Jason Hunt

OK....here's the long setup:
About a month ago I tore down my motor because I got a small pinhole in my #6 cylinder that was bleeding water into my crankcase. Sleeved the block (just #6), bought all new bearings, new moly rings, etc...put it back together.

The car was running great for a couple days, then a few days ago it started running hot. Before the tear down the car ran VERY consistently at 170 degrees, even with the fan off in town. Now when I start the car, it will warm up very quickly (about 30 seconds, which is odd) to about 170...where it likes to be. It will hang there for a while and over a period of about 20 minutes will slowly creep up to 210...then remain between 195 and 220 until I park the car, regardless of whether its idling or going down the highway. The system doesn't appear to be losing any water whatsoever, not even out of the spit tube.

The vacuum is pretty low, running at about 4 psi at idle, and getting up to a max of about 13 psi under part throttle.
I also noticed that when i break the RPM increases by about 150 rpm.
Unfortunately, I don't recall the typical vacuum capabilities of this cam, but i can tell by the brakes it is getting a lot less than before.

I've tried:
-multiple water pumps, ruling that out
-3 thermostats (and no thermostat) with no change;
-I've removed the radiator (fairly new 3-core aluminum) and done my best to ensure it's clean (flows nicely and water is clear);
-tried two temp gauges to ensure that the gauge is not at fault;
-I've used an IR temp gun to ensure the radiator temp is consistent everywhere;
-I've run straight water, water with water wetter, 50/50 coolant, doing my best to make sure there is no air trapped in the system each time i drain it.
-Running my transmission to an external cooler to ensure that the fluid was not heating up the water
-triple checked timing: 12 initial - 34 total
-Carb is not running lean as far as i can tell, plugs look perfect

My last effort was to do a compression test, thinking that I might be getting a tiny sliver of combustion gas into the water. I dont have access to a leakdown tester so this was all i had. Results:

1 - 175 2 - 160
3 - 175 4 - 175
5 - 175 6 - 155
6 - 175 8 - 150

Cylinder 6 was the one that was sleeved, do these results open up the possibility of the passenger side gasket not creating a proper seal? The car also has a very slight misfire, and I'm wondering if this could be a contributor to both

I'm running out of ideas here...help!

pancherj

Low vacuum, misfires and running hot lead me to believe timing or lean condition. Perhaps your intake is not sealing well?

Although the numbers are lower on that one bank, the difference isn't that big. On a high performance build, the numbers should be closer but yours are pretty representative of a stock type shortblock.

Get a leakdown tester and recheck. That would be at the top of my list. Also, do the starter fluid trick to look for gasket leaks on your intake manifold.

Jason Hunt

I should add that the engine is a 383, ~11:1 compression, 750 mighty demon carb, timing is curved via a programmable 6AL2 box. aluminum heads, studded with Fel-pro 1003 gaskets....that info might be relevant

I've tried several curve adjustments and have both retarded and advanced the timing....I was able to get it to run SLIGHTLY cooler (but still hot) by advancing the timing to the point where there was slight pinging at wot. I also know that the bowls are staying full and the carb is jetted/metered on the pig side. I'm assuming this would direct me more towards the possibility of a vacuum leak? I've tried the carb cleaner trick and notice a very slight drop when spraying it directly at the mating point between the heads and the intake runners, is this a common leak spot? I've never experienced a vacuum leak there before.

Jason Hunt

Typically when there is a vacuum leak...wouldnt spraying carb cleaner cause the idle to rise instead of drop? When I pull a vacuum hose and create a leak the idle goes way up, rather than the other way around as if it wants the extra air....maybe fuel making it past the venturis? Would running slightly rich cause overheating? If it is rich...it's not enough to show on the plugs.

v8sten

iTrader: (5)

modify the compression tested to hook up an air compressor, undo your rocker arms and blow air into the 2 cylinders that are low, start at cyl #6. basically doing a leak down but without the fancy gauges. and open up your radiators cap and look for bubbles, listen at the tail pipe for moving air, listen at the carb for moving air, listen in the valve covers for moving air, put your finger over cyl #8 spark plug hole and feel for moving air (I bet its the last one)

Jason Hunt

I will try this, somebody else mentioned doing this and running a hose from #8 into a cup of water to see if there are any bubbles. If the gasket has a small leak between the two cylinders, could that cause overheating? I can see it effecting my vacuum and causing the slight misfire.

jimmyblue

iTrader: (11)

There's gaskets, and there's gaskets.

