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Engine swapped cooling system question

Old 11-05-2018, 10:57 PM
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Hello all,
I am new to this forum and joined to get yalls opinion on a project I have going on. For my work I am installing a LM7 (I k ow itís not a LSX but the title of this thread lead me to believe this is the right place I need to be) with a th400 into a 1945 Mack fire truck. My question involves the cooling system.
The OEM truck water pump, tensioner, and crank pulley have been replaced with those for a 2005 GTO. I finally got to start the engine and get it up to operating temp but I noticed the lower radiator hose stayed cold and the upper hose was hot going into the radiator. It is a new t-stat from Oreillys that is supposedly a 187*. The lower hose finally started heating up after engine temp got over 200*. Iím thinking t-stat is sticking but Iím second guessing myself because it is a new t-stat and a unique cooling situation. I have a new 160* t-stat on order to see what that does. Is it possible that the engine to radiator height is affecting flow? The rad cap is 10 lbs as recommended by the radiator repair shop (original 1945 radiator re-cored). I saw where there is a debate as to coolant flow direction on LS bases engines but I swear mine is sucking from upper hose. Is there an issue with LS water pump on a LM engine? Please let me know yalls thoughts. Something g just doesnít seem right to me but I canít put my finger on it.

Last edited by Monkiejohnson; 11-05-2018 at 11:07 PM.
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Old 11-05-2018, 11:01 PM
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Iím trying to post pics but having trouble
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Old 11-05-2018, 11:06 PM
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Water pumps on LS engines are interchangeable. That thermostat might have stuck. New ones can be bad, it happens. LS flow IS out the top of the water pump, and in thru the bottom thru the thermostat. That is what's different; where the T-stat is. The lower hose stayed cool until the hot water went thru the radiator after the T-stat opened and let water in thru the bottom. Sounds like it's working normally now though. There is no debate among knowledgeable people about LS water flow.
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Old 11-05-2018, 11:11 PM
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Do you think the height of the upper tank has any effect on the system? Straining the pump or other issues?
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Old 11-05-2018, 11:19 PM
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The engine doesn't care where or how high - within reason - the radiator is as long as there are no air pockets.
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Old 11-05-2018, 11:58 PM
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That is a cool truck! Could you put more pics of it here?
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Old 11-06-2018, 02:01 AM
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sounds like trapped air. either fill the block thru the waterpump outlet (top) or get a vacuum filler kit
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Old 11-06-2018, 06:10 AM
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Sounds like trapped air to me as well but man, you should have no trouble filling that unit. You have a good rake on the motor and the rad fill is well above the top of the motor. No need to fill through the hose like normally is a good idea, that rad should have a straight shot to the cap.

The upper hose is probably getting hot because heat naturally rises.

Check to make sure the radiator is full than let it run a bit next time. Just keep the temp gauge below 220

You will have to post some pics of the car when done. Looks like fun
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Old 11-06-2018, 04:15 PM
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pAn air pocket crossed my mind as well but then I second guessed myself because I thought for sure with the height different I shouldnít have any problems purging the system. I know also that the OE system pressure is around 15-16 where this one is only 10 due to original radiator tanks so I donít know how that with affect the system. With cooling fan running temp was 197 before upper hose blew. Here are some more pics.

Last edited by Monkiejohnson; 11-06-2018 at 04:34 PM.
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Old 11-06-2018, 05:13 PM
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How cool is that!

A higher pressure cap means it will go a few degrees hotter before it boils. I say run it, watch the gauge and shake it out.
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Old 11-06-2018, 07:16 PM
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Iíve got a 175 and a 160 t-stat standing by in case it starts to run to hot with the 10 lb cap.
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Old 11-07-2018, 07:58 AM
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Very cool fire truck!

The thermostat temp only changes what temperature the thermostat opens. Contrary to popular belief thermostat opening temperature has zero to do with a vehicle overheating. As Pop N Wood said the radiator cap pressure only changes the boiling point of the coolant.
  • Overheating is due to a poorly designed or poor performing cooling system.
  • Engine operating temperature is due to the thermostat opening temperature on a properly functioning cooling system.
Factory thermostat is 195 and honestly below that you start to run into emissions issues based on fueling with the factory PCM. Running an aftermarket system could change that a bit due to programming but there is still a sweet spot for a driven (non race) vehicle. Even still for a street driven vehicle you will need to be concerned with burning contaminants (condensation, etc.) out of the oil when driving or your oil life and engine wear will suffer.

