Proper engine temp & thermostat?

[kevin h P15]

I installed a new thermostat in the Coupe today. The old one was a convention (modern) stat with no bypass & rated at 195F. The temp gauge was always dead on 195F when warm.

Knowing this was too high for engines of this era, I found a correct one (bypass & temp). Box says it is a 171F, but now temp gauge reads steady 185F. I have the heater bypassed (hoses connected together), but (summer) valve is open on the head.

This car gets only short runs - 5-10 miles at a session, so running warmer is probably better to keep moisture out.

Question - why such a difference in stat vs. temp gauge & should I continue to run with the heater valve open?

[bob_amos]

The difference is because the base engine temp for your engine, and its cooling system, is the 185 degrees that the engine is running at. Because the old 195 degree thermostat was set to a higher temp it would not open and MAKE the temp. rise to reach the 195 mark. To explain just how this works let me put it this way. Without any thermostat your engine would run somewhere near that 185 mark. Putting a thermostat of a lower than 185 degree mark would make the engine reach the thermostats rated temp. In this case that temp is 171 degrees. Now when the engine quickly reaches that mark it opens. Because your engines base temp. is 185 it now continues to reach that base mark. Now, take a thermostat of a higher temp and put that in your engine. Say the 195 degree unit that you were using. Now, that thermostat will remain closed until it reaches 195 degrees. With the thermostat remaining closed there is no circulation and the engines temp. is forced to reach the temp at which the thermostat opens. In this case the 195 degrees. The engine will now continue to operate at that temp. Should the temp go down the thermostat would start to close making the temp come back up to the rated temp of 195 degrees. So, you have an engine with a cooloing system that has its base temp at 185 degrees and you minipulated it up to the 195 mark but with the 171 thermostat you are only assisting it up to the 171 degree mark and the rest of the way up to 185 is the engine and cooling system doing the rest. Got it?

[Guest rockabillybassman]

Could you explain that again, please?

[Normspeed]

Lemme have another sip o' wine and try that one more time.

[bob westphal]

I ran my P-15 without a thermostat all through the summer. The temp would go up to around 185 at the highest but on cooler days stayed below 185. I installed an old thermostat that I've had lying around because as fall and winter approached the temp wouldn't go over 125. Now its back to a steady 185.

[Plymouthy Adams]

For the record..to prevent a lot of build up of gunk in the engine due to low heat from lack of use of thermostat..suggest you keep a thermostat in place at all times..the 185 will get the engine to temp and allow you to cook off the condensation and help retard the accumulation of gunk ..this gunk is notorious for restricting oil return holes in the upper engine starving the car of oil in some extreme cases.

[47heaven]

For what it's worth....my P15 was running hot, even after a cooling system and radiator flush. Come to find out, I had a 195 degree thermostat in there, which caused the engine temp to rise too high. I actually put that one in because it was the one they gave me from Auto Zone. I didn't know about the different tempurature thermostats, at the time. Finally, after troubleshooting, I was told about checking the thermostat, and sure enough, it was the wrong one. I bought 180 degree one from Napa, installed it and the engine temp hasn't gone over 180 since then. Even on the warm days.

[Tim Frank]

Up here in Canada I used to change my MGB t/stat spring and fall.

In summer I ran 160F, winter 190F.

[bob_amos]

Years ago we use to do just that every fall and spring. The old winter/sumer t-stat chenge. It's no longer done due to the fact that todays computerized cars need to reach a predetermined temp. in order to operate properly. In my earlier post did I loose some of you? I was trying to keep it simple but at times I tend to loose touch with what people can digest. When a person is facing me and I explain something I can tell if they are getting lost. Not so in this medium. It's just a teaching trick that I learned from observing my past students. Anyway, sorry if I did go over your head with that answer.

