the radiator is only good if the engine has not arrived at operating temperature yet, or the system is otherwise too cold.

I've always kinda wondered what the coolant temp is when it leaves the radiator to go back to the engine. Anybody know? Ideally, the ingoing and outgoing temps would be as close as possible to avoid any uneven temperature distribution through the block. The best way to control, not necessarily lower, overall system temperature is with a high enough flow rate, I think this is kind of what you are refering to Hack. And I agree, a radiator will cool more given a higher temp difference between ambient and coolant temp. However, the original poster's problem seemed to be that for his radiator to perform efficiently, the difference between ambient and coolant temps was too high, thus the overheating problem. For example, in order for his radiator to dissipate 'x' amount of energy, temp difference would have to be 160. If its 80 outside, his coolant temps will be at a steamy 240. On the other hand, a larger, more efficient radiator would be capable of dissipating the 'x' amount of energy with a temp difference of 100, assuming outdoor temps of 80, his coolant temp would be 180. A larger radiator that is capable of shedding more heat would be able to operate with a smaller difference in temps. This would lead to a cooler running engine, regardless of coolant flow.

Right on.