My suggestion: keep the suggested radiator cap or consider damaging the radiator (weakest link) and keep the factory thermostat.

Make a good fan shroud and run a good, high quality (preferably electric) fan that pulls a lot of CFM through the radiator (not a pusher). From your first picture it looks like that bit is taken care of. Run the fan from the PCM, set the on temperature around 205į (5 to 10į above the stat opening temp) and Bob's your uncle.
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Old 11-07-2018, 10:38 AM
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Originally Posted by Monkiejohnson View Post

Here's your problem. I have found antifreeze to be very ineffective on the garage floor, needs to be in the engine and radiator.

On a serious note, it does sound like you just still have air in the system. Also, for what its worth, I would refrain from using Dexcool. It works fine in applications its designed for, but in a swap with a non sealed cooling system it makes a mess. Whenever Dexcool and air mix, they form a mud like solution, so if you have an overflow hose on the radiator whenever the radiator cools down and pulls fresh air back in to the system you get that mud mess around it. I switched to the old green antifreeze and never had a problem again.
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Old 11-07-2018, 11:51 AM
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i thought that was tranny juice
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Old 11-07-2018, 01:35 PM
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Iíll look into a different antifreeze. Supposedly our universal is good for application but I will double check. The engine never really overheated (engine temp never even went above 210) I was just concerned about the amount of time it took for the t-stat to open and the temp difference in the hoses. The upper rad hose blowing off could have just been me not tightening it down enough or the fact that the original neck doesnít have a lip on it. System pressure is where my main concern is because the rad tanks and necks are original 1945 and I am concerned about rupturing them with to high of pressure. My thought is keep an operating temp of around 180 or so should keep pressure down.
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Old 11-07-2018, 06:30 PM
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With only a 10lb cap, I would not be using the stock stat, or trying to run the engine anywhere near 200degF.

As Monkie says, you'd want to get things down to say 180 or so. Ensure that fan is properly shrouded and pulls air through as much of the core as possible. And with the colder stat..make sure your fan will turn off/on at a suitable temperature too
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Old 11-07-2018, 08:31 PM
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Originally Posted by Monkiejohnson View Post
I do not see in your picture much of an outward bead in the radiator upper neck. If it doesn't have one, add one before going further.

Also, if the radiator was recently re-cored, I suspect it is capable of running 16psi without issue. With regard to thermostats, I run stock 195 stuff, and ambient here gets over 120. You aren't helping the engine with even a 180, and the stat just sets min. operating temp.

Cool project, and thank you for sharing pictures.
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Old 11-07-2018, 09:22 PM
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If a bead isn't possible, try to weld or braze some "nubs" around that upper neck to help retain that upper hose. It will go a long ways to keeping your cooling system healthy longer!
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Old 11-08-2018, 09:31 AM
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Originally Posted by ls1nova71 View Post
Here's your problem. I have found antifreeze to be very ineffective on the garage floor, needs to be in the engine and radiator.

On a serious note, it does sound like you just still have air in the system. Also, for what its worth, I would refrain from using Dexcool. It works fine in applications its designed for, but in a swap with a non sealed cooling system it makes a mess. Whenever Dexcool and air mix, they form a mud like solution, so if you have an overflow hose on the radiator whenever the radiator cools down and pulls fresh air back in to the system you get that mud mess around it. I switched to the old green antifreeze and never had a problem again.
you saved me alot some typing......^^^ this is truth, learned the hard way. all of my new cooling system looked like muddy pond water, and the staining is very hard to get cleaned back out of system
very cool truck.
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Old 11-08-2018, 01:12 PM
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That motor needs to be burped. The steam line into your water pump is correct (I suspect you already knew this) in relation to where it exits and that is good. There is a spill free funnel system that will help burp your cooling system (google it or email me), it takes about an hour running time to get all the trapped air out of the system or you can simply keep recycling the system by bringing it to operating temp., cooling down, relieving pressure and refilling. I'm curious of what work you had done on the radiator, flushed, re-cored? I would also check for the thermostats operation by putting it in a pan of water while using a thermometer to observe it opening and closing. As someone already stated, new t-stats have been known to not operate correctly, this is one way to be sure the t-stat is working correctly. With all this said I highly suspect that engine just needs a good burping. Being a retired fireman I really like your build, nice ride.
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