Whats The Optimum Running Temp For An Old Flathead 6??

[drillmastertommy]

I've been rattling around in my old Plymouth truck recently and thoroughly enjoying it! Three and a half years in the putting back together and it's everything I hoped for and more. As per the thread title my question is about what the optimum running temperature of these old engines should be.  

 

Mine is a mildly hopped up 218 currently with a 180 thermostat and after running for a while it will sit at 200 according to the guage, I've no problems with boiling over or puking coolant at any point and I have read in my manual that a 180 thermostat was an option suited to colder climates where a hot water heater was also installed. Starting to open at 180 and being fully open at 200.

 

Today I picked up a new 160 thermostat and plan to fit it tomorrow but after previously reading some info (elsewhere) that stated these engines should be run as hot as possible before the point of boiling, I thought I would seek sage advice from those that have so often supplied it! Supposedly the idea is something to do with crankcase condensation reduction therefore reducing sludge in the engine.

 

I live on the south coast of the UK so it's rarely that cold, never more than minus a few degrees and if we're incredibly lucky a summer may see a 100 degree day (unlikely though).

 

Anybody got any thoughts?

[Niel Hoback]

   I think this topic is one of personal opinion and preference. Alot like politics or religion. We each tend to go with what works for us. That said, as hot as possible without 'overheating", is the most efficient fuel-wise. It also does tend to keep the crankcase cleaner than a cold runnig engine.

  While 200 may sound hot, it really isn't. I personally believe the old adage that "if it ain't losing water, it ain't overheating".  Maybe a little oversimplified, but still, its worked for me for many decades.

  Bottom line, leave the 180 in there and quit staring at the gauge. Turn up the radio and drive on!

[doctor dirt]

I replaced a very old and tired DV 3 (160) with a modern 180. The new one didn't sit right and my temp read out went from 185 to 212 (max gauge). I found a new DV 3 online put it in this morning and the  reading is back to 185-90!!! I think the car is happier there, plus it lives in S.W. Florida now so I think the 160 is the right thermostat!!! Doc

[TodFitch]

   I think this topic is one of personal opinion and preference. Alot like politics or religion. We each tend to go with what works for us. That said, as hot as possible without 'overheating", is the most efficient fuel-wise. It also does tend to keep the crankcase cleaner than a cold runnig engine.

  While 200 may sound hot, it really isn't. I personally believe the old adage that "if it ain't losing water, it ain't overheating".  Maybe a little oversimplified, but still, its worked for me for many decades.

  Bottom line, leave the 180 in there and quit staring at the gauge. Turn up the radio and drive on!

 

I think Neil is correct but I have to admit that I have a 160°F thermostat in mine. But I think, someday, I'll swap it out to a 180°F. In either case it should be fully open prior to the coolant boiling so over heating the on a hot day should not be an issue. My car is starting to show issues with vapor lock on hot days, which I blame on the new formulations they are using for gasoline. But until I get that squared away (by adding the type of heat shield they started using a few years after my car was built) I want to keep the under hood temperatures as low as possible.

[Desotodav]

I have been discussing this point recently with my mate Dave. His normal running temp in his 61 Dodge (318) Phoenix is around 190-200°F. My 52 Desoto truck will run at around 160°F on a cooler day and possibly around 180-190°F on a warmer day. I have not been running a thermostat, but I do intend to run one soon as I am told that the thermostat will slow down the water flow rate a little and give the water time to cool in the radiator. I am also told that a 160° thermostat will work best in our Australian climate as we don't seem to get the high or low weather temps that other parts of the world experience. I recall a while back that I read that our flathead trucks should run around 180°F, but I don't recall whether I read it on this forum or in the Bunn bible. I have to admit though that I am much happier to see my tamp gauge needle positioned more to the left rather than the right.

 

[1941Rick]

Running without a thermostat will exasperate the heating problem. The thermostat opens and closes to control the temp. While the thermo is closed the radiator is cooling the water that is not moving. Usually around 10 degrees. When the themo opens coolant flows into the rad and the cooler collant flows to the engine. Now with that being said if you run without a thermo the coolant does not stay in the rad long enough to cool down. The engine temp then increases and will continue to increase. Remember these cooling systems are non pressure.. I run a 160 with no problems, even when the temps are in the 100's.

[P15-D24]

160 for a non-pressurized system. Why do you want to give up 20 degrees of cooling headroom? These are not the same as todays modern engines which are designed to be run hot.  

[pflaming]

I am running at 160 at 65 mph and getting 14 mpg. I even drove it up to 6,000' from 300' above sea level, in a 35 mile climb and the temp gauge did not move. When I put new pistons and rings in, I steam pressured the inside of the block until only clean water came out. I'm not changing anything.

[drillmastertommy]

Well I haven't changed the stat yet but I have been out for the longest round trip to date and after warming up the gauge sat constantly at 200 as before. It did spit out the extra coolant I put in this morning and is back to the exact level it was at previously.

I am going to install the 160 early this week, if for no other reason than to stop the in cab heater being so effective!

Thanks for all the replies.

[blucarsdn]

I went through an auto mechanic's course in the mid 1950's, I can still clearly remember the training film and text regarding vehicle cooling systems and the importance of maintaining the engine temp at 180 degrees.. This optimum temp had nothing to do with keeping the occupants warm via a personel heater. The optimum temp was to purge the oil and engine assembly of the many contaminants that the combustion process developed..

Old habits die very hard.. In the years prior to the early 1950's, alcohol based anti-freeze, was the norm. Alcohol boils at 180 degrees so the anti-freeze was installed in the fall, drained out and replaced with water, hopefully containing rust inhibitors, in the spring.. Even in today's enlightened world. many people still foster this hangup with anti-freeze/coolant..

