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Old 07-07-2007, 09:04 AM
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engine over heats, do I need a thermostat?

I built my lemans for the strip, but it still sees an occasional cruise around town. the problem is while cruising around town the temperature slowly climbs to around 210 where I get nervous and shut it down. my temperature sensor is in the intake water crossover, which would be the hottest point, but that still seems mighty warm. I'm running one large electric fan, as I've never had a problem before with electric fans keeping an engine cool. I'm not running a thermostat, but after describing my problem to a fellow hot rodder he told me that is my problem. that seems wrong to me; wouldn't a thermostat restrict the coolant even when it was fully open? or am I missing something? I would just toss one in and try it but my intake sits on top the water cross over making it a bit of a job. what do you all think? are any of you running thermostats in your strip cars?

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Old 07-07-2007, 09:27 AM
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Yes a thermostat in effect will restrict the flow but it will also give the coolant in the radiator time to cool off before re-entering the engine.
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Old 07-07-2007, 10:05 AM
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Do you honestly think all the car manufacturers would install a thermostat IF THEY WERE NOT NEEDED ??? Just think of the millions of dollars Ford, General Motors and Chrysler ... EACH ... would save.

Buy a good brand ( I prefer Robert Shaw ... Summit sells them or did ) thermostat in the 190 range and ENJOY the benefits of a thermostat.

PLUS ... as a side note of information ... most electric fans do not pull as much air as a good belt driven mechanical fan. General Motors uses a belt driven mechanical fan where they can. Look at a full size Silverado ... room to use a big mechanical and the need to COOL a V8 ... General Motors installed a belt driven fan.
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Old 07-07-2007, 10:26 AM
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Car running hot.

I bet it's fixed once you did what other members told you what to do.
Good luck!
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Old 07-07-2007, 11:56 AM
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The thermostat/no thermostat question comes up frequently and the stock answer is that you do need one. However, if the task is to keep the engine temperature as low as possible, has anyone actually tested the two options to see how they compare during normal driving?

Modern engines use a thermostat because otherwise you would never get decent heater output in the winter. Slow warmup also screws up computer-managed engines because the computer keeps them in rich startup mode longer. Overall combustion efficiency is probably lower on a cooler engine. However, if the task is to get the most effective cooling, its seems that higher flow is better. Water that spends less time in the radiator also spends less time in the engine, so the overall cooling ability should not be dramatically different. We get the best cooling with higher air flow through the radiator, so why would lower water flow rate improve cooling?

I am not suggesting that you remove the thermostat. However, I'm not sure it would completely screw up your cooling capacity if you did run without one during the summer.

Bruce
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Old 07-07-2007, 12:45 PM
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Quote:
Originally Posted by HalfOunce
Yes a thermostat in effect will restrict the flow but it will also give the coolant in the radiator time to cool off before re-entering the engine.

and conversly, the water stays in the block longer getting even hotter! LOL

And the discussion goes on and on and on.
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Old 07-07-2007, 01:25 PM
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We recently had a post like this and it opened a can of worms like it always does. But as already said, all the car companies wouldn`t have spent a dime on them if they were not needed. Also as said, it acts more as a timing device, when it`s closed it keeps the coolant in the radiator where it can be cooled off, it can`t cool if it goes in and out within 20 seconds. I`d just install a 180 degree thermostat, on the outer base drill 3 holes about 3/16 or one step smaller in size, this will act as a air burping system to burp all the air out quickly. Another thing is make sure if your radiator has a overflow that it`s connected to a catch can, on GM vehicles this acts as a venting system, if the overflow is plugged off, it can`t ventalate and it`ll run hot, been there, done that. My cutlass had all kinds of overheating problems. Most times when I was filling it up with coolant, I would have the cap off, fill it, start the car, when the level went down, I`d fill it more, then when the thermostat opened fill it the rest of the way, put the cap on, and it would run hot. This was how I always did it and didn`t understand why it was running hot, Then I found the owners manual to my cutlass, it said to fill the radiator with the engine cold, place the cap on, then add water to the "cold" mark on the overflow, start the engine, you`ll see the air burping out of the system in the overflow and then you`ll see the coolant level in the overflow go down, refill as needed, when the engine gets to operating temp keep your eye on the overflow, add more coolant as needed, when it finally isn`t taking in anymore coolant, fill it to the full warm mark on the overflow. I tried it and no more overheating. The bubbles were the indication this is how the vented coolant system GM cars use works. After I did this to my cutlass, it ran a constant 185 and never over 195, even when I ran it hard, I couldn`t have been happier. One last thing, I would move the temp sensor to the head, this is where the coolant is hottest, as this is where all the action of combustion is going on at, in most cases the temp of the coolant in the head is up to 20 degrees hotter.

