Block temp before thermostat opens

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Oldgearz

Senior Member
I installed a Precision thermostat housing with a 160 degree thermostat. I measure a block temp of 425 degrees on #4 cylinder block before the thermostat opens. Then it drops to 160 when thermostat opens. Should I be worried about engine seizure on #4 with the 425 degree temp?
 
No.

You can always enlarge or drill more bypass holes in the thermostat to speed up the opening.

What does your modern car do in this situation? Let’s not over worry about something that doesn’t exist. More modern cars face this everyday and function just fine without a single thought.
 
Thanks Hitman. I just restarted car and this time didn't get temps above 250 degrees. Maybe first try the new thermostat was stuck closed longer than should be. The Vintage Precision housing has 2 bypass holes built in, so I drilled no holes in thermostat. I'll test again later. Engine temp by gauge never went over 155 degrees. It's only 20 degrees out though.
 
correct me if i am wrong, but according to my knowledge there is a major difference between the way model a thermostats are incorporated and the way they are built into modern engines. in modern engines, the thermostat, if the engine is cold, closes the path to the cooler but opens a bypass. Once the engine is warm, the bypass is closed and the path to the cooler is opened. Therefore there is always water flowing through the engine and the heat in the engine is evened out.


In the model a, if the engine is cold, there is no water movement and therefore no dissipation of heat between different parts of the engine by water flow.
 
TomInCologne said:
correct me if i am wrong, but according to my knowledge there is a major difference between the way model a thermostats are incorporated and the way they are built into modern engines. in modern engines, the thermostat, if the engine is cold, closes the path to the cooler but opens a bypass. Once the engine is warm, the bypass is closed and the path to the cooler is opened. Therefore there is always water flowing through the engine and the heat in the engine is evened out.


In the model a, if the engine is cold, there is no water movement and therefore no dissipation of heat between different parts of the engine by water flow.
Click to expand...

I think drilling extra holes in the thermostat goes a long way to overcoming that. Two extra 1/8" holes is considered the normal but I see no reason to limit it to two. That would give more coolant circulation on start up so the hot spot at the back of the engine gets more cooling. Once the thermostat opens, they would have no affect anyway.
I'd like to see how hot the back of the block gets with no thermostat.
BTW, if the temperature back there did get to 425°, the coolant will have been boiling for a while. With the T'stat closed, that would build up pressure in the block. That pressure would be carried back to the radiator via the return tube. What could possibly go wrong??
 
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Tom..... I believe you are right and wrong. In an A without a thermostat there is constant full flow of water to engine. In an A with a thermostat, there is little to no flow until the thermostat opens. That's why people drill holes in the thermostat to permit some flow before the thermostat opens. In my case, the Antique Precision housing I installed includes two small bypasses built into the housing.....but I have no idea if that provides adequate bypass flow to prevent #3 and #4 cylinders from overheating.
 
Maybe Antique Precision could answer this question? Thay built it, surely some thougt and testing went into the design development? You think?

Dave
 
I have a winter thermostat and a summer thermostat. For the thermostat to operate correctly there has to be some flow. For my winter thermostat I drilled the hole larger, to 1/4 inch. For my summer thermostat I drilled 6 holes 1/4 inch diameter. Before I did that, in the summer, the engine would get really hot and then the thermostat would open and a slug of hot coolant would flow through the radiator. The thermostat would then close again and the process repeated. The increased flow does two things. It keeps the engine at a more uniform temperature front to back and it flows coolant past the thermostat so that it more accurately senses the temperature of the coolant. In the winter I have the ball valve that flows coolant to my heater open so there is always a moderate amount of coolant flowing. The take off for the heater is before the thermostat so the heater gets the first hot coolant. Nice and toasty in the car.

The small hole is there only to evacuate air when the cooling system is filled.
 
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I had a thermostat, but then the engine rebuilder told me he prefers not to use one, due to engine hot spots, so I removed it, and just use half a piece of cardboard in front of the radiator for winter use.
 
I called VP but didn't get a clear answer. We talked about the bypass holes in the housing casting. In addition, the thermostat that was supplied (MotoRad 160 degree) has about a 1/8" hole with a floating brass plug in it that looks like its purpose is to let coolant flow backwards down the upper hose when the engine is turned off. I asked if I should remove this floating loose fitting plug and the answer was "NO Need To". I talked with Casey, the son of the man who invented the thingy. The Dad was busy milling additional housings. My engine has about 10,000 miles on it since a professional rebuild by previous owner. He had an in-line hose thermostat with 1 hole (little bigger than 1/8th") that had migrated to the top of hose (no clamp on it). So the car has been doing fine for a bunch of years with that one hole thermostat in the hose.
 
