Summer grill block: how hot will you go?

[Diesel_Dave]

Originally Posted by knochenhauer

At what temperature does a typical thermostat open fully?

Each thermostat is different. Typically thermostats are specified by their crack open temp, i.e. a "190 deg stat" starts to open at 190 deg F. For most stats I've seen, full-open temp is ~20 deg F above the crack open temp.

[knochenhauer]

Originally Posted by Diesel_Dave

Each thermostat is different. Typically thermostats are specified by their crack open temp, i.e. a "190 deg stat" starts to open at 190 deg F. For most stats I've seen, full-open temp is ~20 deg F above the crack open temp.

Those numbers make sense. I removed my upper grill block yesterday to test a warm engine temperature difference from full grill block. My max operating temperature was ~20f higher than when thermostat would crack open.

Full grill block operating temp: normal range 200-214f; max 217f
Partial grill block (~70 square inch opening): normal range 172-176f; max 178f

Three important details I noticed:

1. Even with a full lower grill block my oil temperature barely approached a number that would open the thermostat.

2. The operating temperature dropped dramatically with just a minimal grill opening. It seems, for this Ford Focus at least, that a grill opening of ~20 square inches would allow sufficient cooling without operating fan.

3. For those of you running a grill block without a ScanGauge or Ultra Guage, be careful. Although the UltraGuage registered the full range of operating temperatures, my dashboard temperature gauge did not move noticeably (even while approaching 220f). Your in car temperature gauge may not tell the whole story; don't ruin your motor because of some stupid grill block.

[Diesel_Dave]

Originally Posted by knochenhauer

Full grill block operating temp: normal range 200-214f; max 217f
Partial grill block (~70 square inch opening): normal range 172-176f; max 178f

I repeat, the grille block should NOT influence the final operating temperature.

The thermostat in your engine works basically the same way as the thermostat in your house--if you insulate, open a window, etc. it'll effect the efficiency of your HVAC system, but the final temperature should end up in the same place. If your grille block is increasing the final operating temp the equivalent scenario would be like turning on your fireplace and oven in your house during the middle of summer--if your AC system isn't big enough the thermostat will keep the AC on all the time but will never be able to get the temperature down to the setpoint.

FYI, here's a plot of coolant temp vs. time for my truck:

After warm up, the temperature should stay between the 2 bands (crack open temp & full open temp). I have a 190 deg thermostat. There's a little bit of funkyness that happens the first time the thermostat opens, because the fluid has just started to flow through the radiator the first time. Shortly after that, however, the temp should stabilize between the two temps. If it still climbs and goes above the full open temp, then all the coolant is being sent to the radiator and the engine still isn't being kept cool enough--a scary situation.

Mods like grille blocks, pre-heating, etc, may affect the inital rise, but should not affect the final operating temp. The only exception I can think of is in really cold environments with very light loading, the engine may not be able to get up to the crack open temp at all without a grille block.

[Diesel_Dave]

Here's a plot comparing pre-heating vs non pre-heating.

As you can see, the preheating affects the rise to the final temp, but not the final temp.

[Miller88]

On my Focus, blocking off 2/3 of the lower grille openings LOWERS the coolant temp by a consistent 2 degrees celcius ...

[NeilBlanchard]

My thermostat opens at 184F (though after a change in the black box it may be 186F). I have never seen a temp above 204-205F; which is where the electric fan kicks on.

I have a partial grill block that only has a ~15"x4" opening in the center part of the lower grill. I also have blocked of the "escape vents" that normally allows air to bypass the radiator. All the air that comes in through the opening in the lower grill then goes through the radiator.

[knochenhauer]

Originally Posted by Diesel_Dave

I repeat, the grille block should NOT influence the final operating temperature.

You are right. Based on your temperature vs time graphs, it seems I may not have run the engine long enough. Each of my test trips were 38 minutes with an operating temp difference of 25f. I didn't realize that it could take that long to warm the engine up. Sorry about the misinformation!

Your figure were very helpful.

Just for my clarification: For the safest engine operation, temperature should not exceed the temperature when thermostat is fully open, ~20f>thermostat initial crack.

[Diesel_Dave]

Originally Posted by knochenhauer

I didn't realize that it could take that long to warm the engine up.

It typically doesn't but that's what happens when you get 50+ mpg with a 6.7L that's basically 1,100 pounds of cast iron plus 13 gallons of coolant.

[RedDevil]

I find the grill block starts to affect FE negatively long before the fans kick in.
The reason is air intake temp.
The Insight has its air intake behind the rads, but it takes in fresh air from a snorkel above the rad.
The grill block means very little air flows to the rad, so when it gets hot the heated air rises up to the snorkel rather than flow through. While a hot air intake can give good benefits, it does not work fine combined with an EGR as the recycled exhaust gas obviously is also quite hot.

On cars that do not have an EGR and work well with a hot air intake, it may well be so that the benefit of a grill block has more to do with raising the intake air temp than with actual lower air resistance...

[slowmover]

Wow, D_D, I knew that pre-heating was a help -- and that my times s. distance would be different -- but that is one impressive graph commentary on the way you drive!!

That graph would be my like leaving home and essentially coasting downhill for 25-miles.

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