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Discussion Starter · #1 ·
So I’m at about 3000 miles on my truck now and I’m still working out some bugs. My latest is water temp. I have my water temp sensor in the rear left side of the block. I believe this is the recommended location. My truck is complexly custom and has a side facing radiator. The radiator is very large with two very powerful Spal fans.

Most of my driving has been below 55mph. At those speeds, the water temp remains very low. (170’s) Recently, I have been driving faster due to solving some other issues. On several recent trips, I have been up to 60-65 mph. At those speeds, the temp gauge will slowly climb up to about 230. If I pull over and let it idle, it will cool back down to 170 in a matter of a minute. But if I continue above 60, it will climb up again.

I don’t know if it’s important, but it has never over heated. When I say overheated, I mean it has never blew steam. I have a recovery tank and the level never changes. It would seem like 230 would have to boil. One time I ran it to 230 and pulled over and pointed a temp gun at the radiator outlet. It was like 150. I wish I had pointed it at the inlet, but that’s not as easy to access. Can the coolent be 230 in the block and 150 coming out of the rad?

Do you think running the rear block at 230 will damage it? The motor seems to be running fine. For background, my 4BT has a HX30w with the fuel turned up some. At 62 mph, my EGT is running 1100. (RPM’s are around 2300)

Any ideas or comments welcome.
 

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what thermostat do you have in it and do you know what the temp is at the outlet. as for 230 in the engine and 150 coming out of the radiator yes you can have that. are you sure the radiator is clean and has no restriction. how is the airflow thru the radiator getting out from it since its sideways.
if your seeing 1100 degs on egt what kind of load are you putting on this.
 

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Discussion Starter · #3 ·
what thermostat do you have in it and do you know what the temp is at the outlet. as for 230 in the engine and 150 coming out of the radiator yes you can have that. are you sure the radiator is clean and has no restriction. how is the airflow thru the radiator getting out from it since its sideways.
if your seeing 1100 degs on egt what kind of load are you putting on this.
The thermostat is stock. ((I think 190) Raddiator is brand new as is the water pump. No real load except aerodynamics of a brick.

The air flow goes from under the truck through the rad and out the side. I wondered if maybe at 60 the air flow outside the truck might be blocking the flow out of the rad. Also, I theorized that heat coming off the turbo might be sucked in the radiator. I just ran the truck with the engine cover off. This should greatly disturb the air flow around the turbo. I drove the truck at 60+ for quite some time. While the temp never got to 230, it was over 210.

When I got back from this drive, I went all over with a temp gun With the truck idling. One thing I noticed was the inlet and outlet of the radiator was about 115 degrees. I put my hand on the stainless pipes and they didn’t even feel warm. (It is about 90 out) The exhaust pipe was about 150 and the turbo was about 450. I put my hand about one inch from the turbo and it wasn’t real hot. I was thinking about a turbo blanket to protect my motor mount, but it’s 6-8” away. I guess that turbo is a lot hotter when running at speed.

The area where the gauge sensor is threaded in did read about 170 which was on the gauge. So I guess it’s accurate. Everything else seem to be cooler than expected. At this point I’m wondering if my thermostat is sticking. It was new when I first started driving the truck, but sometimes you get bad ones. I might just pull it out and leave it.

My other thought is to reverse the fan direction and suck from the side and blow out under the truck.
 

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Something is off somewhere. 230 deg is super hot. The rear position on the head is the hottest point on the engine. Usually, the temp sensor was in the front top point near the thermostat and the cooling fan sensor was in the rear one. Either way, that doesn't explain why yours gets so hot so quick. Second, 1100 deg EGT is way too hot for just running down the road with no huge load. That should be near the max with a heavy load. Normally you'd expect somewhere in the 600-800 deg range. Also, why such high RPM at 62 MPH. Are you running a super low gear ratio rear end. At that speed most try to hit around 1800 RPM. Your fuel economy is going to be horrible running that high RPM at normal cruise speed. By the way, normal thermostats for the 4bt/6bt are set at 83 deg C or 180 deg F.
 

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By pull and leave the thermostat are you meaning to leave it out? You have to have one in there to block the bypass when hot.
170 is way too low for a normal operating thermostat. Check the temperature at the outlet on the head and either side of the thermostat when it running hot.
 

