Radiator too large, tstat too high?

[Matt_G]

Without question the radiator is more than I need right now, but is my 195*F tstat too high for it?
1998 C1500 5.0L Vtech
Radiator was 29x18x1", upgraded to 34x18x2" 3 core with trans cooler unused and plugged.
Clutch fan was ditched for electric fans that rarely ever need to run at idle.

As the cooler weather starts to set in, I'm running into issues with the radiator becoming over-pressurized and blowing by the radiator cap (like it's supposed to when over-pressurized). Engine temps are ~180*F and steady at operating temp per dash and ECM readings.
Water pump, Tstat, radiator cap, dash Tmon and ECM Tmon was replaced when I put in the radiator two months ago. System is full of fluid but has been draining the reservoir tank since the weather has turned cooler in the 30-40's at about a rate of 1 tank per month, driven daily to work.

I'm thinking the Tstat doesn't reach temp because the residual flow from the radiator (and Tstat pinhole) keeps cooling it too much, or when it does open it introduces a lot of much cooler radiator flow and the Tstat doesn't recover/warm up soon enough before the internal loop surpasses temp? The radiator return hose headed to the block is only warm enough to not want to keep your hand on it for long.



All of that out of the way, my question is..
Would the system benefit from a lower temp Tstat or would that risk shocking the system more regularly? At some point, I'm concerned about dramatic temp change on the block, or continuous temp differences across the block causing warp if I did get a lower temp Tstat. I don't know a great deal about how those concerns are factored in to know if they are an issue or not, but it has crossed my mind.

Thanks.

 

[CumminsFever]

It really sounds like a head gasket issue. Radiator upsizing shouldn't cause the issues you're experiencing, and in fact, even a non-functional thermostat won't do this. Compression/air in the cooling system could or would do this.

 

[RichLo]

First of all, No and No... You cant have a radiator too big and a 195 T-stat is a factory temp.

Second, you have other problems, possibly like Cummins' said. Its a closed loop system that doesn't puke unless something is wrong. The overflow tank is just that, an overflow reservoir for thermal expansion/contraction of the fluid. It should never puke out coolant onto the ground (PETA and EPA stopped that in the 1960's)

If you are constantly having to add coolant then it is either consuming it or leaking it. If you notice the overflow is puking then you are either boiling it or over-pressurizing it from a blown head gasket. You can boil it due to having straight water (rusty passages), or a faulty t-stat, or cracked head or block, or clogged radiator, etc

Its time for more diagnostics, this will help you...

https://www.amazon.com/gp/aw/d/B08BG3WTDX/?_encoding=UTF8&pd_rd_plhdr=t&aaxitk=8d1f2c39f6a5aa11a9fa6d7b4b699ada&hsa_cr_id=2486550630801&qid=1700968972&sr=1-2-9e67e56a-6f64-441f-a281-df67fc737124&ref_=sbx_be_s_sparkle_mcd_asin_1_title&pd_rd_w=YrHji&content-id=amzn1.sym.417820b0-80f2-4084-adb3-fb612550f30b%3Aamzn1.sym.417820b0-80f2-4084-adb3-fb612550f30b&pf_rd_p=417820b0-80f2-4084-adb3-fb612550f30b&pf_rd_r=1NRFSK13ASBGG12WJ95T&pd_rd_wg=DaQDF&pd_rd_r=239f7f0a-aa11-4a60-b768-47696378abc9&th=1

 

[454cid]

X3, you've got something else going on. Get a loaner cooling system tester from the auto parts store and pressurize the system, and look for leaks. Also look for pressure drop. A thermostat that stays partially open will make for a slow warm up, and may not let the engine come up to full temperature at all. It won't over pressurize anything, However. How do you know the pressure is too high... overflow bottle filling up? Yet, you say it's draining the overflow bottle.

 

[Matt_G]

X3, you've got something else going on. Get a loaner cooling system tester from the auto parts store and pressurize the system, and look for leaks. Also look for pressure drop. A thermostat that stays partially open will make for a slow warm up, and may not let the engine come up to full temperature at all. It won't over pressurize anything, However. How do you know the pressure is too high... overflow bottle filling up? Yet, you say it's draining the overflow bottle.

It's blowing coolant out of the radiator cap. I can hear it leaking by and there's coolant left over on the battery and front grill by the time I get home. No noticeable steam or anything. My thoughts were that it was boiling the internal loop, pressurizing the rest of the system and exhausting at the radiator cap. Only reason it should leak at the cap is if it exceeds 15psi I believe.

I'll try a new radiator cap and grab a loaner cooling system test kit from the parts store tomorrow just to be certain.

Will update late tomorrow if I can.

 

[454cid]

It's blowing coolant out of the radiator cap. I can hear it leaking by and there's coolant left over on the battery and front grill by the time I get home. No noticeable steam or anything. My thoughts were that it was boiling the internal loop, pressurizing the rest of the system and exhausting at the radiator cap. Only reason it should leak at the cap is if it exceeds 15psi I believe.

I'll try a new radiator cap and grab a loaner cooling system test kit from the parts store tomorrow just to be certain.

Will update late tomorrow if I can.

If the pressure exceeds the cap rating, the coolant should be exiting the area through the overflow hose, filling the coolant bottle. If you're getting coolant coming out at the cap outside of the hose, you have a bad cap or some other leak. How's the 5/8th inch diameter connection on the back side of the tank, that's probably unused on your truck? Big Blocks return the coolant from the heater core there, but I belive small block Vortec engines, do not. Typically aftermarket radiators include a rubber plug to block it off.

