Underhood Temperature - Fuel Economy, Hypermiling, EcoModding News and Forum

Big Dave · 03-19-2014, 04:18 PM

Thinking grille block.

What is the acceptable limit for underhood temperature? The engine coolant doesn't worry me - I run pure glycol. The intercooler isn't that important. If the A/c quits, I'll know it. But melting stuff under the hood is bad news.

Big trucks have engine compartment vent openings on the side.

Any ideas about temperature limits?

Anybody put a gauge under the hood?

cbaber · 03-19-2014, 05:17 PM

I don't have a specific answer for your truck, but most most OBDII cars have intake air temperature sensors. I can read it on my ScanGauge. I've blocked off the outside vents to my air intake, sort of a warm air intake. I've seen temps as high as 140 degrees on the hottest days. If anything it helps my fuel economy, especially lean burn and warm up times. My advice would be to have a way to monitor the temperature. Intake air temp is one way to do it if you have a scangauge or ultragauge (although it may not be as accurate if your intake sources air from outside the engine bay). A cheap remote thermometer is another option. You could monitor the temps for a few days under a few different conditions to make sure it stays within acceptable limits. As far as those limits go, you are probably safe up to 150 degrees, maybe more. Most critical heat sensitive components are protected with insulation, and temps shouldn't effect them unless they come in direct contact with something hot.

RedDevil · 03-19-2014, 05:28 PM

Before I had my UltraGauge I had a cheap digital in/out thermometer on the dash, with the out temp feeler in the air intake. It even works when the key is off.

I could see it rise when waiting at the lights with the engine off, as the heat of the engine heats up the then stagnant air in the intake.

Cobb · 03-19-2014, 06:02 PM

Ive blocked grills of a few cars and rental cars with no problems. Now if you are talking about your truck you may want to leave some room for air if you are hauling/towing anything. If its just you and you are eco driving them Id block the whole thing off if you can watch your temps.

Its my experience truck drivers/owners are more concerned about the exhaust temp than anything else.

ksa8907 · 03-20-2014, 12:10 AM

Ive seen over 200f in the intake, part of that was egr though.

campisi · 03-20-2014, 12:37 AM

Quote:

Originally Posted by ksa8907

Ive seen over 200f in the intake, part of that was egr though.

Wow! I've got a warm-air setup kludged in my Forester and monitor the intake air temp. I've seen it go as high as about 126 to 130 deg and I start to worry at that temp. Yall think that 130 to 140 would be OK? I remove the WAI and go back to stock in the summer.

ksa8907 · 03-20-2014, 08:43 AM

My sensor is a map/iat sensor in one, so it is measuring egr as well. I have no issues with those temps except on moderate to high load. I posted in another thread about mixing e85 to offset the extra high temps.

On the subject of the OP, as long as your heatshields are in place I wouldn't be too concerned. That stuff is designed to handle heat.

gumby79 · 12-10-2017, 03:23 AM

Before I wraped my exhaust manifold and turbocharger I was mesuring component(not air) temperatures @250-300°f after 1 hr @65mph, can't tuch anything ,with an IR temp gun...
after 100-150°f at the top of a grade after pulling900°f EGT for 10min and 650-800° f for the previous 30min with a grill block on my 1st Gen Cummins during summer. Pop the hood and grab a hand full of turbo snell and hold on to it warm but not bad . More power 1/2 as much lag, doing more with less (more efficient) . (You have a waste gate to solve lag but this would help) the components under the hood are designed with the specific heat zone of its intended use. I would say 350°, plastic starts to soften. So this would be my upper limit. IAT is no good for me and you, for reading the under hood temps . Our turbocharger heats the air when it compresses it. Then cools it with the IC we blocked .

slowmover · 12-10-2017, 04:25 PM

Had a pair of Jeeps that ran extra hot. Literally couldn’t open hood without gloves. Items mounted on firewall (hard plastic) showing 250F on temp gun

I shimmed up hood hinge and modified weatherseal on the side of hood that didn’t receive airflow for HVAC. That helped. A little too efficient in winter so removed shim. W-S mid was adequate year round.

The constant heat in Texas will eventually toast all plastic under hood. Cracks off or crumbles. Be reasonable about this. It becomes a never-ending chase of hard to find parts.