Recently I have been measuring under bonnet temperatures. My car is a 1985 V12 coupe with the cruise bellows removed, good aircon which is on all the time, and with the cooling system in top condition. Additionally it has a slot in the front bumper to admit air straight into the radiator stack, with the horns also moved out of the way. I have NO foam round the radiator and a separate transmission cooler. Therefore the airflow into my engine bay is far better than standard.


I have recently purchased a digital measuring device that runs two channels to a unit in the car. One sensor is strapped to the rear of the engine just aft of the capstan, one to the front, just behind the aircon compressor, both are suspended in the air about 2 inches below the bonnet.


These are the results so far at ambient 27 degrees C, aircon on, 12 inch aftermarket electric auxiliary fan on (replacing OEM auxiliary fan). Water temps remained stable and well below 90 C at all times in these tests:

• On the move above 40 MPH the front temp is about 56 C; the rear is about 52 C
• On the move below 40 MPH front temp rises to about 60 C and rear to about 56 C
• Once stopped, engine off, bonnet closed, both temps rise to 80 to 82 C immediately. These temperatures do NOT fall significantly after ONE HOUR if the bonnet stays closed. An open bonnet immediately reduces air temps to about 50 C. Even with the bonnet left open for an hour, air temps at the sensor are still 46 C
• On the move again temperatures drop to under 60 within a mile or two. If the main electric fan is manually switched on (it does not trigger on my car until a 90 C water pump inlet temp), temperatures drop slightly faster.
• At rest, aircon on, engine on, auxiliary and main electric fan on: At rest after a run, simulating a traffic hold up, front air temp climbs very fast to 70 - 72 C. Rear 4 C lower. Water temps remain stable, possibly dropping a touch. The extra air temp I attribute to the main fan pulling large volumes of air through the rad to keep the water temps stable, and thus extracting substantially more heat from the coolant, while air is not being extracted from the engine bay as well as it is when on the move. In fact, at rest air temps climb when the main fan is activated, though water temps fall.

Conclusions:

• The front of the engine bay is normally hotter than the rear.
• The air temperatures under the bonnet on the move are, at about 60 C, not excessive. Therefore louvres are not necessary to preserve reasonable on the move under bonnet temperatures
• Cold air intakes are definitely worth it as they reduce intake temps to ambient (ie 33 C lower than under bonnet air temps).
• At rest, engine off, under bonnet temps rise very fast to a high, loom-cooking and rubber component-cooking level (80 to 83 C).
• Opening the bonnet after you stop WILL definitely substantially help preserve the wiring loom and all rubber components from heat damage.
• Louvres would greatly reduce under bonnet temps once the vehicle is stopped.

I will repeat these tests when (if) we get a day with ambient temps over 30 C.


I attached temperature strips to the oil sump, oil filter, oil cooler in, oil cooler out pipes and A bank cam cover at the front top. Oil temps showed a maximum of 85 C throughout the oil system, including the oil cooler inlet, except for the oil cooler outlet which was 77 C. My car has the bypass oil cooler system. From these temps I conclude that the bypass system does indeed cool the oil efficiently and that there is plenty of flow though it - if not the oil temps would not be the same as the sump and oil filter.
The can cover temperature maximum showed 95C. All these temperatures are well within the oil's correct working temperature range (Shell Helix 100% synthetic 5W 40).
Greg

 

Greg:


I add my thanks.


Interesting and validates my thinking and that of others far more
talented than I. Air comes in, absorbs heat. Let the hot air out!!!


Most, if not all early USA cars recognized this and provides exits in the side panels. Splash and bonnet/hood.


Some of us merely removed the hood/bonnet side panels . Partly
for air flow ands probably mostly to show off a nice engine...


Pop the hood/bonnet in extreme heat works. Done one way or another for decades.


Fortunately, in spite of 100 F + temperatures, my lump stays on the
preferred 90C. Big four row brass radiator. Twin PCM managed E fans and an electric water pump !!!


Coco snoozes in the path of cool air from the AC here in my "work
room". Smart dog!!!


Carl

 

I'm planning to replace both fans with reversible electrics. The plan is to reverse both on ingnition off and run both on a timer limited by a voltage check to prevent battery drain.

Drawing air from under the car through the engine bay and dumping it out the grille should be far more effective than trying to push hot rising air out the bottom of the car.

I've yet to source the fans, relays and timers circuit components, and I thought I'd ask here first if anyone has already implemented such a setup. I thought I was very clever with my brass door bushings for throttle bushing replacement until I saw that idea had been posted long before I got a jag.

 

IMHO it is crucial to have foam around the rad as well as the proper plate under the chin spoiler to direct air through the rad and to let air extract properly under the engine compartment. What we really need is a good wind tunnel test to "see" flow characteristics and extraction at different speed. I can tell you a quick test is I put my cover on the car and leave the grill open and tailpipes open, start the car and the cover stays flat on the hood/windshield. Remove the seal on top of the cowl under the hood, close it and restart and the cover instantly balloons up off the hood/windscreen. Needless to say my seal stays removed and I also pop my bonnet and lift it after every run and put a stand fan directed at the underhood for approx 30mins.

