How hot is too hot?

I think your last point is key here. The cooling system was designed for a little over half the horsepower we can make now easily. There has to be a wholistic approach. If you want to make “modern” power you need “modern” cooling to be able to utilize it. That means modifying the cooling system. I don’t know that anyone has done a comprehensive evaluation of the stock setup with the power levels we routinely run now. People have tried this or that but I have not seen a thorough study.

None of these problems are new though. Ask the Ecoboost guys running a tune how hard it is to keep those cool. The extra heat from the turbos does make a difference.

There was a guy here locally, that like EVERYBODY with a turned up 7.3 (that pulls weight) was dealing with hot temps....to the point of ruining engines. At that time, my thought was that the water pump on these is really underdriven. He was able to machine a pulley (serp setup) that made it 1 to 1, and the fan also bolted solid to this pulley. I never got to see this pulley, but he said he had zero issues after doing this. And this was a heavily loaded pickup.

I ran my truck for a summer with no stat, which really didnt help max temp much, and then with the bypass blocked and no stat. with the bypass blocked and no stat, it would take about 30 miles with load to get up to 190 ish, and would not could not get it over 215. It has been along time, but and i dont remember if it was 215 for sure, but I remember not being concerned at all ever about temp.

CBRF3 said:

True but our compression is much higher than the 6.5L and our motors have a thinner cylinder wall so we have less surface area to transfer the heat to the coolant and less buffer and our heads are a totally different beast to the 6.5L. The 6.5 had a issue due to lack of coolant passage size and a more compact cooling jacket which was a perfect storm for a steam generator our 6.9 / 7.3 IDI's were built well in the cylinder head department ( 6.9 has a better design ) as far as cooling passages and such but the bypass to the water pump behind the thermostat was a issue that caused the steam runaway issue similar to the 6.5L. The point is once you hit that point it goes into thermal runaway and there is no simple way of knowing when it was starting hince my mod to block that passage with a freeze plug sunk as deep as can to allow the factory thermostat to work properly and eliminate the issue at its source.

I explain it all in this post hopefully its understandable along with offers some very worth while info and advice https://www.oilburners.net/posts/1081415/

Click to expand...

What year 6.5 has a much lower compression ration than a 7.3 idi?

Black dawg said:

What year 6.5 has a much lower compression ration than a 7.3 idi?

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all factory turbo model 6.5l were 18.1:1 our 7.3 / 6.9 idi's were 21.5:1 or 20.7:1 and the naturally aspirated 6.5l is 21.5:1 hopefully that gives you a idea not many of the non turbo 6.5 variants were used and if they were the non turbo variant they converted them to turbo 99% of time.

the 6.5l non turbo was a slow motor making our NA 6.9 / 7.3 idi's look fast the NA 6.5l was gutless and had to push your foot thru floorboard on the throttle peddle to get it to move out of its own way hince 99% were converted to turbo then they did pretty well if could deal with the heat and head gasket issues and that horrible PMD design who in theyre right mind would put it in that hot spot with no active cooling or heat sinking .

Black dawg said:

There was a guy here locally, that like EVERYBODY with a turned up 7.3 (that pulls weight) was dealing with hot temps....to the point of ruining engines. At that time, my thought was that the water pump on these is really underdriven. He was able to machine a pulley (serp setup) that made it 1 to 1, and the fan also bolted solid to this pulley. I never got to see this pulley, but he said he had zero issues after doing this. And this was a heavily loaded pickup.

I ran my truck for a summer with no stat, which really didnt help max temp much, and then with the bypass blocked and no stat. with the bypass blocked and no stat, it would take about 30 miles with load to get up to 190 ish, and would not could not get it over 215. It has been along time, but and i dont remember if it was 215 for sure, but I remember not being concerned at all ever about temp.

Click to expand...

Ty you proved my point that coolant bypass behind Tstat blocked helps a ton with a Tstat also functioning the warm up issue is almost null and void and the motor will run the set temp of the thermostat with no issues and it eleviates alot of overheating issues and stops the steam issue of recirculating steam into the water pump causing a thermal runaway under hard load.

CBRF3 said:

all factory turbo model 6.5l were 18.1:1 our 7.3 / 6.9 idi's were 21.5:1 or 20.7:1 and the naturally aspirated 6.5l is 21.5:1 hopefully that gives you a idea not many of the non turbo 6.5 variants were used and if they were the non turbo variant they converted them to turbo 99% of time.

the 6.5l non turbo was a slow motor making our NA 6.9 / 7.3 idi's look fast the NA 6.5l was gutless and had to push your foot thru floorboard on the throttle peddle to get it to move out of its own way hince 99% were converted to turbo then they did pretty well if could deal with the heat and head gasket issues and that horrible PMD design who in theyre right mind would put it in that hot spot with no active cooling or heat sinking .

