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under bonnet temperatures

5125 Views 83 Replies 19 Participants Last post by  Si
since having fitted my 3" stainless steel exhaust I have noticed how HOT things get..:eek: :eek:

so I borrowed a Professional digital laser temperature gauge from work to use, its a point & pull affair all automatic..
I'll post temperatures in both Celsius & Fahrenheit

as a key I measured the car on Friday afternoon while it was cold, it had not been drive for 6 hours & the outside temp was 32/89.6

I only measured the "HOT" items ie turbo, exhaust,manifold,camcover,innerwing,rad,I/C,hot spot on bonnet over turbo..

so Fridays figures were

Turbo 33/91.4
Exhaust 34/93.2
Manifold 33/91.4
Cancover 24/75.2
Innerwing 34/93.2

now on the drive home this is 6 miles all under the speed limit so 30mph or less

Turbo 264/507.2
Exhaust 1. near the turbo flange 176/348.8
Exhaust 2. 8" away from turbo 90/194
Manifold 275/527
Innerwing 74/165.2

Rad 70/158
I/C 30/86
bonnet over turbo hot spot 51/123.8

so you can see even by gentle driving things get hot :cheesy:

TEST 1. outside temp today 25/77

now today some more testing with BOOST on a 28 mile drive using "A" Roads & "B" roads with speeds under 100mph, the last 2 miles driven sub 40mph temps taken while car was idling..

Turbo 390/734
Exhaust 1. 256/492.8
Exhaust 2. 117/242.6
Manifold 365/689
Camcover 48/118.4
Innerwing 95/203


on the drive home 5 miles on "A" roads then the longer way home on "B" roads though twisties 30 miles with speeds up to 50mph & plenty of BOOST

then the same the last 2 miles driven at 30mph or less then the temps measured with the car idling

Turbo 430/806
Exhaust 1. 270/518
Exhaust 2. 130/266
Manifold 405/761
Camcover 43/109.4
Innerwing 96/204.8

Rad 80/176
I/C 28/82.4
bonnet over turbo hot spot 37/98.6

I took the temps of the wheels & brake's too

front Inca's 44/111.2
rear Inca's 32/89.6

front brake disc's 51/123.8
rear brake disc's 35/95

God know what the temps get up to at WOT :eek: :eek: the main reason for all this testing was to see if I needed to wrap the stainless steel exhaust........


Full Throttle until you see God, then Brake...
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intercooler temp

Looks like the intercoolers doing it's job then as your getting reletively constant temps from it, would be interesting to do the same test with the standard Saab intercooler and see what happens to that (I dowt you'd be too keen on swapping back to test though!:cheesy: )

Have you found a suplier of the wrap? I've got a link saved on my work PC, they do the wrap/clips and spray paint that you coat it with to stop moisture getting in, let me know if you want me to PM/post the link.

I've just let mine idle for about 20 mins, pipework to and from intercooler was nearly too hot to touch but the intercooler(2 saab intercoolers welded in line) was only slightly warm so even sitting it seemed to be doing it's job OK, have'nt tested it on the road yet as I'm still short of a few bits to make the car road legal(front indicators mainly).

I'll be ordering some 3" piping and wrap later in the week, 3" downpipe is def the next thing to be added.
Pretty interesting. I'm guessing that you didn't do much braking, because my brakes get VERY warm in LA traffic!

Comparisons with jet-hot coating could start a nice little debate. I've read that jet-hot on the exhaust manifold doesn't hold up too well, and now I know why.
Try to make s'mores off that :cheesy:
S'mores lol, that stuff is way too sickly sweet for me!

Underbonnet temps are a concern for me, especially having no intercooler. I'm planning an intake manifold temp sensor soon - and I bet the results scare me :D
under bonnet temps

Nutcase, are you afer an inercooler & piping? I've got a spare all aluminium one from a T16s if your after one for a few pence????
Si, re:Richard (Nutcase) he can't fit a C900 intercooler as space under the bonnet of his 99T is very tight..

& please PM me the link about the wrap ;)


Sleeper Baby, No Show & all Go
Would like that link aswell Si!
me too Si - link please

exhaust wrap - links

Here's the link to the products i've found


1" Wrap:

2" Wrap:

Spray coat:

I'm gonna be getting 3" steel/wrap later in the week so if anyone does it before i do....pic's please!
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Hey when my rad fans kick in when it's 110F outside, I've put my hand in the airflow and it felt like putting my hand into a 500F oven. Driving my saab here in phoenix during the summer is putting 1980s saab engineering to the limits. I don't really like driving my saab in these conditions, but my summer car is down for now.

Oh and water injection kinda helps, especially since it's a dry heat over here, but not adequate cooling (knock knock at 12psi).
Anyone bought the wrap yet?

Did anyone/everyone find the links usefull, has anyone ordered anything yet?

PayDay for me today so i'll prob put an order in over the next few days.:cheesy:
I've have my downpipe wrapped with glassfiber webbing for over a year - not sure it reduces underbonnet temps much but it helps spoolup and low boost performance by keeping the exhaust gasses hot - esp when you have removed the CAT.
Si said:
Did anyone/everyone find the links usefull, has anyone ordered anything yet?

PayDay for me today so i'll prob put an order in over the next few days.:cheesy:

Yep, think some wrap will be on the cards for my car once I've got the other bits sorted.
and now y'all know why it is so damn important to have fresh cooling liquid and a healty thermostat and thermoswitch... :)
I though Turbos work best when there piping hot at 500 to 650 C?

I tend to agree that slow driving will not allow cold or cooler air into the engine bay, i added a by pass switch for my rad fan so when i see the temperature gauge get up to 80 c i hit the button if am in traffic or a hilly place.

what gauge of steel is used the 3 inch pipe? i suppose you could wrap it in that mummy tape stuff? does that even work?
the 3" wall thickness is about 1.5mm :confused:

HTH Paul

Sleeper baby, no show & all GO.......................
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Oh my thats a beautiful pipe!

Thats a good grade of pipe, what grade is the stainless?

I think Stainless can hold more heat than aluminium pipes, i wouldnt worry about the heat, it was probably hot under there even when you didnt have the 3 inch pipe?

You can add a ground affect scoop if you really want some cool air to scramble around the engine bay,its only affective am told if you have a hood vent, only problem is dust and water will get in there as well.

I just though of a good thread.
its 304 stainless steel only the best :cheesy: :cheesy:


Sleeper baby, no show & all GO..........................
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