Just double checked using thermal, on top of radiator inlet it's actually about 109C (228F) and bottom radiator outlet is 70C (158F)... Wtf? I am still going to do the flush and see, but is there anything else or is this really considered normal?? If normal, I want to see something from manufacture stating that.

I should add I took those readings while "burping" the system, funnel fitted at the radiator and vehicle inclined. Heater on full.


Hard to see, but this is taken from the bottom of the truck where the lower radiator hose meets the radiator. Aiming right at the outlet, understand plastic is a poor conductor, but we're measuring apples to apples (bottom radiator vs. top radiator) not the actual temp of coolant inside.

Taken from the top, right where the upper hose meets the radiator inlet. Again, not interested in actual temp, just interested in temp difference between top and lower radiator to determine if it's actually cooling the fluid.

As a side note, don't mind the color difference between the two photos. Bottom looks hotter because it's brighter, it just looks that way in reference to surrounding items within the picture frame. Same goes for the top photo. Without temperature reference you'd assume bottom is hotter, but that's not the case.


@Doc Olds I know you mentioned this is normal for H3 in several threads/many threads, do you have any source? I want to believe you and just keep driving without worry, but there's conflicting information I am reading from other H3 owners. With all due respect of course, your thoughts and opinions are greatly appreciated 🙏

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You're doing great with the radiator cooling. Your fluid is not getting into the radiator. It's a bottom thermostat problem. Transfer to the top and you will forget about this problem forever.

 

I've removed the thermostat so there's nothing stopping fluid from getting into the engine. Why I am absolutely stumped, I am searching the web up and down trying to find something from GM on this matter.

 

You Radiator is working like it should. The volume of coolant is a conductor, it can transfer heat by conduction just like anything else, even against the flow of coolant direction. Once up to full operating temp, you would expect your observations of appx Radiator temps Top vs Bottom. You have cooling transfer going on, and a pretty healthy buffer at that.

The internet is a source of info and BS, some info, some good info and some good BS based upon opinion based and mere anecdotal observations. Example, just because your dog chits on the rug by the front door does not mean mine or everybody's dog chits on the front door rug.

My source is 15 years in the performance parts industry (GM Trucks), having read all the TSBs issued by GM regarding the H3/H3Ts, as well as having worked on some 50+ H3s and H3Ts. I don't do repairs on other people's trucks, I help them with mods if they ask when I can. You can go to the NTSB web site and search TSBs or other bulletins issued for any vehicles based upon customer driven complaints/concerns and look those relating to cooling/engine up if you want. When these trucks were being made and sold Dealerships got a bunch of customers whining about the temp gauge readings .... OMG passed half way.... my last car didn't do that...... it must be overheating....etc... The GM response and what I have seen is what I base my 3/4 is normal on. In general, the first point made to the dealer techs is scan for actual temp and inspect the cooling system for dirt, debris or compromise, and coolant level and quality. If all is good, then send them on their way. If they repeat whine a couple more times, change the instrument cluster, then send them on their way with zero actual cooling system work.

You live in a HOT climate, this year is hotter than many. Your temp is going to be higher than mine and probably by appx the difference in compared outside ambient temp.

Good luck.

 

Coolant passages are a series of channels or cavities that allow coolant to circulate through the engine. These passages are typically located in the cylinder head, engine block, and sometimes in other engine components such as the intake manifold or exhaust manifold. In the cylinder head, coolant passages are specifically designed to help regulate the temperature of the engine by circulating coolant around the combustion chambers and valve seats.

The coolant passages in the cylinder head are typically made up of small channels and passages that are machined into the metal. The size, shape, and location of these passages can vary depending on the specific engine design. For example, some engines may have passages that are larger or more complex than others, depending on the size and configuration of the combustion chambers.

The primary purpose of the coolant passages in the cylinder head is to transfer heat away from the combustion chambers and other hot spots in the engine. When the engine is running, the combustion process generates a lot of heat, which can cause the metal to expand and warp if not properly cooled. The coolant passages help to regulate the temperature of the engine by circulating coolant through the passages and carrying away the excess heat.

In addition to regulating engine temperature, the coolant passages in the cylinder head also help to prevent overheating. Overheating can occur when the engine is running too hot for an extended period of time, causing damage to engine components such as the cylinder head gasket, valves, and pistons. The coolant passages help to prevent overheating by maintaining a consistent and optimal operating temperature for the engine.