Click to expand...

all of my factory service manuals list the 6.5 td compression ratio at 21.3 or 21.5 to 1.

CBRF3 said:

Ty you proved my point that coolant bypass behind Tstat blocked helps a ton with a Tstat also functioning the warm up issue is almost null and void and the motor will run the set temp of the thermostat with no issues and it eleviates alot of overheating issues and stops the steam issue of recirculating steam into the water pump causing a thermal runaway under hard load.

Click to expand...

I dont think completely blocking the bypass is wise, having the coolant flow through the bypass is supposed to make the coolant temps (and engine temps) more even everywhere in the engine......no hot spots.

I wonder what it would take to make a piece that would actually fit the t stat better so that it restricted that flow better.

Black dawg said:

I dont think completely blocking the bypass is wise, having the coolant flow through the bypass is supposed to make the coolant temps (and engine temps) more even everywhere in the engine......no hot spots.

I wonder what it would take to make a piece that would actually fit the t stat better so that it restricted that flow better.

Click to expand...

The heater core is a bypass and the upper rad hose housing above the thermostat is a bypass also so it isn't a complete bypass and the issue isnt the Tstat blocking it when its open its when steam aka a overheat come into play causing the thermostat to close due to flash cooling the back side of thermostat unplugging that bypass sending boiling coolant / steam into the water pump causing cavitation and well flash steam air locking the cooling system and essentially stopping all coolant flow the water pump is not designed to move steam or air and this is where the steam generator and big issue of the design come into play especially when towing heavy and with a hopped up / turned up motor you get seconds to shutdown or motor is dead and my mod eleviates the risk and stops most of the issue.

I want to also point out the coolant temp will be more uniform without the coolant bypass behind thermostat as 1 side of motor will naturally run hotter due to the recirulating factor right to left and the same coolant that is already hot is also used to cool the oil in the oil cooler before going back into the block and transfered into drivers side head again making coolant temp non uniform and allowing for alot of hot spot issues by the time it hits the thermostat test the mod yourself you will see much lower cylinder head temps and even lower EGT temps along with much cooler oil temps under heavy tow conditions.

I did the testing on a engine dyno with various temp sensor locations in the heads front and back both heads and inlet side of oil cooler and outlet side of oil cooler and even at thermostat and lower radiator hose I used a radiator not the dyno cooling stack with factory cooling fan and shroud that was a interesting setup to build I also used a infrared gun to check multiple locations on the motor / heads during the runs and had 4 EGT probes in various locations on the exhaust manifolds and actual exhaust flange then compared it with multiple runs with the bypass un blocked there was a huge temp difference across the board I even had a heater core plumbed into the loop in its normal location that was almost 1 week of dyno testing and around $3000 worth of dyno cost.

I was fed up with overheating killing my motors ( yes turned up and turbo'd and around 250hp+ ) around 10 fried over the years under heavy mountain tows and wanted to find a solution and people said it was a bad idea to block that bypass and well after I tested it myself found it worked well then wanted to make sure I wasnt playing with any major issues later.

Black dawg said:

all of my factory service manuals list the 6.5 td compression ratio at 21.3 or 21.5 to 1.

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http://www.duramaxhub.com/65-diesel.html

CBRF3 said:

The problem is under extreme load aka towing along with upgrades for power and then you get a overheat. The flash steam will cause thermostat to close and then steam is sent directly into water pump thru the bypass because thermostat closed from steam flash cooling. This causes a thermal run away turning the engine into a steam generator and well steam won't remove the heat and then we have seconds to shut it down or well we have a ruined motor because our piston design ( cast aluminum and no steal top ) and fact our compression is so high we end up in the red and then beyond well pistons swell pinch a ring in the ring land and well crack rings and then they gouge our cylinder walls killing our motors or piston tries to seize from swelling and well our inner rods become outer rods and we get a ugly window into side of our block .

the reason the flash steam will cool the thermostat is because the coolant on other side of thermostat is cooler than the steam and steam when it recondenses it flash cools tricking the thermostat to close causing that bypass hole to be open meaning thermal runaway steam is a crazy thing when it flash cools it rapidly takes heat away so much so its pretty amazing to be honest.

