Got a stock 5.3 with a stock temp thermostat (187 degree) and a volvo (Taurus) fan in my 67 chevelle. Dewitts aluminum 2 row w/ 1" tubes radiator, utilizing a mix of the volvo fan shroud and the chevelle fan shroud. My low speed fan turns on at 200 degrees and high speed turns on at 205. Problem is once the fans turn on, they don't turn off. Even on the freeway the car is just sitting at 208-210 degrees at 65mph. I floored it and let it downshift and after flooring it the coolant temp went to around 203 but worked its way back to 210 area. And those are speed holes in the shroud which were in there when I did the freeway testing. Let it idle in the garage after the freeway for 5 mins and it still stayed steady at 210. I have the heater hoses connected to the heater core and have the steam tubes exit into the upper radiator hose. I ran my 02 tahoe down the freeway and the coolant temp was around 193 so this is where I think I am having a problem with my swap. Tahoe still has the stock clutch fan setup in it though.

EDIT: I also have a coolant overflow bottle that is vented to atmosphere, that is connected just under the radiator cap and you can see it behind my battery in the second picture

 

shoot it with an infrared temp gun to verify coolant temp sensor.
Seems like it should cool down if you have sufficient air flow through the radiator.

What is the history on the thermostat? How about coolant? What are the ambient temps?

 

I have a infrared temp gun coming in the mail tomorrow so I will do that this weekend! And yes that's what I was thinking to, I was going to try running down the freeway with the fan removed to see if its obstructing air but I feel like its got enough surface area to not obstruct that much air. The thermostat is about a year old, only has about 2k miles on it. Coolant is about 3 old. Ambient temps were in the 70's during testing

 

Another way to remove heat is to blast the radiator front with a hose. You should extract enough heat to make certain the thermostat closes. And then your gauge should reflect that temperature. If you don't get it down to the thermostat closing temp, then I'd bet on an issue with the gauge / sender.

Doug

 

You mention fan "on" temps, but not what temps the fans are set to turn "off". With a 187F t'stat (mine too) - I see operating temps on the driver's side head temp sensor in the 195-197F range. Your "fan off" temp should be at least 5-7F HIGHER than that operating temp number.

You're not overheating - 210F isn't bad at all. A lot of the OEM LS applications have fan on-off temps that allow the motors to see 230F without a problem. I think you need to fine tune your fan operating system/programming.

 

Normal operating temperature for a majority of most vehicles is 210*F. With racing if I see temps climb to 230-240 I tend to get worried.

 

I'm not sure what temp they are set to turn off at, I am assuming their turn off temp is the same as their turn on temp, or a couple degrees lower. They are set at whatever temp lt1swap.com sets them at by default. I am going to try spraying cold water on the radiator like DW said to see if I can get the temp down below 200 and see if they turn off. I am also going to rotate the coupler I have for the upper radiator hose 90 degrees so the steam line comes in from one of the sides. I looked at it today when I got home and right now where the steam line plumbs into the upper radiator hose, its just above the radiator cap, so I want to eliminate any chance of an air pocket right there. May also disconnect the steam line and see if steady stream of coolant comes out. The 210 isn't worrying me to much, but I think I should be closer to the thermostat temp on the freeway right? And not at 210ish at 65mph


I will try this tomorrow! My infrared gun came in so i can compare the temp gun to the sensor and see if maybe my sensor is reading higher than it should. Its the same sensor that came on the engine so I have no idea how many miles are on it. I have a new electric water temp gauge thats plumbed into the pass side head and that gauge consistently reads 5-8 degrees colder than the driver side sensor. Not sure if this is normal since its comparing temps from the front of the block and back of the block though

Kind of like i replied above, on the freeway I should be seeing temps closer to the thermostat right? Like my tahoe which sits in the mid 190's on the freeway? Of course I never paid attention to the temps when I had the truck wp and fan cluctch on my car to see if this is normal temps for my swap

 

The t’stat is on the INLET not the outlet like older vehicles. So 187F inlet translates to an operating temp of 195F-197F as I mentioned before. That’s the temp I’d expect to see cruising down the interstate. Usually fan temps are set with a 5-15F temp diff between on and off. You see the problem - if op temps are 197F and you have fans that are programmed to turn on at 200-205F - and turn off 10F lower - then they’re gonna keep running once they come on.

I’ve got a stock 187F t’stat on the inlet with plenty of radiator and fan (SPAL) to keep temps stable. Under cruise, when the t’stat is controlling temps and my fans are off - it sits right at 195-197F. At lower speeds the fans control - variable speed controller that varies fan speed to keep operating temps at 202F. And that’s where the temps stay when the fans are controlling.