If the coolant passages in the cylinder head become clogged or damaged, it can lead to engine overheating and other serious problems. Clogs can occur due to a buildup of mineral deposits or other debris, which can prevent the coolant from flowing through the passages. Damage can also occur due to corrosion or physical damage to the cylinder head.

To prevent issues with the coolant passages in the cylinder head, it’s important to maintain proper engine coolant levels and perform regular maintenance on the engine. This may include flushing the coolant system, replacing damaged or worn components, and checking for signs of leaks or damage.

In conclusion, the coolant passages in the cylinder head play an important role in regulating engine temperature and preventing overheating. These passages are designed to circulate coolant around the combustion chambers and other hot spots in the engine, carrying away excess heat and maintaining a consistent operating temperature. Proper maintenance and care of the coolant passages can help to prevent engine damage and prolong the life of the engine.

As mentioned in the previous section, the primary purpose of coolant passages in the cylinder head is to transfer heat away from the combustion chambers and other hot spots in the engine. This is accomplished through a process called convective heat transfer, which relies on the flow of coolant through the passages to carry heat away from the engine.

When the engine is running, coolant is circulated through the engine block and up into the cylinder head. The coolant enters the cylinder head through a port on one end and flows through the passages, carrying away heat as it goes. The coolant then exits the cylinder head through another port on the opposite end and returns to the radiator to be cooled down before being recirculated back through the engine.

The size, shape, and location of the coolant passages can have a significant impact on how effectively heat is transferred away from the engine. For example, larger passages can allow for greater coolant flow, which can help to dissipate heat more quickly. However, larger passages can also result in a loss of pressure, which can impact the effectiveness of the coolant system as a whole.

Another factor that can impact the effectiveness of coolant passages in the cylinder head is the material that the passages are made from. Different materials have different thermal conductivity properties, which can impact how effectively they transfer heat away from the engine. For example, aluminum is a common material used in cylinder heads due to its high thermal conductivity, which allows it to transfer heat away from the engine more efficiently.

In addition to these factors, there are several other things that can impact the effectiveness of coolant passages in the cylinder head. For example, if the engine is running at a high temperature for an extended period of time, it can cause mineral deposits to build up inside the passages. This can restrict coolant flow and reduce the effectiveness of the cooling system.

Leaks in the coolant system can also impact the effectiveness of the passages, as coolant may not be able to circulate properly through the engine. In some cases, leaks can also result in air getting into the cooling system, which can cause hot spots to form in the engine and lead to overheating.

Overall, the coolant passages in the cylinder head play a critical role in regulating engine temperature and preventing overheating. To ensure that these passages are functioning properly, it’s important to maintain proper engine coolant levels, perform regular maintenance on the engine, and address any issues with the cooling system promptly. By doing so, you can help to prolong the life of your engine and avoid costly repairs down the road.

Advantages of Cylinder Head Coolant Passages:

1. Improved Engine Performance: The primary advantage of having coolant passages in the cylinder head is that they help to regulate the temperature of the engine. By carrying away excess heat generated during the combustion process, the coolant passages help to prevent the engine from overheating, which can cause damage to engine components and reduce overall performance.
2. Increased Engine Longevity: Overheating is one of the most common causes of engine failure. By regulating engine temperature and preventing overheating, coolant passages in the cylinder head can help to prolong the life of the engine and reduce the likelihood of costly repairs.
3. Better Fuel Efficiency: When an engine is running at the optimal temperature, it is able to burn fuel more efficiently, resulting in better fuel economy. By helping to maintain a consistent and optimal operating temperature, coolant passages in the cylinder head can contribute to better fuel efficiency.

Disadvantages of Cylinder Head Coolant Passages:

1. Risk of Clogs: Over time, mineral deposits and other debris can build up in the coolant passages, which can restrict coolant flow and reduce the effectiveness of the cooling system. This can lead to engine overheating and other serious problems.
2. Corrosion and Physical Damage: Coolant passages in the cylinder head can also be damaged due to corrosion or physical damage to the cylinder head. This can lead to leaks and other issues that can impact engine performance and longevity.
3. Design Complexity: The design and construction of coolant passages in the cylinder head can be complex, requiring precise machining and materials selection. This can increase the cost and complexity of engine manufacturing and repair.
4. Risk of Leaks: Coolant passages in the cylinder head are susceptible to leaks, which can cause the engine to lose coolant and overheat. Leaks can be caused by a variety of factors, including corrosion, physical damage, and faulty gaskets or seals.