The key thing here is when people use a shut off in the heater loop theyre doing same thing theyre dead heading all the water pump pressure. I suggest a ball valve bypass for a heater core not a full on shut off ever you want a slight bit of flow thru the heater core at all times otherwise you get sludge and well acidity build up in the heater core asking for a failure when you decide to use the heater. Who wants to have to change a heater core in middle of winter or have that heater core fail while happily towing up a mountain keep flow in the heater core always even if is just a little bit to avoid this.

Click to expand...

I've seen that. Certain engines can have localized hot spots that would cause the flash boiling scenario. I don't think our IDI's are one of them though.

In my experience, most engines that appear to be flash boiling actually have cracked heads/blocks or a failing head gasket. All of those will all put air in a cooling system, and since air doesn't transmit heat as well as water, the thermostat closes, vapor locking the cooling system, causing an overheat. Or it causes the radiator cap to open, lowering system pressure, causing more boiling.

You can plug it, I don't really care, but drill a small hole in the plug to vent the air trapped behind it when you do so.

Black dawg said:

I dont think completely blocking the bypass is wise, having the coolant flow through the bypass is supposed to make the coolant temps (and engine temps) more even everywhere in the engine......no hot spots.

I wonder what it would take to make a piece that would actually fit the t stat better so that it restricted that flow better.

Click to expand...

I agree. The bypass needs to be there for coolant flow while warming up.

Interesting that you mention a piece on the bottom. Some thermostats actually have a piece or "hat" on the bottom so as to better block the bypass port. Check out this link/picture for examples. https://www.coolcatcorp.com/thermostats/rogues.jpg



(I'm not sure why the picture doesn't display in the thread, it's showing here in the edit box......)

This image is from a website based on 351 clevelands, which I happen to own a few. The correct thermostat for a 351c is in the middle(with hat), and in those engines it's vital that you use that specific thermostat because the one on the left(without hat) will not adequately seal the bypass port when the thermostat is open, which can let enough coolant to bypass to cause an overheat.

Those thermostats above are all highflow "balanced" thermostats. The idi uses the same style thermostat as those above. Parts stores can give you a standard, "unbalanced" thermostat, listing it as an interchange option. Coincidentally, the isb cummins uses a "balanced" type thermostat as well, and I've seen firsthand where swapping in an "interchangeable" unbalanced model will cause an overheat because it can't flow enough coolant.

Booyah45828 said:

I agree. The bypass needs to be there for coolant flow while warming up.

Interesting that you mention a piece on the bottom. Some thermostats actually have a piece or "hat" on the bottom so as to better block the bypass port. Check out this link/picture for examples. https://www.coolcatcorp.com/thermostats/rogues.jpg

You must be registered for see images

(I'm not sure why the picture doesn't display in the thread, it's showing here in the edit box......)

This image is from a website based on 351 clevelands, which I happen to own a few. The correct thermostat for a 351c is in the middle(with hat), and in those engines it's vital that you use that specific thermostat because the one on the left(without hat) will not adequately seal the bypass port when the thermostat is open, which can let enough coolant to bypass to cause an overheat.

Those thermostats above are all highflow "balanced" thermostats. The idi uses the same style thermostat as those above. Parts stores can give you a standard, "unbalanced" thermostat, listing it as an interchange option. Coincidentally, the isb cummins uses a "balanced" type thermostat as well, and I've seen firsthand where swapping in an "interchangeable" unbalanced model will cause an overheat because it can't flow enough coolant.

Click to expand...

351c m and 400 is where I learned of blocking that bypass port. On my cleveland motor i have that bypass mostly restricted, and then the high flow style thermostat. Never had any luck finding the stat with the hat.

Black dawg said:

There was a guy here locally, that like EVERYBODY with a turned up 7.3 (that pulls weight) was dealing with hot temps....to the point of ruining engines. At that time, my thought was that the water pump on these is really underdriven. He was able to machine a pulley (serp setup) that made it 1 to 1, and the fan also bolted solid to this pulley. I never got to see this pulley, but he said he had zero issues after doing this. And this was a heavily loaded pickup.

I ran my truck for a summer with no stat, which really didnt help max temp much, and then with the bypass blocked and no stat. with the bypass blocked and no stat, it would take about 30 miles with load to get up to 190 ish, and would not could not get it over 215. It has been along time, but and i dont remember if it was 215 for sure, but I remember not being concerned at all ever about temp.

Click to expand...

