Cardboard over radiator in winter.............

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I would say it is safe at 50F (+10C) or below. It should be okay to idle - I wouldn't seal the whole thing off or anything, just cover a good majority of it.
 
Depends how adventurous (and attentive) that you want to be.

I had one of these
UC5.jpg


with a 1.9 litre 4 cyl pushrod (classic Holden 6 cut down to 4).

I put the thermostat in the lower radiator hose to get the heating/cooling happening the way that I wanted it. The Varajet was leaned off badly, with EGR at idle, and full vacuum advance at idle.

The front grill part was covered (in duct tape to start with, air con tape for second effort...looks like chrome from a distance).

I left the area beneath the bumper free to access air to the radiator, from as low as possible. Removed the cooling fan, and lifted the trailing edge of the bonnet to increase the thermosyphon (of the air system).

The car could be idled for 8-10 minutes in 25-30 degree (C) conditions without getting outrageous. A slow walking pace was enough to get it back under control if the prevailing breeze upset the syphon.

Soo....after long winded post.

I resticted the cooling system while keeping the total cooling system.

Blocking off the radiator in part restricts the total capacity, and should only be used in poor ambient temps.
 
I have never understood why the thermostat does not negate the need for cardboard over radiator in the winter. If its super cold out, then just a tiny bit flows through the radiator, if its hot, then a lot flows.
 
One cold January day in Wyoming, I think the ambient temp was hovering around -30 and the wind was howling. I parked my 86 Civic Si facing into the wind and left it running while I ran into a grocery store. The car had fully warmed up on the trip to the store, but when I got back in the car to leave, the temp needle was back down to "C" even though the car was running, and the vents were blowing cool air. A few blocks away, the needle returned to normal and the vents resumed blowing warm air.
I don't think the thermostat is always effective in certain situations where the engine isn't producing enough heat to overcome the outside cold.

To prevent this from happening again, I installed the bra and slid some cardboard behind the grille screens, effectively blocking airflow into the radiator. It helped a lot. You just have to be careful to remember to remove it when temperatures warm. I've seen more than one car come into my shop overheating because the customer forgot about the cardboard. It's an 'out of sight, out or mind' situation.
 
If the thermostat is working properly, there should be no need to block off part of the radiator. If the engine isn't pumping heat, the thermostat closes down and the only circulation is through the heater core.

That said; since many cars have cross flow radiators, blocking off one side would be more technically correct,would it not?
My 2¢
 
I used to use 85- 86 Ford vans with 300" sixes with carbs as feild service vehicles. Those required cardboard to have ANY heat in the winter. Later on, I got a 94 with the injected I6. It had HOT heat in the winter without any cardboard. I never figured out why.
 
Originally Posted By: Donald
I have never understood why the thermostat does not negate the need for cardboard over radiator in the winter. If its super cold out, then just a tiny bit flows through the radiator, if its hot, then a lot flows.


Donald, a guy down here (who I bought the lower hose thermostat kit from) made a statement that the thermostat on the outlet of the engine was a great device for providing constant temperature water to the radiator.

Radiator provides near freezing water to the engine, overcooling the front cylinders (where Oz 6s and V-8s typically develop their biggest ridge).

With the lower hose thermostat, driving at zero degrees C there was no warmth whatsoever in the top tank. The block could dissipate all the heat required. Replacing the normal thermostat, the top tank would be way too hot to touch.

Many (most?) cars now control both inlet and outlet temperature.
My 1987 J-Car did, 1983 BMW does, 1990 4Runner did, and 2003 Navara does.
 
Originally Posted By: Shannow
the thermostat on the outlet of the engine was a great device for providing constant temperature water to the radiator.

Radiator provides near freezing water to the engine, overcooling


This explains it very well. If you watch the temperature gauge in the extreme cold, it actually drops when the thermostat opens. Cardboard helps with this problem a lot.
 