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Discussion Starter · #6 ·
Something is off somewhere. 230 deg is super hot. The rear position on the head is the hottest point on the engine. Usually, the temp sensor was in the front top point near the thermostat and the cooling fan sensor was in the rear one. Either way, that doesn't explain why yours gets so hot so quick. Second, 1100 deg EGT is way too hot for just running down the road with no huge load. That should be near the max with a heavy load. Normally you'd expect somewhere in the 600-800 deg range. Also, why such high RPM at 62 MPH. Are you running a super low gear ratio rear end. At that speed most try to hit around 1800 RPM. Your fuel economy is going to be horrible running that high RPM at normal cruise speed. By the way, normal thermostats for the 4bt/6bt are set at 83 deg C or 180 deg F.
My air/water intercooler is not the best because it uses radiator water. I think the load is just the brick shape. Lol. I’m kind of stuck with the rpms because of three speed trans and 4.88 gears. My mpg is about 14 which I’m ok with. If the stock thermostat is 180, that’s what I have.

By pull and leave the thermostat are you meaning to leave it out? You have to have one in there to block the bypass when hot.
170 is way too low for a normal operating thermostat. Check the temperature at the outlet on the head and either side of the thermostat when it running hot.
Yes, I was going to leave it out. I don’t follow you on “block the bypass when it’s hot”. My thermostat is just like a car one. It doesn’t block anything when it’s hot. It opens. Do they have reverse ones?
 

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Don't leave the thermostat out. It's needed to control flow and help cooling. Is there a weep hole in the thermostat. Is there a possibility there's a air bubble or pocket in there. Is there a wire spring in the lower hose to keep it from collapsing which would limit coolant flow.

On the radiator you need to create a low pressure area on the outlet side for air to flow thru. Do you have an overflow bottle on this to keep the system full.
 

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OK, wrong thermostat. These have to have the bypass valve on them. The valve will either be a flat plate or the later ones have a tapered plug on them. With out the valve hot water just recirculates in the block without being directed to the radiator. There was a change in there somewhere that required some grinding of the thermostat housing to prevent interference.
 

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Discussion Starter · #9 ·
Don't leave the thermostat out. It's needed to control flow and help cooling. Is there a weep hole in the thermostat. Is there a possibility there's a air bubble or pocket in there. Is there a wire spring in the lower house to keep it from collapsing which would limit coolant flow.

On the radiator you need to create a low pressure area on the outlet side for air to flow thru. Do you have an overflow bottle on this to keep the system full.
On a standard thermostat, it is needed to control flow and help warm up. It has no way to help cooling except to open. In extreme cold, it could close again or partially close to help keep the engine warm. I’m in Florida and warm up is not the problem. (Maybe come winter I would want it) I don’t recall about the weep hole, but I believe I bought a stock thermostat for a 6BT. Are they different for a 4BT?

As far as your other questions. Yes, there could be an air pocket. How would I know. My lower (and upper) hoses are actually stainless pipes, so no springs. The fans are on the outlet side of the radiator creating the low pressure. I do have an overflow and I’m not losing any coolent.

OK, wrong thermostat. These have to have the bypass valve on them. The valve will either be a flat plate or the later ones have a tapered plug on them. With out the valve hot water just recirculates in the block without being directed to the radiator. There was a change in there somewhere that required some grinding of the thermostat housing to prevent interference.
Im completely in the dark on this. I replaced the thermostat many years ago when I began building this truck. I don’t recall anything special about it. Please enlighten me. When you say “without the valve, water just recirculates”, isn’t that what all thermostats do? I definitely did not grind my housing.
 

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I suggest you have a good read of the cooling section in the manual.
These engines have a built in bypass to speed engine warm up and require a proper function thermostat to operate correctly.
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This is the article on the housing grinding if needed, also has good pic's of the 2 styles of proper thermostats
 
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Discussion Starter · #12 ·
Very interesting. I wonder if I have the wrong thermostat. Is there a part number for the correct one? Is the thermostat the same for a 4BT and 6BT? I am very concerned about this. My memory is foggy, but I sure don’t recall anything fancy about the thermostat. I surly didn’t grind anything. I’m going to dig through my old parts and see if I have the old stat.

Thankyou Blackduck. I will buy you a drink. Hell, I’ll buy you lunch and a drink.
 

