Excessive Heat Under Hood

Hi everyone. I have really excessive heat underneath the hood my of 1970 Plymouth GTX. People tell me its too hot, that you cannot even touch the dip stick. The factory gauge says 180 degrees to a 190. Its not boiling out. Any suggestions for why this would be happening? Thanks.

Get yourself a heat gun and run it up to temp, zone in on any heat areas... to see if you do indeed have an issue

Are the factory underhood seals in place? If the cowl seals are missing, the high pressure created at the base of the windshield may force less airflow under the hood. That said, if it's not overheating, i'm not sure i would chase this concern for very long.

Underhood heat and engine heat are not necessarily the same problem.

You could be running very normal 180 or 190 degree engine temp, but have high underhood temps. Different things can contribute--cowl seal, radiator support seals, do you run headers, fan shroud or no, ignition timing, etc.

Are you running stock manifolds or headers? Headers coated inside and out run a lot cooler on my stuff.

As mentioned, check your under hood seals AND let us know what your timing is at both initial and total. Also, curious what is your A/F readings at idle and cruise?

Reasonably priced laser temperature guns are readily available on-line.

My 440s always seemed to generate more underhood heat than my 383s; tighter fit and larger lump means a better stove, I figure.
None of 'em generated as much radiant heat as the 454 in my GMC Dually does, though.
Never had one with a dipstick too hot to touch, is that your observation or someone else's? same with "excessive"...

Although it might sound "weird" it seems if it's fresh restoration, we have a tendency to overdo it in the paint and coatings dept underhood and on the engine and related components, so it seems in some cases it "feels" like it's running "excessively hot", even though a temp gauge/heat gun say otherwise, so some additional heat may be trapped underhood, or more components are generating/radiating, or absorbing heat than they normally would if they were in their raw/natural or flimsy factory finish, I've had customers of restored cars swear it's "superheating" to on the verge of "meltdown", yet a hand held heat gun says otherwise, I've even installed thermal-couples in radiators/water pumps/blocks on running engines to prove that water temps where "normal", along with probing with a heat gun all the underhood components...so if the OP has a freshly painted engine/engine compartment, and no actual sources of high temp can be found other than the "human feel" of excessive heat, give the freshly painted components some time to age... if this is the cause?, just something to take into consideration

Every big block mopar I've owned had fairly hot under hood temps. Not necessarily coolant temps, but air temps. Also have seen no difference between manifolds and headers, although header equiped cars tend to cool off faster after they are shut down.

Never stuck a thermometer in there to check it, but its easily 200* to feel it by hand. That is smoking hot to the touch since our body temp is only 98*

My heat gun will show temps a little above 200* in various areas of the engine even with the 180* tstat, parts get hot.

You should try commuting with twin turbos, I can feel the heat rolling out from under the car at a stop with my arm out the window!

if it try to open the hood on my car after a drive, i have to wear a glove, or i'll just about leave skin on the hood latch.

I really like the heat gun idea. Wrapping headers (if not coated) helps a lot. As jbc426 mentioned, you can get excessive underhood heat if the engine is running to rich (fuel burning in exhaust) or if too lean (lean = hot)...... I think that part is right anyway.

I run a modified BB. If I open the hood, things are hot. I use a rag to pull the metal handle of the dipstick for example... too hot otherwise.

My coolant temps are fine and the car has performed well on long X country trips including the crossing Arizona desert in late summer.

I do run ceramic coated headers and I think that really helps keep temps manageable so nothing important cooks.

Install an analog temp gage near the carb. This is on a 440 - Barbecue temp gage from the home store - mounted it in the middle of the intake next to the coil. The problem being described is not normal. Tune up required. 60% distilled water 40% antifreeze and a bottle of coolant enhancer. Mopar thermostatic fan package

My steering wheel is to hot to touch this time of the year LOL. Lack of timing will heat the exhaust system up also.

The thermostat only sets the minimum operating temperature of the cooling system, the capacity of the radiator and the operation of cooling fans determines the maximum operating temperature.

Yes, I should have made it clearer that my post meant that underhood temps won't equal the tstat trigger point.

Per the original poster, this is not a coolant overtemp problem. It is the underhood air temp that is high.

IMO, that is pretty normal. You can have great coolant temps and still have extremely hot ambient air. Every big block I've had, has this condition while running spot on with the coolant temp.

Try being just a bit analytical here...do you want to fix this or not? I am a retired technical support engineer for extremely complicated technology so troubleshooting old cooling system should not be difficult.

There is an excessive heat issue here. Put the mud away that you all throw at the wall. Do you want to fix this or wallow in mudslinging? I really think you all like slinging mud. Utilizing a the process of elimination we can resolve this issue. I have dealt with this heat issue myself very successfully i might add...on more than several cars.

Put an analog temp gage under the hood like in the picture.
The cooling system and tune up must be at a fundamental basic starting point! 60% water/40% antifreeze/bottle of wetting agent. Timing and fuel mixture set properly. Min 15 degree btdc on the timing.

We have no clue as to what water pump is on here or does this engine have a Chinese alum water pump housing restricting flow.

We really don't know a whole lot do we?

Is the lower hose collapsing under load?

Manifold heat control valve not opening?

Check the temp across the radiator core while running at temp.
Make a chart of the temps - this could be a plugged core issue.

What radiator cap? How old?
Rad core - last time it was re-cored?
Rad shroud?
Fan type?
Viscous fan package?

What are the temps after a heat soak?

Does the car start by itself after heat soak [just turn the key]

After fixing the tune up, correcting the coolant package do you still have an issue?

Disconnect the transmission lines from the radiator and connect them together. No the trans will not blow up - we need to eliminate the trans as a contributing factor. 195 degrees thermostat is required btw.

There may be a significant change here then again maybe not
If the car has power steering it is very possible the pump is adding a ton of heat.

His COOLANT temperature is fine. UNDERHOOD temperature is what he’s asking about.

Pretty much everything deteriorates faster with higher temps; wiring, hoses, electronics.

Show some pictures of the engine bay.

As mentioned, makes sure all the stock engine bay seals are in place.

The radiator's efficiency is also less when it can't get rid of hot air quickly enough.

This is why front air dams are used in newer cars and also work in older cars. Especially with crowded engine bays.
An air dam creates a lower pressure area behind it and thereby helps hot engine bay air being vented away under the car easier.

Lower engine bay temps also 'produce' a bit more horsepower as the incoming aircharge stays cooler.
A cold air intake provide more power. Again, this is also what newer cars use, and also works wonders for older cars.

Make some basic sheet metal heat shields for your manifolds/headers.

Every single car and truck you could buy started running stamped sheetmetal heat shields several decades ago. They reflect radiant heat coming off the exhaust away from the rest of the compartment & down toward where air is flowing off the K frame and towards the floors. They work.

Before I made & installed mine, I couldn't even touch the underside of my air cleaner after driving the car. I just reuse the bottom left/right corner valve cover bolts to mount mine.

Who knew??? I didn't!

Sounds like a good idea. Have any pics you could share? Are these shields just flat plates that go over the headers or do they enclose the header tubes?

It was mentioned, I believe, but if you are running your timing at 32-34 this can cause the exhaust to get very hot.