 

Hah!

The "experts" in the later model forums will tell you that this
is of absolutely no concern and that "modern" engines need
to run at 95C plus to prevent all kinds of imagined deficiencies.

No matter. I still run a cooler thermostat and achieve both
closed loop fueling as well as full heater output in any
weather down to -35C.

 

First thanks to Greg for illuminating information.

With regard to engine cooling thermostat I gave a lot of thought about what temperature specifications to get for my 6.0l before choosing the Jaguar recommendations for 88℃ (EBC3577).

In my research on electric cooling fans I have learned that modern fans are capable of much higher airflow capabilities (cfm) and also that the airflow varies with resistance (static pressure) and in Jaguar application where the engine cooling fan has to draw air through oil cooler and then air conditioning condenser before getting to the water radiator a fan that can maintain high airflow against high static pressure is needed.

 

That is so at rest, I have done something similar. BUT, big but, on the move it is a very different story. I put wool tufts all over the bonnet and in the gap between the closure and the scuttle, first without the seal. The wool tufts on the move are sucked BACH down into the engine bay, and the wool tufts on the last foot or so of the bonnet also show stalled air. So although at rest without the seal, fans on, air DOES exit from the gap at the cabin end of the bonnet, on the move it did not, but in fact the flow reversed. I was really surprised by the result, which was the exact opposite of what I had believed and held to be true! Just shows you must measure things. See post number 30 in this thread:
https://www.jaguarforums.com/forum/x...-160604/page2/


We are totally right about popping the bonnet at rest, I have always done so, much to the scorn of many who held it did nothing etc etc etc, and now I know it really is effective.
Greg

 

Well done Greg.

The rear engine bay temps were a surprise of sorts, but fact is fact.

The heat rise at stopped is no surprise. I removed that safety hook, coz it was waaaaay toooo hot to push to open the bonnet at times. So now the bonnet simply "pops" up on the catches and a quick lift of the hand opens it, and the HEAT rises.

As you know, I run the Ford E fans, and NO foam at the radiator. Also I have replaced that thick trans foam with "modern" thin stuff, AND I know that engine bay exit air is sooooo important.

That chin spoiler is mandatory, to assist create a negative zone under the car, whilst in motion, to assist in the "drawing" of engine bay air out the underside.

When I rewired mine, i wrapped all the loom I could with "header wrap" to help protect from that heat.

The last summer here was hovering around 45c, so under that bonnet was a tad warmer than most, and NO issues at all, even with the fuel rail, that many claim all sorts of evil.

WELL DONE AGAIN GREG.

 

Very good information.

Here's what I did for my 720hp supercharged Camaro. These particular vents even have a splash tray underneath in case you get caught in rain. They worked brilliantly with some fan controls. I was able to hot lap at the drag strip and get the engine (including coolant temp) down to normal operating temps in the space of a song.



I may be doing something similar on my upcoming LS swap.

Padre

 

Padre:


Those louvres are really nice. I think Alyn welded in something similar on his lumped S3.


I've popped the bonnet on my XJ wuzza six lump after a run on a hot
day on more than one occasion. No after run fan fitted. I have one.
But, decided it's obstruction of incoming air more detrimental than beneficial. My opinion, anyway, right or wrong. Probably a bit of each. And, when I shut it down, the thought of walking away with something electric running bothers me. Complete electrical shut down would be best. However, there are memory circuits that need to
run.


Historical anecdote: My school chum's parents had a pristine 39 Ford
Standard four door that saw them through the WWII years. But, it's 221 CI V8 got very tired. His Pop's friend was connected with the local Mercury dealer. Solution, a brand new 59A 239 CI engine. A bolt in replacement. Ran very nicely, but suffered an over heat issue. Odd, as many other old Fords did well on that replacement.


After much messing with, a bodge worked. Sorta. The fourth ring, an oil control function removed. friction reduced, engine ran well and cool. But, with a huge thirst for oil. Roy's pop decided "enough is enough". Bought a nice white 49 Ford tudor. Not a Mercury? A lost friend?


The 39 got passed down to his son, Roy.


Just not enough radiator and air flow for more BTU's!!!


Fun with the car another tale.


Carl

 

This is somewhat correct. Later model cars run much tighter tolerances and as such need the additional heat to expand components to operating temperature tolerances. An extreme example is an F1 (or even the Ossie V8 Supercar) engine which is so tightly toleranced it must be pre-heated prior to starting.

Remember most of the wear in an engine occurs on warm up. And running too cold a thermostat can cause a few issues.
- Engine does not reach operating temperature as set in the ECU, so engine is always running in cold enrich.
- Oil does not reach operating temperature, needed to burn off contaminants, such as water etc
- Excessive engine wear if components are not at manufacturers operating envelope.

Hotrodders have been running SBC'c cooler to prevent detonation enabling more advance, but I saw the results of some NASCAR dyno testing on a stock SBC and max power occurred at 205-215°F. Having good quench and squish would probably accomplish the same thing.