In the early '60's, pressurized systems, normally 13/15 lbs, became the normal on new cars.. Pressurized cooling systems raise the boiling point 2/3 degrees for every pound of pressure. A 50/50 mixture of coolant and water with 15 lbs of pressure will raise the boiling point to about 280 dergrees. Of course as the cooling fluid expands it has to have somewhere to go.. I.e., expansion tanks started to become standard on many vehicles, especially those with air conditioning in the late '70's.

As we all know, modern vehicles normally run a 200 plus degrees as a result of emmission requirements, to pruge the engine/exhaust of contaminants.

From my way of thinking, don't let the directions on the can outsmart you, if the manufacure recommended thermostats of a certain value, then why listen to a shade three mechanic. and his theories about what is best for your engine..

A case in point... Several years ago a friend of mine purchased a RV that had a Dodge chassis.. My friend was unhappy with the performance of the vehicle.. He went to a performance shop.. When he got the unit back it was "cold hearted", under full throttle it would fall flat on its face.. The shop had put headers on the 360 V8, (no heat riser) installed a 140 thermostat with water in the cooling system.. The engine was dumping raw fuel into the combustion chamber..

I told my friend to take the unit back to the shop, have them put it back to stock, which he did. 

[Alshere59]

I would think it is more important that your engine gets up to full temperature (oil included) and has a chance to run there, than what temp you have it at. Short trips kill these motors as half the time the oil is still very cool when the engine is shut off. I have done a 20 mile trip to find the oil pan is just warm to the touch.

[SQ4MN]

It is best if you can get these old motors to run at 180 but not imperative. Most of us over maintain our cars since they are much more than just transportation. We tend to change the oil as soon as it seems dirty, usually well ahead of its ability to do a good job. Since we tend to do that the extra contaminants that are caused by running a little on the cool side are flushed out even quicker than a car that runs hotter but doesn't change the oil as often. Its hard to make these engines overheat unless there is a major cooling system problem as they don't make much horsepower and horsepower equals heat. Also they have a good design as far as cooling goes unlike a flathead V8 FORD which because of design is prone to overheat. The stock cooling system is more than is needed if its working correctly. I would suggest running a 180 degree thermostat if it keeps it under 195 degrees I would be happy, but if it goes over that on a hot day I would try a 160 thermostat.

[_shel_ny]

It is best if you can get these old motors to run at 180 but not imperative. Most of us over maintain our cars since they are much more than just transportation. We tend to change the oil as soon as it seems dirty, usually well ahead of its ability to do a good job. Since we tend to do that the extra contaminants that are caused by running a little on the cool side are flushed out even quicker than a car that runs hotter but doesn't change the oil as often. Its hard to make these engines overheat unless there is a major cooling system problem as they don't make much horsepower and horsepower equals heat. Also they have a good design as far as cooling goes unlike a flathead V8 FORD which because of design is prone to overheat. The stock cooling system is more than is needed if its working correctly. I would suggest running a 180 degree thermostat if it keeps it under 195 degrees I would be happy, but if it goes over that on a hot day I would try a 160 thermostat.

 

 

On a hot hay day your 180 thermostat opens somewhere around 180 and if things are hot enough, stays open.

 

On a hot  hay day your 160 thermostat opens somewhere around 160 and if things are hot enough, stays open.

 

Please explain to me how the 160 degree stat will keep the engine any cooler when it keeps the water in the radiator for a shorter period of time than a 180 stat.

 

Edit: fix spelling before Don asks me what a "hot hay" is

Edited October 4, 2014 by shel_ny

[soth122003]

Hey Shel,

 

(Stands in front of a podium with nez-pierce spectacles on)

 

Think of the thermostats as temp controlled relays. The 160 starts to open at 160 and is fully open at 175-180. The 180 start to open at 180 and fully opens at 195-200. The thermostats never really stay open at full open unless the car is going slow or in stop and go traffic or if the temp is above 100 degrees. As the cool water from the radiator enters the engine it will cause the thermostat to start to close and restrict the water flow through it, thus maintaining a steady temp in the engine. These old flatheads put out some heat, but with the big radiators the cooling area is double of the modern cars. Plus the fan is always turning to draw air through the radiator, unlike modern cars with a temp relay switch to turn the fan on and off as needed.

 

I had a 180 in my P-15 and after I took the rad to the shop, they told me the flow rate is supposed to be about 20 gallons per minute. Mine was 0 when the started but they got up to about 10 GPM. They also said to soak the rad in dawn dish soap solution for a couple of days to help clean it out. I did and it worked. After all that fiasco my rad was working good. But because I had a 180 in there I was always nervous about the temp sitting at 195-200. I changed to a 160 and my temp has never got above 180. (I drive 30 miles to work and back 3 days a week) plus my manual calls for a 160 unless I am in a northern climate. I live in the panhandle of Fla. and it was 95 or hotter for the entire month of August and most of September as well.

 

Any way, the thermostat, once eng temp is reached, will never fully close but will slowly close and open to maintain the desired temp by restricting the water flow through the engine. The climate also plays a big role in the cooling of the engine, hot and dry, hot and humid, cold and dry, cold and humid, rain, snow etc... affecting the cooling efficiency of the radiator.

 

You made me type this all out just to see if some know-it-all would answer, didn't you?

 

Any way hope this helps.

 

Joe

[1941Rick]

A thermostat is not an on off switch....It is always cycling between open and closed. When the coolant from the rad gets to the thermostat is reduces the opening thus allowing the rad to do its job and the collant to absorb engine heat. Thermostats begin to open at their assigned value and are fully open above that somewhat.

Make sense?

[_shel_ny]

OK, those 2 posts give me a better understanding of the t stat operation.