[greg g]

Make sure you put the puppy in the engine right way to. The pellet side goes toward the engine block. By that I mean the business side with the spring and the mystery goo that makes it work needs to be on the engine side. Remember the temp rating is the point at which the stat will begin to open. The closed setting keeps the coolant from traveling throught he radiator till that temp is reached. Essentially this causes a closed loop for the coolant to be pumped through the engine until it opens and lets it travel throught he radiator. I have a 160 in mine but don't drive it from November till March. But I might venture a guess that with the 160 stat, driving around in the winter at sub freezing air temp, with the heater on, the stat might not even open, and that the heater core alone might be all that was necessary to cool the engine, or at least the stat would only just begin to open and allow just a bit to pass through the radiator. I read some where that the heater core on a modern set up will take care of nearly 40% of todays engines cooling at 20F air temp. There is probably more coolant on our blocks and heaters then there is in a new cars total system.

So again the temp on the stat is where it will open, and not an indication of what temp your vehicle will run at. Just for grins after you get it sorted out, buy a cheap thermometer and stick it in the radiator after everything is up to normal running temp and see what you get. This will check your gauge but there can be a 5 to 10 degree difference or so, as the gauge is in the place where the coolant will be the warmest and the top of the radiator will be a little bit cooler.

[Normspeed]

Yeah Bob, I got lost, but I translated it to mean hot is bad, cool is good.

Years ago we use to do just that every fall and spring. The old winter/sumer t-stat chenge. It's no longer done due to the fact that todays computerized cars need to reach a predetermined temp. in order to operate properly. In my earlier post did I loose some of you? I was trying to keep it simple but at times I tend to loose touch with what people can digest. When a person is facing me and I explain something I can tell if they are getting lost. Not so in this medium. It's just a teaching trick that I learned from observing my past students. Anyway, sorry if I did go over your head with that answer.

[Normspeed]

I'm with you Shel. What I don't know would fill volumes!

Mine has a 160 stat, running 50/50 coolant mixture and a zero lb cap although it should be a 7 lb. My book says 180 stat for permanent anti freeze and 160 for alcohol based anti freeze. That's an old book. In my neck of the woods, I feel like the farther to the left I can make the guage run, the more room I've got to get hot out in that CA, AZ or NM desert before I have an old faithful episode.

[grey beard]

There's another little bitty bit of information you'all gents might wish to consider in pondering thermostats and engine temperatures - the speed of warm-up. An engine with no stat will warm up quite slowly, since from the first revolution of the water pump, water will be circulating in the radiator. By comparison to that idea, a stat-equipped engine will circulate only internally - inside the water jacket, etc - UNTIL the stat opens circulation up to the radiator. It is quite likely in my thinking that engines without stats may be driven several miles before any meaningful heat starts to develop inside the crankcase.

Water jacket temperature is the stuff our dash gauges read to us, but crankcase temperatgure is what is critical to keeping a clean engine clean internally. I have seen new vehicles less than one year old with quarts of sludge in the pushrod chaamber due to short runs that never get the block warm. That was on a smog engine of V8 configuration. Our L head flatties are way heavier castings than newer stuff. Translated, this means it takes more time for them to warm up. The temp gauge may say 180 long before the condensation that built up after the last time the engine was shut down begins to boil off. Remember, the only way moisture leaves a crankcase is by evaporation - and that takes heat.

. . . . . . unless it DOESN'T leave because the block never got hot enough - in which case it combines with dirt to produce more of that nasty sludge. Personally, I run a 190 degree thermostat in my 218, and would use a higher temp if it were available. Thermostats of 160-170 degree ranges hark back to the good ole' days of alcohol antifreeze, and for my money have no place in an engine today that runs etholine glycol antifreeze and multi-weight high detergent oil. JMHO

[Young Ed]

It all comes back to driving it. Everyone of mine and dads flatheads has a 160 thermostat in it. There's I think 10 of them now. As long as they are taken out and driven more then 2 blocks to the store they will heat up and evaporate the gunk out just fine. In the summer the higher thermostat seems to leave you that much closer to over heating by the time that hotter water gets into the radiator.