 

[Komet]

Check for combustion gases in the coolant. It sounds like you're trading exhaust and coolant in the combustion chamber (i.e. head gasket failure). Is it smoking sweet white smoke ever?

 

[GoToGuy]

The radiator has two functions. 1 to provide a closed pressure limited cooling system. 2 the excess thermal expansion is relieved into the white expansion holding tank, and returned when cooling.. 3 coolant traces around cap and neck , radiator damage or the cap neck or cap/ cap seals are damaged. Inspect , test , replace parts as needed.
If it was really making pressure in coolant system why didn't it fill the overflow tank.? Combustion gases are super heated, cooling system would have high temp.
Cap has two sealing areas to contain coolant. Within cooling system. If you have coolant anywhere else, you have a leak.
Are you guessing you have bad head gasket?
Are you guessing that the cap is blowing pressure out ?
A dynamic compression check for low cylinder, ( possible head gasket breach )
A differential compression check to identify what is wrong with a suspect low cylinder.
It's " ok , there's fluid coming from somewhere hmm, cap, neck , loose hose clamp, so forth"
Don't jump on the bad head gasket instantly, unless you got steam spouting out of the head, then yeah, ok.
When things happen right after service, it's always a " cover your bases " good idea, re check your work. It's easy to slip hose on , slip clamp in place, ( place some kind of interrupt here ) then it's , ahhh where's all that coolant coming from?

I was doing an oil and filter on girlfriends car. Friends over beer and gabbing. Poured 4 quarts in . Whatzat! Brown ooze ? Yep, got distracted by the G cups, blanked the oil drain plug. It only takes 1 time.....

 

[Erik the Awful]

Without question the radiator is more than I need right now, but is my 195*F tstat too high for it?
1998 C1500 5.0L Vtech
Radiator was 29x18x1", upgraded to 34x18x2" 3 core with trans cooler unused and plugged.
Clutch fan was ditched for electric fans that rarely ever need to run at idle.

As the cooler weather starts to set in, I'm running into issues with the radiator becoming over-pressurized and blowing by the radiator cap (like it's supposed to when over-pressurized). Engine temps are ~180*F and steady at operating temp per dash and ECM readings.
Water pump, Tstat, radiator cap, dash Tmon and ECM Tmon was replaced when I put in the radiator two months ago. System is full of fluid but has been draining the reservoir tank since the weather has turned cooler in the 30-40's at about a rate of 1 tank per month, driven daily to work.

I'm thinking the Tstat doesn't reach temp because the residual flow from the radiator (and Tstat pinhole) keeps cooling it too much, or when it does open it introduces a lot of much cooler radiator flow and the Tstat doesn't recover/warm up soon enough before the internal loop surpasses temp? The radiator return hose headed to the block is only warm enough to not want to keep your hand on it for long.



All of that out of the way, my question is..
Would the system benefit from a lower temp Tstat or would that risk shocking the system more regularly? At some point, I'm concerned about dramatic temp change on the block, or continuous temp differences across the block causing warp if I did get a lower temp Tstat. I don't know a great deal about how those concerns are factored in to know if they are an issue or not, but it has crossed my mind.

Thanks.

I'll try a new radiator cap

Don't buy any parts until you troubleshoot what's actually wrong. Fire it up and watch down the radiator neck. Is it blowing bubbles? I'll bet it is. It's a Vortec, so there are equal chances it's a headgasket or a cracked head. There's also a chance of a cracked block if it's every been seriously overheated.

BUT! Diagnose first.

You're in Oklahoma. There's no such thing as "too big" of a radiator.

 

[Matt_G]

Update

Drove truck into town to get the leak test kit this morning.
White smoke startup @ 34*F, clean exhaust sometime before engine temp hit 180*F. Smells normal, no sweetness before and after warmup.

Radiator cap had leaked at cap seal by the time I got home per usual, wasn't actively leaking when I checked but the neck and everything around it is wet with coolant.
I Let the truck cool for a few hours and then attempted radiator leak test once block and radiator cold to touch, test failed. Discovered or created radiator leak on driver side at plastic/aluminum seam @ ~15PSI.
I also attempted leak test on the radiator cap, broke seal near rated 16PSI and resealed at 11PSI.

Took the tool back into town and tested 3+ new radiator caps of various brands, same behavior. Radiator cap in place is good for PSI rating.


I don't earnestly believe the leak at the radiator seam existed previously, it starts to leak fluid noticably in a constant pouring stream before 10PSI now and the radiator cap appears to be good for up to 16PSI as rated, yet had still leaked before I got home at some point. Maybe the tool is out of calibration and I inadvertently pushed it to ~20PSI? The radiator cap tests lead me to believe otherwise..

So for now, the leak test is a dud bust until I can get the new radiator tested and ruled out. Parts store has it in stock and will warranty the newer one I bought and installed in October. I'll put it in over the next day or two.

How's the 5/8th inch diameter connection on the back side of the tank, that's probably unused on your truck? Big Blocks return the coolant from the heater core there, but I belive small block Vortec engines, do not. Typically aftermarket radiators include a rubber plug to block it off.

It's blocked off.

I'll note that the plastic clip on the reservoir return line above the cap seal is a tad loose, I can pull, push and twist it on the stem until it hits the swell. I'll swap this for a screw-type clamp. I don't believe it's the issue though, line is free of debrise and kinks. Shouldn't have any back-pressure resistance to push that much fluid out from the loose seal on the hose in any quantity.

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I'll update once I get the new radiator in and retest the system. I'll also try to figure out a way to verify tool calibration before then.
Any recommendations?