View Full Version : Aluminum Risers...How hot is too hot?

07-07-2013, 12:02 PM
Just installed a pair of new aluminum IMCO manifolds and risers on my 1990 4.3L

The manifolds are fine but the risers get really hot. Temp gun says 140 degrees at idle...couldn't get a temp reading at running speed but it felt about 200 degrees...not scalding, but still realllllly hot to the touch.

Is this normal for aluminum? How hot is too hot?

07-07-2013, 12:54 PM
I have AL manifolds & risers (GLM) on my small block. There is a slight temp differential between port & starboard due to the way the water is routed through the block and t-stat housing, at least with an Alpha. At idle they are both cool enough to touch and stay between 120 and 140 on the temp gun; this is with a 140 t-stat. After a hard run the port gets to 140-145 and I can still rest my palm on it. Stbd gets up to 160 and feels like you could fry an egg on it. Just a 15-20 deg difference but it is a pretty big contrast by touch! The temp won't drop that fast after a hard run - you've got a couple minutes to pop the hatch and check things out. Use the temp gun and shoot your whole motor at idle and when hot. Exhaust, temp senders, t-stat housing, oil filter, oil pan, intake manifold, etc. Get a good feel for what your baseline is and then you'll be able to ID an impending cooling problem before it's critical. What temp t-stat are you running and what does the gauge say? Any difference from prior to the exhaust switch?

Bottom line, unless you've got a cooling problem I doubt your risers are getting to 200. If they are you probably need to troubleshoot your cooling system because you're not far from starting to scorch your exh. hoses. The AL is a lot more effective at transferring heat than cast iron and mine have always seemed "hotter" to the touch for whatever reason. Also, make sure you re-torque everything (esp the manifold-riser joint) after a heat cycle or two.

07-07-2013, 07:44 PM
I had aluminum log manifolds and risers on my last boat. The risers were always waaayyy hotter than the manifolds. If you say they are not scalding hot...then you are fine.

07-07-2013, 10:17 PM
Duckhunter- Thanks for the recommendation. Eager to get back out there with the temp gun again and check things more thoroughly. My main concern is that it heated up so quickly- only on plane for less than 5 minutes. But I suppose aluminum will heat up much quicker than cast iron.
I'm pretty sure it's a 140 thermostat...of course the temp gauge went out on me but the gun said the block was about 140. Can't really say what the contract is to the old manifolds. Been a couple years since it last ran with them on there.

Yeller- That makes me feel a lot better. I've had enough headaches so far this season :banghead: Hopefully the temps aren't as high as I initially thought. I'm kinda paranoid now after frying a few connectors with my old manifolds.

07-08-2013, 10:40 AM
You will see higher temps at the risers than at the block, I have seen 170 with a 140 Tstat.

07-09-2013, 09:19 PM
Ok, so I took her out again tonight. Put some blank label stickers on the risers so the temp gun could get an accurate reading (didn't like the shiny polished aluminum:shades:)
Temps at idle were about 130-140 all around. Got up on plane, cruised for about 10 minutes. took temp readings intermittently. Engine and manifold temps rose to about 145. Riser temps climbed to about 200 and stayed there.
I thought this was a bit warm, but I wasn't terribly concerned since they weren't rising any higher sooooo I did a high speed run.....

Then something strange happened...

The risers actually cooled off. All the way down to about 140. AND THEY STAYED THERE! It was almost as if i blew out something that had been restricting the flow...but I have no clue what it could have been???