Originally Posted By: Donald
I have never understood why the thermostat does not negate the need for cardboard over radiator in the winter. If its super cold out, then just a tiny bit flows through the radiator, if its hot, then a lot flows.


Sounds like you've never experienced -40F! Sheltering the engine bay allows the engine to warm up much quicker and keep the coolant warmer (so more heat from the heater). The block will be warmer when you start it up after plugging in, and will retain heat longer when parked. Some vehicles (Dodge Cummins diesels, for example) will never even reach anywhere near operating temperature driving around the city without a winter front. My Mazda's transmission doesn't warm up without a winterfront, leaving the shifter and clutch very stiff.
 
Old Volvos had a crank in the interior of the car under the dash that would raise and lower a radiator screen. Many trucks mount covers/shields in front of the radiator for cold weather operation.
In really cold temps it is better all around to keep that radiator from overcooling.
 
Interesting note concerning the lower hose thermostat. Yes my temp needle increasingly fluctuates for the first few thermostat cycles as ambient start-up temps drop. There's also tanny cooler's as hinted, mine which is through the engine coolant radiator as well as through an add-on tube-fin unit, which I cover when the cold hits.

Blocking air flow through the engine compartment makes sense, and as I recall with my sister's toyota tercel on a -20's day, running the cabin heater was enough to drop coolant temperatures below normal (thermostat ok). I'm get'n chills!

Take care.
 
Originally Posted By: Donald
I have never understood why the thermostat does not negate the need for cardboard over radiator in the winter. If its super cold out, then just a tiny bit flows through the radiator, if its hot, then a lot flows.



A typical automotive thermostat (wax pellet type) doesn't regulate flow, it's only either open or closed. for example a 190*F rated thermostat is fully closed at 189* and fully open at 190*.
 
tom slick,
that was another point from the guy with the thermostat kits.

The thermostat doesn't know that there's cold water approaching unitil it gets there, which is typically a full engine volume's worth.

Closes, recirculates untilall back up to opening point and repeat.
 
Originally Posted By: tom slick
Originally Posted By: Donald
I have never understood why the thermostat does not negate the need for cardboard over radiator in the winter. If its super cold out, then just a tiny bit flows through the radiator, if its hot, then a lot flows.



A typical automotive thermostat (wax pellet type) doesn't regulate flow, it's only either open or closed. for example a 190*F rated thermostat is fully closed at 189* and fully open at 190*.


That isn't what I have observed when I have heated them in a pan of water on the stove. Not by a long shot.
 
Originally Posted By: XS650
Originally Posted By: tom slick
Originally Posted By: Donald
I have never understood why the thermostat does not negate the need for cardboard over radiator in the winter. If its super cold out, then just a tiny bit flows through the radiator, if its hot, then a lot flows.



A typical automotive thermostat (wax pellet type) doesn't regulate flow, it's only either open or closed. for example a 190*F rated thermostat is fully closed at 189* and fully open at 190*.


That isn't what I have observed when I have heated them in a pan of water on the stove. Not by a long shot.


you're right, they do operate in a narrow band, not as narrow as I illustrated but start to open at 190-195 and full open by 200-205. my point was that they don't have much regulation range i.e. allow a little water through at 150 and full open at 230.
 
Have this issue too, with our '01 Dodge diesel cummins, even in Colorado on very cold mornings....truck does NOT produce any kind of heat at city driving speeds. Takes a while on the highway too.
 
We finally got something resembling winter down here in The Swamp -- the lying dash robot read 28 F. this morning as I headed to work. Though I got heat into the cabin quickly, I noticed that the engine temp reading on the the info center reached a max of 178 F. I've seen the temp stabilize at 195 during the summer (and the fall, and the start of what's SUPPOSED to be winter. . . .), so we're talking about 20 degrees here.

Should I block off part of my radiator, then, until it warms up -- probably this weekend; bah! -- to increase efficiency and gas mileage?
 
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