When you run without a thermostat your temp gauge isn't telling a full story.
The unregulated coolant rushing threw the block isn't in contact with the coolant jacket long enough to effectively draw the heat out of the metal so even though you see lower coolant temperatures often times the block and heads are hotter than they would be if you had a thermostat in place

IH-GM IDI said:

When you run without a thermostat your temp gauge isn't telling a full story.
The unregulated coolant rushing threw the block isn't in contact with the coolant jacket long enough to effectively draw the heat out of the metal so even though you see lower coolant temperatures often times the block and heads are hotter than they would be if you had a thermostat in place

Click to expand...

That myth has been proven false coolant cannot flow to fast for the transfer that is a old wise tale regardless the same amount of heat is transferred albeit at a faster rate when the flow is increased the old wise tale about coolant moving to fast thru block and thru rad is false that has been debunked so many times i won't even get into it further.


When more cooler water is pushed across a hot surface more heat is transferred with the higher flow rate this happens faster this has been proven many times and scientifically at that you need to look into the thermodynamics they simply don't work the way you explained.

https://www.cycleworld.com/story/blogs/ask-kevin/a-liquid-cooling-motorhead-myth/ a good read

(((( When flow moves slowly it tends to move in layers that don’t mix with each other. We feel this as the cooling that happens too quickly after we’ve settled into nice hot bath water. Yet stirring the water makes us feel the warmth again. What has happened is that the layer of water next our skin has given us its heat and by doing so has cooled, making us feel less warm. When we stir the water, we bring water from distant layers—which are still hot—into contact with our skin. Ah! Best of all for those who enjoy a hot bath is a Jacuzzi, which rapidly circulates its hot water, constantly scouring away the cooled layers of water next to our skin, and replacing it with nice hot water from deeper in the flow.


In an engine with a large water jacket and slow-moving coolant, the layer of water next to the hot cylinder and head surfaces is quickly heated—possibly enough to boil it—but water in more distant layers remains cool.

When we stirred the bath water to bring distant hot water to make us feel warm again, we created turbulence—random swirling, mixing motion. As fluid flow accelerates, a point is reached at which movement in layers—so-called “laminar flow”—is replaced by turbulent flow. In engine cooling systems, turbulent flow improves cooling by constantly bringing cooler fluid from all parts of the flow into direct contact with the hot surfaces we want to cool.

Heat flows from a hotter object to a cooler one in direct proportion to the temperature difference between them, so turbulent flow improves cooling by constantly bringing all parts of the flow (not just a thin layer) into contact with hot surfaces. This is why making coolant passages smaller to force coolant to become more turbulent has been so successful in improving cooling. The higher the coolant flow velocity is made the more turbulent it becomes. )))))

So by having a higher flow rate there is a higher heat transfer regardless so long as the mediums have a large enough variation which in our cooling systems our rads and such were designed to handle much more heat dump than we can realistically put into them and our cooling fans also were overkill. So our rads and cooling fan can handle even wide open unrestricted flow rate at wide open throttle to adequately deal with the heat dump and flow so this debunks your theory once again about to high of a flow rate for our blocks / heads to transfer the heat into the coolant and this don't even get into our oil coolers again higher flow rate of fresh coolant from the bottom of rad will be more effective than recirculated coolant thru the bypass at transferring the heat and our thermostat is the regulating factor not the bypass.

Booyah45828 said:

I agree. The bypass needs to be there for coolant flow while warming up.

Interesting that you mention a piece on the bottom. Some thermostats actually have a piece or "hat" on the bottom so as to better block the bypass port. Check out this link/picture for examples. https://www.coolcatcorp.com/thermostats/rogues.jpg

You must be registered for see images

(I'm not sure why the picture doesn't display in the thread, it's showing here in the edit box......)

This image is from a website based on 351 clevelands, which I happen to own a few. The correct thermostat for a 351c is in the middle(with hat), and in those engines it's vital that you use that specific thermostat because the one on the left(without hat) will not adequately seal the bypass port when the thermostat is open, which can let enough coolant to bypass to cause an overheat.

Those thermostats above are all highflow "balanced" thermostats. The idi uses the same style thermostat as those above. Parts stores can give you a standard, "unbalanced" thermostat, listing it as an interchange option. Coincidentally, the isb cummins uses a "balanced" type thermostat as well, and I've seen firsthand where swapping in an "interchangeable" unbalanced model will cause an overheat because it can't flow enough coolant.

Click to expand...

all motorcraft / international thermostats for our motors have the plug system hince why these are all us true 6.9 / 7.3 idi guys recomend is the motorcraft / international thermostats for this reason but this system can fail us when steam and air are in the mix due to flash cooling causing the thermostat to falsely closing opening the bypass port and causing a thermal runaway.