The Stovebolt Site Forums The Shop Area Engine Shop Engine getting too hot before thermostat opens

Hello again, I have another issue with my '53 3100 with a '56 235 car engine. Upon initial start up, the water temp slowly increases up to nearly 220 and pukes out some coolant before the thermostat (180*) opens up, then the water temp drops to 180* and maintains that temp. At first I thought it was a sticky thermostat so I put another new one in with the same result. It's like the thermostat housing stays relatively cool being out in the open up front with fan air blowing on it while the water inside the engine gets hot. By the time heat can radiate to the thermostat to open it, it's too late and the water inside the engine, and near the temp sending unit, is too hot. The water pump heater lines are plugged, only radiator hoses to and from engine. Does there need to be a circulating line of some sort to allow some coolant flow through the engine to equalize water temps and warm up the thermostat?

Sounds to me like you have air pockets in the system. Did the thermostat you used have a small hole in it? If not, then drill a 1/8" hole in it to help burb the air out.....

It has a small hole with a little brass jiggly thingy in the hole. (Highly technical term)

Run a loop of heater hose between the two ports- - - -it will provide circulation of coolant from the head back to the water pump and prevent hot spots from developing around the cylinders. Once the stat opens the majority of the coolant flow will follow the larger radiator hoses and minimize the bypass flow.
Jerry

Make sure you put the correct end of the stat into the housing. I installed one backwards one time long ago in a place far far away and it acted exactly the same as yours.

Hotrod, there are three heater hose ports, one on the gooseneck and two on the water pump. I'm assuming you mean connect a water pump port to the gooseneck port? Rsqwhite, I have the spring down and the pointed end up. I was told that's the way it goes, but I do wonder about it.

Spring should be toward the engine other end toward radiator hose.

Rsqwhite, that is how I have it.

If the heater hose nipple on the thermostat housing is below the stat, that will work- - - -jumper a hose to one of the water pump nipples. That allows the coolant to circulate internally and prevent hot spots due to lack of circulation. Some stovebolt heads have a pipe threaded hole for a heater hose nipple back a few inches from the front of the head, also.
Jerry

I think I cured this issue. I drilled three 3/16" holes around the perimeter of the thermostat. After I fired it up, the temp slowly rose to about 170-180 and stayed put. I think the thermostat was definitely warming up too slow, and by the time it opened the internal water temp inside the block was too high. The three small holes allowed a small amount of water to circulate, keep all the water at a more even temp while warming up, and most importantly brought heat to the thermostat so it could be more in tune with what was going on temp-wise deeper inside the engine. Thanks for all the input guys!

The heater hose bypass would have done the same thing, only with more coolant flow. There's a reason the heater core supply line was on the engine side of the thermostat- - - -it allowed for at least a little coolant circulation, even with the heater control supposedly in the "cold" position. Disabling the heater flow was the main cause of the problem in the first place.
Jerry

I can't believe that is the 'reason'. The radiator CAP does not sense temp.. only pressure.

First, the pressure cap on the radiator would have have lift in order to allow the water to come out.. that will not happen unless the system is at 3-5 (or greater PSI).

I'd take a serious look at the t-stat housing for something blocking the normal t-stat operation.. a casting bur, some slag, something is causing the t-stat to stick. And the built in by-pass hole is large enough to equalize any pressure differential... the build up in the block due to water expanding is not that quick.

Yes, drilling a 3/4in hole in the t-stat allows the water to circulate, but at this point you might as well just take the entire t-stat out.

Nobody ever said it was the radiator cap. And I didn't drill a 3/4 inch hole in the thermo. I drilled 3 small holes, just under 3/16" each. I'll go back and re-read my posts in case I used the wrong wording.

Type slowly- - - - -he can't read very fast and he misunderstands stuff on purpose!

Jerry

add up 3/16 + 3/16 + 3/16 is 9/16th of an inch ohh.. you got me. I mistook the 9/16ths as 9/12ths and simplified to 3/4. 3/4 > 9/16 by 3/16th. Nothing a little ZDDP in the oil won't fix.

YOU SAID: "the water temp slowly increases up to nearly 220 and pukes out some coolant" the cap does not puke out coolant because it was at 220F. It pukes out coolant because the PRESSURE of the cooling system was above the cap's set point.

Drilling holes in the t-stat means that something is either clogged or broken. 2 dead t-stats are not unheard of.. when its summer time you'll see if the motor keeps cool.

I read everything fine... now I have to go line bore some motors.. right Mr. Lincoln?? hahahahaha

I'm well aware that pressure, not temp, is what causes a rad cap to open. I simply stated that the temp gets up to 220, AND the engine pukes out some water. I didn't say that the 220 temp causes the water to puke out. And a 3/4" hole has more than five times the flow capacity that three 3/16" holes combined have. Sheesh!