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What is the serial number of your engine? I'll look up the part number for you. If it is a CPL 0857 the OEM thermostat is Cummins part 3283589 which was replaced by 3972071 which has been replaced by 5292738. If you have the water/air aftercooler, there should be a bleeder valve on that unit to get air pockets out. See part #1 in the diagram below.
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On a standard thermostat, it is needed to control flow and help warm up. It has no way to help cooling except to open.

As far as your other questions. Yes, there could be an air pocket. How would I know. My lower (and upper) hoses are actually stainless pipes, so no springs. The fans are on the outlet side of the radiator creating the low pressure. I do have an overflow and I’m not losing any coolant.
so to answer on helping cooling, if there isn't a thermostat then the water doesn't have the time for the radiator to remove the heat. you can end up with a temp that wont quit climbing.

usually on the water outlet there is a bleed valve or you can just remove the plug to get the air out of the engine as long as the radiator is above the top of the engine.

as for a low pressure area the fans alone wont create that, there needs to be something to block the air from flowing over the fans exit to allow the air to get thru.
 

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Discussion Starter · #16 ·
so to answer on helping cooling, if there isn't a thermostat then the water doesn't have the time for the radiator to remove the heat. you can end up with a temp that wont quit climbing.

usually on the water outlet there is a bleed valve or you can just remove the plug to get the air out of the engine as long as the radiator is above the top of the engine.

as for a low pressure area the fans alone wont create that, there needs to be something to block the air from flowing over the fans exit to allow the air to get thru.
Water going to fast through a radiator not removing heat is a myth. It’s been proven false many times. What people confuse is heat transfer per gallon. Example….

1. You have 1 gallon go through your rad per minute and it removes 20 degrees of heat, you would have 20 degrees of heat per minute is removed.

2. Now, let’s say you have ten gallons go through your rad per minute. But because it’s going through so fast, it can only remove 2 degrees of heat per gallon. Yes, the per gallon amount is much less, but the total heat removed is the same. 10 gallons x 2 degrees per minute = 20 degrees per minute.

In reality, it’s more likly that the second example will remove 3 or 4 degrees per gallon per minute giving you a much better cooling because heat transfer is better the greater the differential. So by the time the water has cooled 15 degrees, it cools slower for the last 5.

Now what Blackduck is referring to is no myth. The Cummins has a special thermostat that shuts a bypass off. Most thermostats don’t work like that.

I will look for a plug. My radiator is about level with the engine. Do you think I can just park on a steep slant?

Don’t follow your last paragraph. Block the air from flowing over the fans? Are you referring to a shroud? I do have a very tight shroud.
 

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Cummins is not unique using a bypass thermostat, it is very common.
Not buying into the coolant moving too fast with out one but there are definitely issues.
Thermostat openings are made to suit he engine they are used in 1) to hold some pressure in the block to help reduce cavitation and 2) to reduce thermal shock of hot/cold cycles of coolant coming from the radiator.
To control thermal shock some engines now have the thermostat on the inlet from the radiator. Can be sods of things to change as they are buried low on the engine. ( IE; Holden (Chevy) Cruise Diesel)
 

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Discussion Starter · #18 ·
Something is off somewhere. 230 deg is super hot. The rear position on the head is the hottest point on the engine. Usually, the temp sensor was in the front top point near the thermostat and the cooling fan sensor was in the rear one.…….
I was re reading the thread and got to thinking about this statement. If the rear of the head is the hottest point and Cummins suggests the temp sender in the front, wouldn’t the rear be hotter than what your gauge says?

For example, a gauge that has a sensor in the front reads 190 and the same gauge with a sensor in the rear would read 230. Is it possible that my truck is running just fine? I guess I could move my sensor to the front location for a test. I keep coming back to the issue that my truck runs fine and I don’t lose any water. Maybe I’m trying to fix something that isn’t broke.
 

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I see the sensor in the rear position reading +30* from when my thermostat opens the FIRST time and +20* once everything is up to temp so that is the difference between the front and rear of the head.
 

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Discussion Starter · #20 ·
I see the sensor in the rear position reading +30* from when my thermostat opens the FIRST time and +20* once everything is up to temp so that is the difference between the front and rear of the head.
So what does your truck run at.

Today, I idled the truck to the thermostat opened. I had a temp gun and was checking all kinds of stuff. I noticed that my gauge reads about 10 degrees higher than the head or even the back side of the sensor. Do you think the water inside there is ten degrees hotter than the steel?
 
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