BTW NASCAR teams run 160°C (240°F) engine temperatures.

Greg's post was more about engine bay and after shut down temperatures

 

Before the above is accepted as fact- is it possible to move one of the two probes so that it is measuring the temp of the air actually entering the engine?

You might be surprised by the outcome.

I own an older Corvette that came from the factory with a ram air inlet system to supposedly take advantage of not only cooler, but higher pressure air at the bottom of the windshield area while at speed.

Contrary to GM's marketing claims, witht he car at legal highway speeds, the difference in temps with the system in full operation vs. blocked off were only 1 or 2 degrees and those temps were within a few degrees of ambient anyway.

Quick calculations indicated that the car had gained less than 2HP from the cooler air.

 

Great testing/research.

What I think would be interesting now would be to measure the engine bay temps of a variety of cars for comparison.

Cheers
DD

 

Here is an extract from Allan Scotts book, these are dyno runs on a Jaguar V12 he did when they were doing the R&D for 6.0L TWR engine.

The pertinent ones are Tests 1, 2 and 3.

Test 1 is a base line on the stock 5.3L V12 with exhaust.

Test 2 is with only the Group A exhaust manifolds and open exhaust.

Test 3 is as Test 2 but with TWR cold air intake larger air inlets and K&N filter, there is nearly 20hp difference but what is more interesting is the power is above Test 2 in the whole test band.

 

A car sitting on a dyno has little to do with real world on the road.

 

We are promised a hot day today Mikey, so I want to do a higher ambient test to see what the air temps under the bonnet change to, if at all.
Once that is done for the next run I will move the probes to:

1. The OEM inlet trumpet, and
2. The AJ6 engineering extra cold air inlet I have that takes air from under the bottom of the rad stack.

So that way we should get a valid identical-conditions comparison. The AJ6 Plus Torque stuff has a second inlet to the air box underneath the box, and a tube to a second trumpet. Thanks for the suggestion.
Greg

 

Warrjon
Indeed it was, as I am not at all concerned by coolant temp problems on my car. What does concern me is the degradation of the loom and rubber components and that is why, as you say, I am measuring air temps above the V, both on the run and at rest. In my opinion it is these items that are the biggest reliability-affecting things on the V12, given poor or irregular maintenance.


I also wanted to actually know what oil temperatures were doing, as there has been lots written about the efficacy or otherwise of the bypass system. I was pleased and relieved to find out that oil temps are fine and that the bypass oil cooler system works well. later in August I am planning a longer all-day trip with lots of stops and starts and fast parts, so that will give me more data on max oil temps. But for now, I am pretty sure all will be well.
Greg

 

Intake trumpet temperature measurements:
All measurements were taken 1 inch inside the B bank intake trumpet
Ambient 29 C, car fully warmed up, aircon on, 12 inch auxiliary fan on.
At 50 KPH (30 MPH): B bank trumpet :68 to 72 C (Front of V behind compressor 68 – 70C)
At 70 KPH (50 MPH): B bank trumpet 54 C (V 64 C)
At 120 KPH (70 MPH): B bank trumpet 47 C (V 60 C)
At rest, as in traffic after a hot stop, main 17 inch electric fan on: B bank trumpet 82 to 84 C (V 78 to 80 C) . Interestingly, the intake temperature is HIGHER than the V under these conditions. I attribute this to heat coming off the exhaust and rising, which at higher speeds does not happen
As soon as the car starts off both temperatures fall very fast. Within 30 seconds at 100 KPH they have dropped to their normal values. This is a result of my extra clean air slot set into the bumper. Standard spec cars will take considerably longer to reduce under bonnet and intake temperatures.
Below 50 KPH (30 MPH) but still moving, both temperatures are in the 70 to 75 C range.
Conclusions:
Air temperature above the V is about ambient plus 35 to 42 C depending upon speed.
Air temperature at the intake trumpet is about ambient plus 25 to 32 C depending upon speed. That is, they are around 10 C LOWER than the centre V temperature, but still well above ambient.
Both intake and V air temperatures are equally hot at speeds below 50 KPH (30 MPH)
Cold air intakes are definitely worth it as with them intake air temperatures are reduced by a minimum of 25 C at ambient temps above 24 C. Remember also that my car has superior airflow through into the engine bay than OEM cars. Therefore on standard spec cars the cold air intake temperature reduction may be greater.
The electric fans control coolant temperatures very well at slow speeds or at rest, engine running, but do NOT reduce under bonnet air temperatures or intake air temperatures.
A louvred bonnet would probably benefit air temps at speeds below 70 KPH (50 MPH), and also in stationary traffic and post switch off. I intend to butcher an old bonnet I have and find out!
So Mikey, you were more correct than I had thought, intake temps are lower than V temps, but still quite a bit higher than ambient.
Greg

 

Thanks very much, that's great data!

 

Thanks Greg,

Always enjoy reading your test and this one was very interesting and informatative. Thats why I respect your know;edge and input on things