In summary, while coolant passages in the cylinder head provide numerous benefits, they also come with certain disadvantages. To ensure that coolant passages function properly and avoid potential issues, it’s important to maintain proper engine coolant levels, perform regular maintenance on the engine, and address any issues with the cooling system promptly.

 

That's respectable. I searched NTHSA* website and found some TSBs for H3's but not much in relation to cooling, specifically temperature ranges as we're discussing here. Idiot gauge aside, I don't care what mine reads I am going off what my scanner is showing me (220F-238F). Only text I can find is the overheating troubleshoot guide and that has temperature of 225F as the overheating baseline, it asks "does the coolant temp exceed 225F on the scanner, yes or no?" if yes proceed to next step. Owner/Repair Manual doesn't show much either expect an illustration with the gauge at 3/4 mark with no context or text. If you can link me to a TSB that addresses this I would greatly appreciate it, not that I don't trust your word I just have to see it for myself for the piece of mind.

@hummerz thanks for the write up on how cooling works. Understand the engine coolant passages etc. I hope my case is not as severe. Given that coolant is actually flowing through the radiator, I am assuming if there was a restriction or blockage we'd see less flow and possibly higher pressure?

 

as I said before, the I5 has a stupid cooling system. in your case, there are only two options left - a faulty sensor or a pump. I'm leaning more towards the pump. in this engine, the inlet and outlet of the coolant is implemented on the first cylinder. if the pump is weak, then the cooling of the fifth cylinder will be poor. and on the fifth cylinder is a temperature sensor.

 

I just replaced the water pump yesterday and added weather stripping on top between radiator and AC condenser coil. Today I went and bought a rubber mat from Home Depot, cut to size and installed it below the radiator, tucked it back behind the skid plate - see photos below.


Some weather stripping on top sealing the gap between radiator and AC condenser coil.

Rubber mat from Home Depot. I actually end up cutting the front a bit and tucking it behind the radiator. There were already pre drilled tapped holes that I was able to attach to.
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Went for a test drive and to my surprise it's actually running cooler. Still warm but an improvement overall, only got to 220F briefly on a highway but once on the street 207-208F, got to 215F going up a hill but cooled off once leveled.

I think what might have been happening is the hot engine air was getting drawn in from below and maybe some over the top. I am gonna take the bumper off and do some work up front to better isolate the radiator and redirect air. I think all those baffles, diffusers, seals, etc. play an important role herre, air flow is critical for proper heat transfer. Removing those baffles/diffusers may not make a difference in some driving situations, but when it's 100F + outside and conditions are extreme, every little detail counts. I was surprised seeing my temperatures drop while sitting at the light, before it would just keep rising. One other thing to note, my Intake Air Temp was 130-140F not sure if that's an indication of anything.

I am going to keep tinkering with it and do more test drives tomorrow to be sure. I take the same route every time and note where I start to notice heat increase. Ambient temperature was 106F this time around, I'll check again tomorrow when it's 112F and sun out.

 

Update: took another test drive 111F outside AC full blast. I can definitely say engine is running cooler especially when stopped or city driving, getting 205-208F. However once the transmission temp start to creep up to 235F engine will stay between 215-217F and gets worse on the highway. I'll get 220-221 on the highway traveling about 65mpg and RPM below 2k so the fan is not really doing much. Once I am off the highway, city driving, accelerating and hearing the fan going brings the temps down. Transmission seems to stay pinned at 235F.

I think the added seal on top and skirt on the bottom helps during idle, but at highway speeds I suspect the missing baffles/diffusers is not allowing adequate airflow through the grill and radiator. I believe the baffle as mentioned earlier in this thread is used to produce high/low pressure environment (Bernoulli's principle) which helps with airflow within the cavity between the grill/pumper and radiator. @hummerz you mentioned that air no longer goes through the grill in modern cars but rather over the grill due to EPA? Correction: you said most of the air will not go through the grill because of EPA, therefore it's best to seal air intake (I think you meant as in air going into the grill, not the actual air intake) on all 4 sides. Sorry, had to re-read what you said.

 

I get a huge drop in temp when increasing rpms, therefore my engine passages are clean!