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Old 07-07-2007, 01:26 PM
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What's the opinion of whether or not an engine can overheat BECAUSE the thermostat is missing? I have heard that for years (water moving too fast) and have been of the opinion that removing the thermostat from a normally operating engine will not cause it to overheat and indeed every single engine that I seen it removed from would not even reach normal operating temperature let alone getting too hot. Is there some circumstances where it would be possible to cause overheating by removing the thermostat?
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Old 07-07-2007, 02:36 PM
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I just may try taking mine out on my truck. My new engine does good but now that the temps are 110+, it's getting to half on the factory guage on the freeway with the A/C on. That's a tad warm but not "overheating". I have a real crappy fan clutch that I use during the fall, winter and spring. I usually install my HD truck fan clutch in the summer but am trying to avoid it this year. I hate the noise and it helps kill off my crappy gas milage even more.

I have run it long ago without and to be honest, all it accomplished was a very cool heater in the winter. But that was my old engine and maybe it's time to try it. Wish I had a "real" temp guage for a better reading, but oh well!

Mark
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Old 07-07-2007, 03:20 PM
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Quote:
Originally Posted by oldred
What's the opinion of whether or not an engine can overheat BECAUSE the thermostat is missing? I have heard that for years (water moving too fast) and have been of the opinion that removing the thermostat from a normally operating engine will not cause it to overheat and indeed every single engine that I seen it removed from would not even reach normal operating temperature let alone getting too hot. Is there some circumstances where it would be possible to cause overheating by removing the thermostat?

My OPINION is as follows:

If the engine is going to truly overheat WITH a thermostat, it will overheat WITHOUT one too. There are a lot of variables in any cooling system. Radiator size, radiator condition, water pump impeller condition, engine heating variables and air flow problems too. In a perfect world, we would all have 4 core almuminum radiators and 4000 cfm electric fans and engines that did not create hot spots in the cylinders or heads or block. But that ain't gonna happen any time soon.

Thermostats:

The thermostat operates on and respones to the ENGINE WATER TEMP ONLY, and does NOT react to the radiator temp. The sensor on the thermostat is on the engine side and as soon as the water temp on that side reaches the rated temp of the thermostat, it will begin to open. Usually, in a perfect world (or when its nice and cool outside), the thermostat will cycle from closed to open some to closed to open some and so on and so on. Once the water temp on the engine side passes the rated temp of the thermostat, it will be fully open until such time that the engine water cools back down. The thermostat will not close to keep the water longer in the radiator, it will only close when the sensor temp drops below what its rated at.

Airflow:

Again, this is a huge variable and some radiators need lots, some not much at all. A good working mechanical fan clutch and stock type fan are good air movers but a real power robber. According to Stewert/Robert Shaw, FACTORY installed electric fans far exceed the needs of the cars they are installed on. Short answer.......electric fans work better than stock fans and free up a LOT of horsepower, but only when matched to the system and demands of the vehicle. True, some big "family" type trucks and SUV's still use mechanical fan clutches and fans, but they are the few and do so because they are often used to pull big loads like travel trailers and bass boats and horse trailers. If not for that, i'm sure a good FACTORY designed electric fan would do fine.

Back to air flow.
The design of the front of the vehicle has a lot to do with airflow, as does the engine compartment. If the engine bay is NOT condusive to air moving through it, a fan is needed at higher speeds. Likewise, if the shape of the front of the car is not good for flow, the fan will need to be on at faster speeds to keep it cool. The old saying of "the fan is not needed above 40mpg" is an old wives tale and just not true across the board! On some vehicles it "may" hold true but on others it just don't fly!

Case in point. My 86 3/4 ton truck. 350 stock. Qjet, dual air pumps, EGR, factory duals and overall a low hp smogger engine. On that truck I have a loaded cabover camper. The truck has to work HARD to move it and the camper down the road. It generates a LOT of engine heat compared to my '77. When cruising around town, the fan is "on" all the time, sucking huge volumes of air. Once I get to about 50 or so, the fan clutch just can't spin the blades any more and gives up. At that point, my engine temp climbs to between half and three quarters on the guage. If I don't hit any long hard hills, it won't usually go any higher. BUT....if it does climb up, all I have to do is slow back down to about 55 and I can hear the fan kick back on and actually watch the temp guage drop back down to quarter, even on a long hill. So the air hitting the front of the truck is NOT suffecent even at 55 or 60 if I really load it hard.