With out circulation at the thermostat, the water in the block is going to heat up faster then the water in the thermostat housing. It is going to take some time to transfer heat to the thermostat (remember, no circulation), so while that is going on, the block is going above the thermostat setting. Once the thermostat has enough heat to open, the rush of hot water will cause the radiator to spill out due to high heat and pressure. After a brief time the system averages out and works as normal.

No blockage, or broken parts, just a incomplete system.

If the heater hoses were attached, or the heater core bypassed with a loop hose, this would not be a issue. Water would circulate around and under the thermostat creating a smooth even heating.

The owner created his own bypass with three small holes. Its working, he's happy, and the truck is happy. The only down side to drilling a lot of holes is you can slow down the heating up of the engine.

What's so hard to understand?

Joe

But the radiator is designed for that scenario. The upper tank (the copper/aluminum part that has the cap on it) contains a built in accumulator of sorts... if you service the cooling system properly and fill the radiator to the proper level the air gap in the radiator tank contains more than enough volume to to mitigate this initial start up pressure surge as you describe.

Also t-stats are not water/air tight seals, and the check valve for air is also going to equalize pressure.

Your right, it's not hard to understand.

What I would like to understand is how drilling holes in the t-stat is an acceptable solution. For the cost of a tow, or the possible damage caused by an overheated motor I would want to know why I had to drill holes and bypass the t-stat. Is there a crack in a cylinder/head pressuring the water jacket? Is the t-stat housing damaged? Is the water pump impeller worn (happens more than you think)? Is there a family of mice now entombed in a watery sarcophagus?

if OP is happy, then Yay!. But it would be interesting to know the root cause... for science and what not.

There is no "what not" in science. Just science.
I will have to say that quick fixes that ignore root causes can be a mistake. Therefore I am in agreement with the p-man on this point.
Now just don't get all big-headed on me.
Carl

Ok, why is the water temp getting up to 220 before the thermostat opens up?

Lemmm, you're fine now, don't worry about tryin to make faber understand that what you did is what is usually done, and has been recommended in dozens of threads here .... many [most?] thermostats now even come with a small bypass hole already in them, making 3 is overkill, but it certainly won't cause any problem

Bill

Actually the total area of three 3/16 holes is about the same as a 21/64 hole. A 9/16 hole has about 9 times the area as a 3/16 hole.

Ever wonder why the engineers who designed the engine put the heater hose nipples where they did? Could it be so there would be some coolant circulating from the block to the thermostat ALL THE TIME? It's funny how assembling it the way it was designed just might make this whole whizzing contest totally unnecessary!
Jerry

What if it was ordered without a heater? Is there a special bypass hose to connect the 3 ports? A loop of heater hose seems a bit awkward.

Dennis

Dennis, if it was ordered w/o a heater [common] there would have been pipe plugs in the threaded outlet holes, no hose loop is necessary there, although finding that 'awkward' loop of heater hose on one isn't unusual when the heater sprang a leak

Bill

I have been dealing w/ a similar issue the past week or so ...

Replaced:

T-stat three times
Belt tensioner - idler pullies - serpentine belt
Thermal fan clutch
Water pump

I also had a professional shop completely backflush the block & radiator

I had the ac system evacuated & recharged


While all that probably needed to be done pretty soon,
turns out I had a partially collapsed lower radiator hose that was restricting cooolant/water flow ...

Sometimes it is the little things that lead to a larger problem ...


Jim

What am I missing? If water pump is working correctly, and has proper level of fluid in the radiator when engine is shut down at operating temperature, block is completely flooded and water had been flowing across tstat. Now engine cools and is restarted. Water pump pressures up block water level to Tstat, but until block temp gets to 180 in this case, and special spring which expands at 180 elongates, opening passage and full circulation is once again achieved. I don't understand why having partial warmed coolant on the backside of the Tstat is necessary, unless it takes 220 deg to offset the cold backside and get the avg temp on the spring (or the entire tstat housing as Joe and Jerry say) to 180. That would be consistent with heater hose loop and the small hole solution.

What you are missing is the fact that water is not circulating up under the thermostat. The t-stat is mounted in a housing that is up and away from the block like all of them are. The only heat getting to it is from heat soak. The water is not moving across the thermostat, it has no where to go. The small air bleed hole that is standard on most thermostats is not enough, the water in the block simply heats up to fast. By adding a heater core to the system or more air bleeds, the water can now flow across the bottom of the thermostat heating it and the block evenly. Lots of engines do the same thing, most just don't notice it or think anything of it.
All heater systems are plumbed with hot water out of the top, through the heater core, then back to the water pump, its a constant circulation. In this case, the water exits the t-stat housing so water has to flow right across the bottom of the thermostat on its way to the core.

