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engine over heats, do I need a thermostat?

6K views 13 replies 13 participants last post by  trees 
#1 ·
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?
 
#3 ·
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.
 
#5 ·
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
 
#6 · (Edited)
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.
 
#7 ·
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? :confused:
 
#8 ·
Doc here, :pimp:

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..

Doc :pimp:
 
#9 ·
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
 
#10 ·
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.
 
#11 ·
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.
 
#13 · (Edited)
wyomingoutlaw said:
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?
Assuming the gauge is accurate there are two common overheating events, one is hold temp at cruise and get hot at idle, two is stays within bounds at idle and gets progressively hotter at cruise.

Taking "one" first, this is almost always the result of insufficient airflow across the radiator.

- We've had people using electric fans that were wired backwards blowing out the front that experience heating at cruise and not at idle. If you get pump driven fans cross pollinated between factory V-Belt drive and Serpentine drive, you'll have the same condition as factory style Serpentine
drives turn the reverse direction from V-Belts.

The second one is stickier because there's lots of causes, but in simplicity it's not enough coolant flow getting thru the radiator.

- The same drive issues as above but applied to water pump selection.

- If your running a thermostat, the engine, especially SBCs want a bypass, this allows passage of trapped vapor and eliminates pump and cooling jacket flow separations and cavitation. You can get around this by drilling a couple/ three 1/8th or 3/16th holes in the thermostat, but this adds warm up time.

- The thermostat is there to have control of engine temperature by providing an obstruction to flow to what ever degree is necessary to maintain a proper operating temperature. Wear, pollution, power, fuel economy all suffer when the engine is insufficiently warm. Racers do away with thermostats as a reliability issue and replace them with a washer type restriction. This is only done to remove a simple but show stopping failure point, no more rocket science than that. But racing an engine at WOT for laps on end is a way different problem than driving on the street in all kinds of weather. Contrary to what a lot of racers believe, the most power an engine develops is when it is hot around 200-220 degrees and is inducting cold air, not when the engine is cold. There are so many "rocket science" studies on this for well over half a century that I find it incomprehensible that this idea persists, but it does.

- Insufficient flow the the radiator is caused by:

- Radiator simply too small for the task
- Radiator plugged with corrosion by-products. The cooling system is a
battery where dissimilar metals are exchanging electrons thru the
coolant which acts as an electrolyte. Distilled water and a proper mix
of "coolant" with semi-annual changes will minimize this. The engine,
also, carefully needs to be grounded to the frame to minimize voltage
potentials with in it.
- The use of insufficiently sized electric pumps or the use of underdrive
pulleys. A V8 needs about 10 gallons per thousand RPMs of coolant
circulation.

Other effects especially with custom installations can be a lack of air flow thru the engine compartment especially where air conditioning heat exchangers are ahead of the radiator and or the engine compartment is small and crowded preventing good air movement.

Some fixes for this can be the use of separate transmission and engine oil coolers to take some BTU load off the cooling system. Insulating headers and exhaust systems under the hood. Hood louvers or shimming the hinge if rear mounted to provide an escape route for trapped air. The latter reduces under hood air pressure allowing better fair flow thru the radiator.

Bogie
 
#14 ·
I have written some lengthy responses to this same subject in past threads and for those that use the search function of our board can find those along with some other very good inputs to the theory of cooling our motors and keeping the motor in the right operating range is what we really want. The thermostat and coolant system is designed for that purpose so lets address what is going on in the motor first. Engine heat is basically generated mostly by combustion but is also is generated by friction of all the moving parts. The oil system is there to not only reduce the friction of the moving parts, but to also aid in the heat reduction. Modern motors have built in oil coolers to aid in cooling the higher operating temperature motors. As hot rodders, we should always consider an add on oil cooler, especially as we start increasing the horsepower out put of our built motors. Next, air flow over the motor can aid in the overall cooling especially if there is a significant temperature difference between the air temp and the operating temp of the motor (think air cooled motors). Third, a lot of combustion heat is carried away from the motor through the exhaust system. Free flowing, well designed header and exhaust systems can drastically aid the coolant system in doing it's designed job. Now to the primary coolant system. Heat from the friction and the combustion process is transfered to the coolant system in the motor and the laws of heat transfer are fixed and you must understand them to truly solve the thermostat/no thermostat mystery we keep wrestling with. The coolant must stay in contact with the block/head/intake long enough for the transfer to take place efficiently. Unimpeded coolant flow will not cool the motor effectively and a seriously overheated motor can result and the coolant temperature can stay in the safe range on the gage/light!!! An oil temp gage would be a better indicator of a safe engine operating range. Coefficient of heat transfer has not been mentioned but is important in the efficiency of the system. Aluminum is more efficient(more favorable coefficient of heat transfer) than cast iron or steel and a 50/50 mix of a good grade of antifreeze is better than pure water or pure antifreeze. Most of us know that big improvements have been made in the modern coolants vice the older ethylene glycol or alcohol based coolants.

Now lets look at the other side of the heat transfer operation and that is in the radiator. The same principles apply but there is sort of a reverse action taking place here. The coolant is transferring it's heat to air and the radiator itself is cleverly designed to do this as efficiently as possible. Most radiators are constructed of aluminum or copper tubes surrounded by aluminum, copper or tin fins that are cleverly designed to direct and control the speed of air flow around the tubes to get the best heat transfer from the coolant to the air. Copper, tin and aluminum all have different heat transfer coefficients, but are not drastically different as the cast iron and aluminum found in the blocks. There are different designs of the radiator construction that effects the efficiency as well. Most older radiators had vertical tubes and a top and bottom tanks. Later models tend to have horizontal tubes with side tanks. Both designs have the common design of hot coolant in at the top and cooled coolant returning to the motor from the bottom. Locating fans closer to the top than the bottom is the most efficient way if you have tall radiators. Most of us agree that fan shrouds are an important part of the efficiency equation as well as the distance of the fan from the motor. Regardless, the coolant must stay in the radiator long enough for the heat transfer to take place and this is primarily controlled by the thermostat and is assisted by the size and routing of the tubes. Severe outside air temperatures create challenges for the system. Our Northern friends know that sub 0 temps can result in very low motor operating temperatures, thus air flow restrictors are added to drastically reduce the air across the cooling coils. Some are as simple as sliding a piece of cardboard in front of the radiator or as elaborate as a thermostaticaly controlled "window shade" across the entire front of the system.

Out of all of this, the thermostat is the controller of the entire process. Take it out and you are flirting with an over heated engine and the coolant may not be boiling!!!!

Trees
 
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