Just a reminder.

Both the Model T and the Model A cooling system used syphon for cooling.

In the Model A they added a water pump, but unlike modern cars, it was placed at out flow on engine. New cars have it placed at the inflow, forcing the water into the block.

There are owners who believe that some of the problems today with rebuilt engines is the adding of thermostats. Restricting coolant flow to the back of engine.

I am neutral on what every anyone wants to do to their cars. Do your thing.

Mine will stay stock, after 90 plus years, no need to make change.

Enjoy.
 
I have a thermostat with no holes drilled in it after reading all the posts about 3-4 running warmer and a question about shock temperatures I did some testing of my car.on a day in the upper 80s.
after 40 min of idling #1-196 #2-197, #3-200 #4-204
after mellow ride around town --#1-189 #2-184 #3-183 #4-182
after 20 min at 50+mph---#1-183, #2-180 ,#3-175, #4-182
the shocks started at 89 after the 20 min @50+and hitting every bump in the road i got the shocks to 117
When I had the engine apart i paid a lot of attention the the water passages, reamed the small steam holes with drill---after looking at engine cores these holes are 1/2 blocked by rust in most of the blocks. ---perhaps this is the reason for large temperature differences ,remember the cooling system is listed as pump assisted thermo syphen ---a water pump will move coolant through the path of least resistance ,thermo-syphen has to move the coolant through the 'backwater" areas and any partial clogging of the passages will slow that.
 
Good afternoon...I spend one day a week volunteering in a shop tearing down Model A Enginees that have come in to be rebuilt...or engines purchase from God knows where...it seems that the most junk in the cooling systems is always found across the back of the block and head. It takes a bit of doing to get those blocks cleaned out. The point is that the water circulation problem in some engines is caused by too much accumulated junk in the cooling system...not just the type or lack of a thermostat. Ernie in Arizona
 
I installed a thermostat and bypass after the car continued to overheat on hot days even with a well rebuilt radiator. Made all the difference in the world — no more scary temps.
 
Thanks to everyone. Henry didn't put in a thermostat....but then Henry didn't know everything. If he did, he would have used an alternator and 12 volt, the carburetor would have an accelerator pump, you would have hydraulic brakes, a fuse block, a rear gas tank, a battery you could get at....and a thermostat. Just my opinion!
 
Tom Endy said:
Myself and several others had an engine fail with the #4 piston overheating due to a thermostat. I wrote the attached article. However, many in the Model A kingdom do not agree with the theory. I for one will not run a thermostat in a Model A. Five milloin Model A's roamed the planet without them.

Tom Endy

http://www.santaanitaas.org/wp-content/uploads/2014/08/Thermostat-Theory.pdf
Click to expand...

Tom, I am not doubting what you say but how in the world did your engine stay below 160° with the thermostat closed and no circulation? My temperature gauge starts risings almost immediately after I start up the engine. And as you indicate, you must have had your engine running quite a while to be "cruising along at 60 mph".

The reason I run a thermostat is because in my opinion my engine runs too cold, ~140°F. I did open up the holes to 3/16" to ensure there was circulation at startup.
 
Y-Blockhead said:
Tom, I am not doubting what you say but how in the world did your engine stay below 160° with the thermostat closed and no circulation? My temperature gauge starts risings almost immediately after I start up the engine. And as you indicate, you must have had your engine running quite a while to be "cruising along at 60 mph".

The reason I run a thermostat is because in my opinion my engine runs too cold, ~140°F. I did open up the holes to 3/16" to ensure there was circulation at startup.
Click to expand...



I have a very efficient radiator in my car. It has four rows of tubes. On a drive from Huntington Beach to Palm Springs it was very cold, and the temp never reached 160. Halfway there the #4 piston seized.

Tom Endy
 
Took my 1930 CCPU out of the garage yesterday and started it up and let it fast idle (1000 RPMs) for 30 minutes. The outside temperature was 38 degrees. I measured the block temperature before the thermostat opened and #4 was at 181 degrees and cylinder #1 was at 167 degrees. I am running a 160 thermostat with a 3/8" bypass tube routed from the VP thermostat housing to the rear of the block. After the thermostat opened temperatures at #1  didn't vary much from the "before" readings.
 
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