The fact that this engine goes to 220 only means it is heating up fairly quickly, possibly from running lean, fuel quality, tight tolerances, or poor casting of the block or head, doesn't mean there is something wrong. Since the modification, it's now working correctly.

I see this with my 250. The heater hose has a positive shut off inline, so my temp gauge also climbs higher the t-stat then settles once open. With the valve open the gauge shows an even heating with no spike.

Thermostats need to see hot water on the bottom side only. Inside the spring loaded brass piece is special wax that when heated pushes the valve open. The spring is only there to close it back up. You can have ice water on top and still not effect the way it works, but you must have heat on the bottom. With out circulation, the water simply heats up faster deep in the block then it does up in the t-stat housing. The water pump cannot move water if it has no where to go. The only exit out of a engine with no heater system is through the thermostat or the very small air bleed in the thermostat. There are no internal circulation holes or ports, so water just sits till has a place to go.

If there was a problem with the cooling system, the temp would not settle back to the set level and stay.

Joe

Thanks Joe, I thought it was the spring that opened the T-stat. I've changed a few of them out, but been a while. Didn't realize the wax is the "mechanism". I'm almost there...just to be clear. So when cold engine is started, there is a temperature gradient in the engine...very hot, near the cylinder walls, and very cold up near the tstat. By drilling small holes (or allowing heater core/bypass volumes to circulate cold water out)in the tstat, it allows the cold water to move through the tstat and housing, so the hot water can get up there and open it up. The water temp sending unit is nearer the cylinder walls, and registers the hotter "core" block temps. As the cold water gets out of way, and hot water gets to the tstat (flowing vs. heat dissipation) it opens, and system equalizes.

More modern cooling systems than stovebolt engines incorporate various types of internal coolant circulation when the stat is closed. Small block V8's have an extra hole in the block on one side of the water pump that allows a small volume of coolant to circulate and eliminate the hot spots around the cylinder walls. Other engines have a fairly large passageway directly below the thermostat that is closed by a disc on the bottom of the stat once it opens, redirecting the flow toward the radiator.

The idea behind creating coolant flow past the cylinder walls and back to the thermostat is to reduce or eliminate the possibility of coolant boiling around the cylinders and creating enough pressure to override the pressure spring in the radiator cap. This can happen in a matter of a couple of minutes or less if the coolant doesn't circulate inside the block and cylinder head.
Jerry

You have it Allen. One more bit of information. The blocks and heads have smaller holes up front then they do at back of the block ( or less up front and more at back) for coolant transfer from one to the other. Since water takes the route of least resistance, you have to choke it down up front to be sure you get enough coolant to the back of the block. If all the holes were the same size, water would flow in the block and right up and out without ever getting to the back, then you would have all kinds of heating issues.
Not knowing much when I younger, I opened up all the water holes in Pontiac V8 thinking how well the water was going to flow. That engine ran hot all the time, I know why now, back then I thought it was a thin casting or poor tuning.

Joe

One of my students learned that the hard way on a Ford 351W. He opened up the front of a head gasket to match the shape of the water port in the heads- - - -instant overheat! The back end of the gaskets had a big hole, which produced the right flow to the back of the block, then forward in the head.
Jerry

First, I don`t mean to high jack the thread I apologize if so. This is why I like this site so much so much great information here. I`m glad this subject was brought up. I`m in the process of firing up the 1955 235 engine. I don`t have a heater, I plug the thermostat and water pump side outlets. After reading the discussion, it stands for reasoning to have that even flow under the thermostat. I purchase 5/8 hose, the heater extension 3/8 threaded nipples and a dummy heat control valve. From the thermostat housing and water pump the heater hoses would travel like if it were going to the heater. This gives the appearance of it and not having a short loop connecting the pump and thermostat. I know this is alittle over kill. The dummy heat control valve connects the two lines together circulating the water back. I`ll mount it somewhere under the battery holder on the fire wall. Again Lemmm117 I apologize bringing my story in your post. I felt I had to bring it up. Steve

Steve D, no problem. I'm curious, if you were to close your heat valve then start your engine from cold, if you would have the same result I did. But something tells me that you wouldn't want to do that. Good luck.

