Sticky Clam issue.

[SquareRoot]

Talking about my thermostat here. My truck is faaaar from stock so set your OEM thinking caps aside.

When outside conditions are just right, like this morning, my primary electric fan will kick on when it's 73 degrees outside.

I have a verified 20+ degree temp difference in the cooling system between the sending unit in the head and the sending unit in the front of the manifold (see photo for location).

I'm convinced that my cooling system is so effective that under these conditions, (75 degrees outside and vehicle MUST be moving at least 20-30 mph) it's creating a hot side/cold side on the thermostat and it won't open.

I'm running a Pro-flo 4 that uses the air gap manifold. Two row all aluminum radiator. Spal dual 11" fans . Dakota Digital fan controller.

180 degree thermostat.

Primary fan set to on at 195- off at 190.

This morning the fan came on and stayed on the entire 30 miles of freeway driving to work.

Guages read 178. Fan controller read 198-200.

However, once I slow down to stop and go driving or idle, the Clam...I mean uhhh thermostat, the coolant temp evens out to normal 185-190 on both temp senders.

Odd ehh?

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[mtnmankev]

I suspect the space aliens that usually mess with me here up north have migrated to your part of the state.

 

[shiftpro]

That's very interesting... thanks.
Just wondering, what are running for a shroud with the twin Spals (best fans out there)?

What other mods does your engine have, how's the power and fuel economy?
What are your gears, tires and transmission combo?

 

[SquareRoot]

Shiftpro-

The fans are integrated with the shroud they come in. Forget the dimensions but it covers 90% of the radiator. It also has those goofy flaps that open up that allows air thru when moving. Yes, they move a LOT of air and suck a LOT of juice. But I installed a new 150 amp Power master alternator so everybody is happy.

This was new GM crate engine that I swapped Vortec heads onto and serpentine belt drive, Vintage Air AC, Hedman headers, etc.

Milage sucks but is better than it was with the carb. Here's why: CUCV axles with 4:56 gears and a th400!

That ain't gonna change until fall when I put my NV4500 package in.

However, the truck is 99% newly rebuilt now. With the efi and everything I've done to it, it fires right up and drives like a brand new 2020 vehicle.

3000rpm at 60 mph is a little annoying.

 

[Poppy 87]

I would try to swap which sensor your fans are monitoring and check results. The "known" 20 degree split seems to indicate a faulty sensor

 

[SquareRoot]

This.

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[82sbshortbed]

Oh t stat. I was gonna say, tell her to wash it first.

Or did you mean afterwards?

 

[dvdswan]

Are your fans or one of the fans wired to the A/C system?

Why would the fan come on when its 73 outside? Assuming the engine is cold.

 

[SquareRoot]

The Dakota Digital controller has an AC input. Yes, when the AC is on, the fans are on. But that's not the issue.

The controller is turning the low or primary fan on at 195 like it's supposed to. The coolant in the engine block is indeed 195.

The temp sending unit for the efi is in the front of the manifold and that coolant temp is much cooler.

Both sending units are accurate. I also verified the surface temp with an IR gun on the head and thermostat.

It's like there is hot water on the block side and cold water on the rad side. As soon as the coolant reaches 180, the stat tries to open and the cool side tries to keep it closed.


This only happens under the conditions I mentioned. If I let the truck idle till the stat opens at 180 and then hit the road it opens normally.


I'm wondering if drilling a 1/4" hole in the stat would fix it?

 

[SquareRoot]

Are your fans or one of the fans wired to the A/C system?

Why would the fan come on when its 73 outside? Assuming the engine is cold.

To the point of your question:

The engine is not cold, it's 195. The coolant on the radiator side of the stat is cold, or 73 to be exact. Having the fan kick on only keeps the radiator side cooler even longer. See the irony here?

 

[QBuff02]

air pockets? How is your top hose off the t-stat in relation to the top of the radiator? Had a similar issue on my buddy's '29 rat rod with a built 355 in it. the neck on the thermostat was a straight up design so it made the top hose go above the radiator and back down to the top tank, it would make the temp gauge and fan relay/controller do weird things because it was creating an air pocket in the system. Changed to a 15degree neck IIRC and it put the new hose down below the top of the tank and made the coolant climb to the radiator which got rid of the air pockets and his weird 20-30 degree temp differences and swings went away. Also, Which temp sender location reads which temp? Can you adjust the on/off temps for your fans? I'd be curious to see of you were able to change the turn on temp to like 215 just to see what it would do? His we had to change the switch to a different temp one on the engine when we were working on it. No adjustable control. The only other thing i'm curious about is the bypass hose from pump to intake. Most (not all) SBC's have an internal bypass pump. Not much of a vortec guy so is it a requirement with the vortec heads and serpentine system? Big Blocks have the bypass from pump to intake. But also run hoses to the heater core and radiator. Maybe your hot spots are being born from recirculating too much coolant back to the engine? Is your t-stat one with a weep hole in it to let coolant bleed past? Just spit balling some ideas here.

 

[Bextreme04]

Having it at 195 on the engine and still not flowing coolant is a bit odd with a 180 degree thermostat. I think you might also have your fans set way too low. I'm getting ready to swap an L29 MPFI 454 into my truck and I've been working over the ECU tune in preparation of the swap. The factory ECU electric fan control has the fan low speed output kicking on at 215 deg and the fan high relay doesn't kick on until 235 deg. I'll probably lower those a bit, but having the low fan come on at 195 seems really low to me. Especially if you are reading that temp at the cylinder head. I've also got an original 4 row radiator and the Ford Windstar electric fans with a custom wiring harness that is very similar in design top the factory 2006-up electric fan setup.

 

[SquareRoot]

QBuff02,

Good info.

The sender in the block feeds the fan controller.

The sender in the intake feeds the efi/guages.

I could adjust the primary fan temp to come on later like 210 to keep the fan off but once the stat opens and everything equalizes I'd be stuck with that setting.

The infamous bypass hose: When putting Vortec heads on a non Vortec block you should add the bypass hose as I have done. That allows the coolant to circulate inside the block until the thermostat opens thus preventing hot spots and cracked heads. True Vortec blocks have a cast in internal bypass.

I "think" my stat has a small hole in it but I'm not 100%.

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[Turbo4whl]

My vote is also, air pocket. All thermostats should have a bleed hole, (my opinion) but they don't all have one. Yes, drill the hole, even a 3/16" or smaller hole is enough to let the air out from under the stat.

Thermostats have wax in a mini spring loaded piston/ cylinder. Hot air will not make the wax expand, needs hot coolant to work properly.

 

[SquareRoot]

90 degrees outside when I left work. Fired it up, idle for about a minute. Hit the freeway and drove home exactly the same as I drove in this morning. Thermostat opened at 180 (coolant temp in the head read about 8-10 degrees higher). Within about 2 minutes both temps maintained 190 all the way home. The fan never came on until I hit a red light one block from the house.

So my question is; Can an air pocket be intermittent?