All that to say - what you’re trying to achieve is reasonable and possible.

 

The holes you drilled in the shroud, I would put a flap of rubber along the back side of those to keep the fan drawing through the radiator instead of through those. Your engine bay is a little crowded, not much room for the air to get out of the back, but other than that looks like you did everything right.

If the fans aren't turning off than you are not having sensor problems. Sounds like you are really running at a higher temp.

By the way I thought the temp on a stock thermostat is more like 210 degrees? Try putting the stat in a pan of water with a kitchen thermometer and see what temp it actually opens (or weather it fully opens).

By the way, 210 is nothing to worry about. A bit disconcerting that you are hitting that in 70 degree weather, but it seems to be regulating to that point so wonder what the thermostat is doing. If it is still 210 in 98 degree weather than definitely no worries. Just drive it.

 

To PopnWood's point, look closely and you'll see how SPAL put a row of openings along the top and bottom of the shroud. While moving with fans off, air can push the rubber flaps out of the way and come through pretty much the entire radiator. When the fans come on, they create low pressure between the radiator and the shroud, which "sucks" the flaps closed. That way all air being moved by the fans has to come across the radiator.

 

What do you have your fan temps set at so I can use that as a guide? I will have to find someone local to me who can do the tuning and see what mine are currently set at. So far it seems they are just set too low for my setup.

Hard to tell in the pics but I do have some rubber flaps on the back, you can see two of the flaps through the square holes curving downward towards the fender. And I just checked and when the fan is running they are being sucked closed at idle. I tested the thermometer yesterday and it opened around 188 and opened fully so that checks out. I took it on the freeway again today and with 73 degree ambient the ect sensor was reading about 203 degrees. When I got home i disconnected the fan and let the engine warm up to about 221 degrees and then i plugged the fan back in and it brought the coolant temp down to 201 in less than 20 seconds, and then it rose up to about 206 and settled around there. The Taurus fan is pretty deep, so I was thinking of ditching it and running dodge intrepid/contour fans or the dual 11" spals, that should grant me some more fan surface area and increase the flow in the engine compartment since the dual fans can exit more so around the block instead of the single fan exiting in front of the water pump. The pre 68 A bodies are pretty tight in there, I have the engine set in sbc location and corvette accessory drive so there's not a whole lot i can do to gain more clearance in the front unfortunately. I have a 1" or so gap between the core support and the top front of the radiator so I was also thinking of sealing that so more air is forced through the radiator. I probably have to weld a piece of sheetmetal there to bridge the gap so that'll wait till the next time I take the radiator out.

So based on everyone's input so far, I think I just need to have my fan temps retuned and maybe have low speed come on around 210 or so, and high at 215 ish? My thermostat has the plunger thingy and when i refilled the coolant i made sure to fill it through the upper rad hose first and fill the rad afterwards. Then i let it idle for about 20 mins while it burped some air out and i massaged the hoses too. I took measurements on the radiator and the top of the tank by the water pump outlet was 120 degrees and the bottom of the tank near the thermostat inlet was 71 degrees so the radiator seems to be doing its job.

Thanks for the help so far everyone!

 

Step 1 -- you have to CONFIRM what your t'stat temp is. If you haven't measured it in a pot of coolant on the cooktop with a thermometer -- then you don't know for certain. I've seen them new in the box be a) broken - non-functional, and b) inaccurate - opening/closing 5-7F different than the temp they're supposed to open at.
Step 2 -- once you have your t'stat temp confirmed, then you can pick fan temps. My temp setting will do you no good at all -- I'm using a different type of controller than you are. Mine is pulse-width modulated -- it varies the fan speed to keep the engine at a certain temp (202F is my set point). You're using, via the ecu I presume, different temperature settings and relays to turn the fans on full speed for a while and then all the way off when the 'off temp' that's programmed is reached.

IF (big if) you actually have a 187F t'stat - then your head temps should be in the 194-196F range when the t'stat is controlling temps. Your fan OFF temp needs to be 5-7F HIGHER than that operating range temp. If you want to control the two fans separately, then I'd have one come on at 212F and off at 202F. And the second one come on at, say 217F and off at 207F. Remember -- all that's based on a 187F t'stat on the inlet that results in op head temps of 194-196F. It also assumes your ecu is reading the head temp (location of temp sensor for computer) is in the front of the driver's side head. If any of those assumptions is different -- we start over again with the data and the math.