Update on this topic My 52 3100 with the 1955 235 engine. I notice it was getting hotter on the gauge showing 195 degree as the weather started getting warmer. Everything on the truck is new or rebuilt, US radiator, adapter plate for stock water pump relocation.
I was using a 216 fan blade, I decided to locate a stock fan for 52 235 truck also notice the belt had some play. I purchase a size smaller fan belt so I had some adjustment. I checked the thermostat 180 it was working ok. I did put a 3/16 hole on the thermostat
as discuss earlier on this post. Also I check the timing and adjusted a little which proved the performance. While I was had it I installed a Billet aluminum overflow reservoir, which limited the embarrassing coolant puking when I would show up at events.
Now with the weather at 113 degrees, the truck runs at 185 no problem, even in slow traffic. The main thing I believe was the correct fan blade which is less then 3/4 from the radiator. Also the other things I did help too. The only time I use the pusher fan is when I`m climbing a steep road. The starter kicks over very easy after running the truck for sometime and only been sitting just a short time. Hope this might help someone else that has a similar problem.

You might want to play with the timing

I did, as I stated in my post. The truck is running great and maintaining temperature 185 even in slow traffic. The main thing I corrected I believe was having the correct Fan blade. The other things that I did also improve the truck to handle the 113 degree weather.

Hmmm, interesting conversation. I've owned my 54 3100 since 78, rebuilt the eng twice each time with a new thermostat last time in 87. The only over heat I've had was a timing issue. In all my years as a automotvie techincian I've never heard of drilling a t/stat to make a system work better.wasnt in tsb's or service manuals.. I don't get it.... .A few years ago I installed a coolant shutoff valve to the heater so that it didnt pump hot coolant thru the heater in the summer. Have never had a problem with a disrupted coolant flow causing eng warm up issues. It also helped to stop the small coolant leak in my heater core! I wont reexplain how the cooling system because in all the discussion it was explained and in my thinking as I read thru, there wasnt a problem except for the external issuse. I believe our brains overthink things and we over look the simple things. Always go to the basics and work your way up. Ive got stories of hours wasted to fix a problem that should have taken a few minutes. Some my own and some by others.

The hole drilled in the t-stat eliminates the air pocket from remaining in the head after a coolant change, which will cause over-heating. FLAPs sell one with the hole already in it.
Carl

Joe is exactly right with his description. This yoyo effect is called thermal shock and it can cause some serious problems that have not been discussed here. Most engines suffer from this problem to some degree, but Stovebolts are especially prone to it because of the thermostat location as Joe described.

Drilling holes in the thermostat may not be a very elegant solution but, it is effective. In fact my aluminum radiator came with instructions for doing exactly that to prevent thermal shock from damaging the radiator. Also Ron Davis Radiators states in their installation guide "Aluminum radiators must not be subject to pressure surges that result from air pockets in the engine. When air surrounds a cylinder or area next to a combustion chamber, the metal becomes very hot. When water comes in contact with the hot metal, a volume of steam is produced that is larger in pressure than the cap can release. The resulting pressure bulges the tubes in the radiator and reduces the airflow and cooling capacity."

This thermal shock works the other way too and can wreak havoc with the engine. That is why GM installed a crude but effective 2 stage or bypass thermostat on the 261 engines. Since the cylinders are Siamesed on these blocks there is no water flow between them. This resulted in steam pockets building up which produced localized hot spot that cracked blocks and heads. The cure was to drill steam holes between the block and head and install the afore mentioned bypass thermostat thus insuring constant water flow through the engine. Thermal shock can also cause abnormal and excessive wear on the cylinders and rings. Engines are designed to run in a specific temperature range and running them too cold is nearly as bad as too hot. Anyone who has torn down many engines and measured the wear on them knows that the front cylinders almost always show more wear than the rest. This is because they are operating at a lower temperature than the others. In fact some savvy engine builders hone the front cylinder slightly larger to compensate for this. On my 1958 Apache 235 I have seen the temperature climb to 220 degrees (195 degree thermostat) on initial start up in the morning. Then I have watched it plummet to 160 degrees in a matter of seconds as the thermostat finally opens and a slug of cold water rushes into the engine. I can only imagine what is happening to the front cylinder when this happens. Cold climate or a mechanical fan or an electric fan that runs constantly will amplify this problem.

These are some of the reasons all modern vehicles have some type of bypass thermostat or heater bypass system. Since I am using a Robert Shaw "balanced thermostat" that doesn't easily lend itself to being drilled and the fact that drilling the thermostat slows engine warm up I decided to use a more modern fix. I installed a " AC Delco 15-5675 Heater Bypass Valve" on my truck. It is inexpensive, OEM quality, and easy to install.

I apologize for the long post and the info is worth exactly what it cost you, but it is based on many years of working on classic cars and some of the most famous race cars in the world. As with all the info you read on the internet you should do your own research before you decide what if anything you should do.

Thanks, Diceman