Bottom line is thermostats are used to keep the engine temp UP and constant at a certain temperature. Once the engine water temp goes above the rating of the thermostat, it's open from then on until somehow the coolant cools back down.
Fan clutches suck in my opinion but I don't have the bucks to buy electric for both my trucks. I really don't need them anyway but it would be nice to free up some much need power on my '86.

All the water flow in the world means nothing if there is not enough air flow to cool the water, and all the air flow in the world means nothing if there is insufficient coolant flow. It's a balancing act on both and it will vary from car to car. Some can run with a small fan, others will need all they can get. Some need a big radiator, others not. Some will say that their car runs cooler without a thermostat, others won't. Again, it's a balancing act between the heat generated, water flow and air flow. Most of us don't have the perfect system so we're forced to over compensate in one area to make up for the other area we can't control.

my 4 bucks worth!! LOL

Mark
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Old 07-07-2007, 03:48 PM
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Doc here,

Some Non T~Stat Things were NOT mentioned also...

210 IS NOT HOT! It's right in the ballpark..

That engine , IIRC, and it's been years..sits a Gillzillion miles AWAY from the Radiator..EVEN stock..had a HUGE shroud..Do You?

Is the airflow around the radiator Sealed off? and the flow Through it unobstructed?

Is there a CLEAR path for the hot air to escape from the engine bay? (louvers, Etc..) Hot Air Rises..and Sits.

Is the Ignition system / Timing Even Compatible for street cruise or is it set for "Hammer Time"?

Stock Steel fan will cool much better (in this case, I think) then the electric at low RPMs..

Just some more "Stuff" For the Mix..

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Old 07-07-2007, 07:35 PM
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I have a '75 3/4 ton GMC truck and the heating characteristics are about identical to those of Jmark's '86 3/4 ton. I could leave it idling just about all day and the gauge will stay about about 205 (195 degree thermostat), or I can drive it at speeds up to about 55 mph and the temp won't change. If I try driving at 70 mph, the temp will rise to about 225-230, and will usually stabilize. I have a stock shroud, HD fan clutch, 3 row HD radiator, and stock thermostat.

I've come up with a couple of guesses about what is happening at about 60-70 mph:
1st - my Hayden HD fan clutch is supposed to start to freewheel at about 3000-3200 rpm. For my truck with 4.10 gears and stock tires, that's about 60-65 mph. I think my fan stops pulling at about 60-65 mph.
2nd - I think that at higher speeds the air may be hitting the radiator, deflecting off the flat radiator, and going down between the radiator and the front bumper instead of through the radiator. Without a fan to pull it, there is not enough air flow to get good cooling. I can't find any remnants of a stock air dam, and my repair manual does not show one.

I'm going to try adding a horizontal piece of flat plastic (like a light weight skid plate) to block the gap between the radiator and the bottom of the bumper. That may force more air to go through the radiator at high speed.
I'm also switching to a high flow thermostat, as soon as I can find one locally. I'm currently using a stock 195 degree thermosat with three holes drilled around the edges.
If that doesn't work, I'm going to try adding a supplemental pusher fan in front of the radiator. Some of the later GM Suburbans used that arrangement to help with AC performance.
I also want to manually verify TDC, to make sure my timing tab is right and that I'm not running too advanced.

Bruce
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Old 07-07-2007, 10:12 PM
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From personal experience coolant dwell time in the radiator can be an important factor....provided the radiator has sufficient capacity to be able to dispell the heat to the air.

Within the last week I changed the 160 degree thermostat from my Plymouth to a 180. The end result was instead of a max temp at highway speeds with the AC on of 200 degrees on a 100 degree day I dropped to 190 (the HD fan clutch locks up at 195).

I built a 58 Biscayne with a 383 stroker years ago....around town and at idle even with the AC on it would do fine, on the highway it would heat. I did everything I could think of. Eventually out of desperation I pulled the upper control arn seals (the dust flaps that keep dirt out the engine compartment). It cured the problem........from what I could tell by that was that at speed the engine compartment was not allowing the air out fast enough.
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Old 07-08-2007, 08:22 PM
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Coolant is not cooled by the amount of time it spends in the radiator.It is the air flow thru the radiator that cools the coolant.If you temp creeps up after sitting for awhile you need a larger electric fan,for more air flow thru the radiator or a larger radiator.For more water volume.
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Old 07-09-2007, 06:13 AM
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There's only one way to find out for sure. Put one in. Thermostats are not very expensive and don't take very long to change. Let us know the results.

Danny
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