My SBC400 used to give me some heat troubles. Alleged to
be a virgin with 17K miles on it, but when I finally tore into it
one side had the proper 400 gasket with the steam holes and
one was for some other SBC, without. Different colors and
everything.

Wonder if this is a possibility, sort of - maybe some kind of
crud from the recent work has found its way to some steam
hole or other restriction-point, plugging it, and is messing up
coolant flow?

Jason Hunt

redid the compression test making sure all plugs were out this time....175 all around except for #8 which was at 155

v8sten

iTrader: (5)

then that is where i would focus my attention

ZONES89RS

iTrader: (25)

I would focus my attention on an LS swap. Lol

Should have went with a new block unless numbers matching was needed.

pancherj

"I've tried the carb cleaner trick and notice a very slight drop when spraying it directly at the mating point between the heads and the intake runners, is this a common leak spot? [/QUOTE]

YES! That is a very common leakage point. IF you are noticing something there when spraying the carb cleaner, I would pop the manifold off and inspect the gasket. There are a few possibilities:

1) Bolt hole locations on the manifold are restricing the proper position of the manifold on the heads
2) Heads were flat milled or angle milled and the mating surfaces aren't parallel
3) The intake gaskets are not thick enough (you can but several different thicknesses

What I like to do is use one standard gasket (measure the thickness), bolt one side of the manifold down with that gasket and then use feeler gages to measure the gap on the opposite side.

Jason Hunt

Price was the main concern. I spent $230 for everything to sleeve the block and I would have been looking at 800+ to get another block like mine and redo all the machine work. And seeing as how I have about $4k in parts in this build, a LS really isnt cost-effective at this point...maybe a few years down the road.

Jason Hunt

UPDATE: Since my last post I've rechanged the head gasket on the questionable side, installed a brand new radiator, and put a brand new water pump on the engine....no change. I'm starting to wonder if the fact that everything is nice and tight/higher compression/etc. is having an effect on the oil temp or something

Jason Hunt

I've also ruled out vacuum leaks, No change with all vacuum components plugged, new intake and carb gaskets

v8sten

iTrader: (5)

did you do a compression test since you changed the head gasket? did you look at the sleeve when the head was off to see if it didnt drop?

Jason Hunt

Yep...good compression and the sleeve is fine, the machinist put a step on the bottom so it wouldn't drop

pancherj

Go through and check the valve lash settings just to be sure. Since you ruled out intake and cylinder head gaskets, I would start focusing on the timing. How much advance at idle and what is the vacuum reading?

I have a 750 Mighty Demon (annular booster model) on my 355. It was rich at idle and lean up top. It took some messing around with drill bits to get everything correct. It did overheat on me once when I messed with the idle air bypass and opened it too far. It leaned idle way out. Lean equals slow burn, so the mixture is burning in the exhaust port which drives a lot of heat into the cooling system.

Big Al

iTrader: (1)

First off have you determined if the engine is getting hot or the engine AND radiator is getting hot? Makes a big difference. You mentioned using a IR thermometer to check the radiator, but what did you read? You said it was all even, should get cooler as you go towards the side with the radiator cap. Unless the fans are off and it's sitting still.

Al

Jason Hunt

Rocker clearance is set at 0.015, timing is at 15 initial (idle), 34 total. Vacuum reading at only about 5 lbs, highest it will get under part throttle is about 12-15

Jason Hunt

Radiator cap is in the center, I should mention it's a center-cap, old style radiator with the tanks on top and bottom. When the gauge is reading 210+ the radiator shows around 130 degrees, the intake right at the thermostat reads about 5 degrees under the gauge