[martybose]

I'm running a real mongrel cooling system on my 47. I've got a stock radiator with a zero pressure cap and a coolant recovery system, no thermostat, a stock NAPA waterpump with no bypass (either internal or external), run 100% propylene glycol coolant from Evans Cooling, and dual electric pusher fans with no engine fan. Even with a zero pressure cap the Evans NPG+ coolant has a boiling point of 275 degrees, so I don't worry about it boiling over and losing some. It starts warming up on the stock temp gauge about 5 blocks from my house, and usually runs between 160-180 degrees. The fans kick in at about 190 degrees, and usually only come on in heavy stop-and-go driving. I've only seen over 200 degrees once; a few weeks ago when I was driving on the freeway and a waterpump bolt backed all of the way out (!!) and dumped most of my expen$ive coolant all over my engine compartment and fenders!

The only problem that I have is that this stuff tries to leak out of every place possible, as it is pretty thin. I've sealed every bolt going into the block and the head, and had to resort to heavy duty T-bolt hose clamps torqued to 100 in-lbs to stop the leaks at the radiator hoses.

As they say, to each his own!

Marty

[bob_amos]

The question was asked about why 185 degrees or whatever temp? Well each system has its own running temp. Generally they should all run about the same if all things could be equal. But, with various conditions being different, such as ambient temp, humidity, just how clean and clear the radiator is, the amount of air flow going through that radiator, the condition of the internal parts of the system.... does anyone see a pattern here? Every little thing and any little thing that might have the smallest bearing on the flow and dissipation of heat from the coolant will change the base temp of a particular vehicle. While most vehicles run close to one anothers base temp any one vehicle would have its own particular base temp. Now, when the system ages that base temp might change. This would be due to changes within the system from deposits and clearance changes from wear and more.The base temp is the free running temp of the system if you did not have a thermostat to control the temp. So why any particular temp? The manufacturers try to design a system that will run in a given designed range and then use the thermostat to tighten those controles on the temp.

[kevin h P15]

I am back - computer down for a few days... The themostat seems to fit & seat well & I cleaned out much of the water jacket when I ground the valves this spring. I guess the box could have been mislabelled - was pencilled at 171, but it works better than the old 195 (thanks Shel).

Does my having the heater bypassed help keep the temp higher? Since I don't have the heater connected, some hot water from the front of the engine immediately returns to the back of the engine - near temp gauge. I will close the "summer" valve and findout.

Since the car is only used for short drives, I think staying hot is better to keep out condensation. I was worried about 195F and too much CTE on such a long engine & manifold. Also lower temp should help with marginal oil pressure.

thanks for the ideas - kevin

[grey beard]

You are absolutely right! AND there are a whole buncha' things that will affect block temperature beside those already mentionee - such as initial timing. Many of us old duffers remember seeing model T and A exhaust manifolds glowing red hot just from retarding the spark. Flathead engines like ours rely heavily on that old water distribution tube. How many of them have been pulled out the hard way and full of mung and nasty stuff that precludes good block cooling. Why, one could play with thermostats until the radiator boiled over and not change the problem if the distribution tube is plugged up. Sorta reminds me of the soldier in "Dandes with Wolves" movie, looking at a settler's bleached bones and saying, "Why dont he write home?"

Then, too, an engine can idle all day and not produce too much heat internally. Put that same critter on a hard, long pull, and cumbustion chamber pressures and temperaturew will skyrocket right now. One thing I have learned from forty-plus years in the business that sorta' flis in the face of a lot of the local wisdom seen on this forum is that when an engine and its cooling ssystem are healthy, it will run better and more efficiently at higher temperatures than at lower. I realize that non-pressurized cooling systems do not offer the margin for extra cooling capcity of high pressure varieties, but antifreeze mix and clean radiators - inside and out - clean water jackets, too - can help to overcome some of this disadvantage. Just because H2O boils at 212 does not mean an engine will not be happy at 190 or higher, with a healthy cooling system and anifeeze. Get an engine warm and its effeciency goes up every time. JMHO

[martybose]

Does my having the heater bypassed help keep the temp higher? Since I don't have the heater connected, some hot water from the front of the engine immediately returns to the back of the engine - near temp gauge. I will close the "summer" valve and findout.

Actually you have it backwards; the hot water comes from the back of the head and is returned to the top of the waterpump, which feeds it into the center of the pump. Effectively, you are bypassing the radiator and feeding hot water back into the waterpump. So yes, close that valve!

Marty