: 1968 472 motor questions

07-09-11, 02:19 AM
Ok guys newbie here. I/we, me and the wife. Have a '68 convertible with a 472. The motor is a '72 472. Seems to be running hot. Just rebuilt the motor. Motor was hot tanked, new cam bearings, new cam, it's not stock but just above stock. Comp cam. new lifters. New springs matched to cam. Stock bore and pistons. new bearings throughout. Stock rockers. new water pump. Pertronix ignition. Probably need to replace vacuum advance module, it doesn't seem to change when vacuum hose is pulled off carb to set timing. Timing is at 8 degrees. I don't remember what total advance is. Good oil pressure goes to about 45-50 when fired idles down to 35 to 30 when hot, 40 or so when driving. Stock intake and exhaust manifolds, duals to back. Running stock quad carb. Has ac pump on motor. A.I.R. ports blocked off in heads. Think thats about it. 180 thermostat. new plugs. Has about 80 miles on it now.

Ok now to problem. Exhaust ports on heads at the manifolds have turned white did it almost right away. The intake manifold at the middle right has also turned white hot now and the opposite side where the choke coil spring has gotten a little warm also. The carb has not been rebuilt, trying to get to it. Not too confident on rebuilding myself. Temp gauge stays under half way idleing, it has overheated a couple times but got it cooled down ok. I have ran a Carter carb but it's too small, only a 625. plugs look good, not white hot or looking lean, they have some fuel residue on them. I do think the carb is trash, but it ran the same with the other carb, just not enough fuel with the Carter.

I need some direction and guidence on where i'm at. I'm concerned I might burn it down by running it too lean. It seems it is lean by the heat on manifolds and heads but plugs don't read like they are lean. Any ideas??? I do have another Quad that i'm thinking of trying, probably will do it sat. I am using stock temp gauge but will install a after market temp gauge also.

Thank you. Mike

07-09-11, 07:08 AM
Iīd rather have back the original Rochester quadrajet carb than a Carter. Itīs not a carburetor designed to be fitted to this engine. I think original equipment always works best.

You say temperature is normal when idling. When has temperature gone high (high speed like 100 mph for a long time, climbing a long hill...) and which temperature marked the gauge needle?

Sometimes a richer blend improves temperature; also advancing distributor but I think you can not vary the pertronix.

Did you flush your cooling system? If you did and it still gets hot, you can also try to get a coolant with a high cooling power like the Volkswagen-Audi G12.

07-09-11, 09:47 AM
I think the aftermarket gauge is a good move to try to get a handle on this. I just put a rebuilt 400 in my Chevy convertible and it was overheating a couple times but it was just the thermostat sticking. I could watch the gauge go to 230 then all of a sudden it would open and go back to 180. It did this for 2 days and I was about to drain the coolant and change the stat but it finally started working correctly now. The gauge really helped me figure it out. Hopefully when you get a gauge on it you can watch it warm up and see the thermostat opening. We can hope it is something this simple. Timing can affect overheating so I have heard but I have never had any experience with incorrect timing causing overheating. Let us know what you find out.

07-09-11, 01:10 PM
I would flush the cooling system really well. May be some old loose crud blocking flow, and also get all the air out you can.

Marty at 500CID.com is a great source for parts, tips, etc.

It could be not one problem, but just a little of this and a little of that. Like, timing and..., adding up.

Barker Gang is good as well. I had them do my Q-jet this winter. http://quadrajetcarburetors.com/

07-09-11, 01:31 PM
I Agree with Dirtywaterdiver. In many cases overheating comes from many little problems. An example: My '73 Dodge was overheating even when engine was taken off, head done, cooling circuit deeply cleaned, water pump changed... But radiator were not in good condition so no matter how many times I flushed the circuit. I even installed an additional electric fan, got closer original fan to radiator... Finally I changed radiator panel and the thing improved a little but not enough. Then, I took head off and we realized that there were 2 holes missing in the new head gasket (As there are engines requiring additional holes and standard ones, manufacturers make only standard engine gasket so you must check if you need additional holes to be done). Got a new gasket and made the missing holes. Since that day no overheating.

07-09-11, 01:48 PM
I'm with everybody else in saying the thermastat and making sure there's no air in the system. The Olds I had ran a little hotter and burned the paint near the exhaust manifolds, it eventually bled the air out. But hot to a Caddy motor is 260. 220 is where they started adjusting timing but the temp light doesnt come on till 260.

07-09-11, 02:36 PM
Firstly, the Q-jet should probably get boxed in favor of something better. I'm not a big fan of Carter carbs. In fact, I hate them.

On to the overheating. Could be Thermostat, air locked cooling system, water pump, or as simple as a bad gauge or sending unit. The 72 motor has a slightly lower compression ratio than the 68 did so running on pump gas shouldn't be too tough on it. If the plugs aren't burned up it might be something quite simple. I'm assuming the non stock cam has been degreed in properly..

07-09-11, 03:38 PM
Also, wasn't the OEM thermostat a 195 Degree?

07-09-11, 03:55 PM
Oem stat is 180. Cam put in straight up. Quad is junk right now. When I had the Carter on it I could get it to idle good, but driving down road and highway it just wasn't big enough so it was sluggish and would hesitate. You could feel it jerking like it was starving for fuel. I got the water temp to stay around 1/4 to just under half way up. But my concern about the exhaust by-pass to intake manifold that goes up under carb kinda has me concerned. It just seems way too hot. Maybe it's me tho. This is my first caddy motor so i'm learning as I go.

I really appreciate all the replies and info so quickly. Thank you guys. Any more info is welcome. Going back out to work on it. Mike

07-10-11, 02:21 AM
There is a valve, at the end of one of the exhaust manifolds, before it connects cross over pipe (if you don't have true duels). The valve is supposed to be closed at cold start up, to block the exhaust and redirect it under the intake manifold, to warm the carburettor. As the engine warms up, the valve is supposed to open, allowing the exhaust go through the cross over pipe. If you have true duel exhaust, then it will just block the one side of the system until the engine warms up.

Either way, if the valve does not open after the engine reaches operating temperature, it can cause the intake and manifold to overheat. I've seen the top of an engine glowing cherry red because the valve was stuck (and the jagoff behind the wheel didn't smell the hoses melting), so the intake and exhaust turning white hot wouldn't be out of the question. This problem can also cause the engine to boil over.

A lean running condition would NOT cause anything to glow.

07-11-11, 12:33 AM
Valve is not there.

Ok been playing with the car today but it runs like crap. I figured it has a miss on cyl 1,7,2,6 on idle. It has spark, plugs are good. It seems to try and even out when its getting more throttle, but still misses. It has the carter on it right now. I know it's a crappy carb but the quadrajet runs worse. Is there a problem with the carter that it doesn't feed the cylinders properly or is that more because of the adapter that is on the manifold to adapt the Carter. I need to find a good Quad to put on it. I'm more lost than before.

07-11-11, 11:18 AM
Thatīs right. You need a reliable carb on your car and once carb negative effects are discarded, start checking elements related. You can get a remanufactured Rochester for $ 190 from www.Rockauto.com, sending your old carb, and a lot of Edelbrocks at ebay http://shop.ebay.com/i.html?_nkw=68+cadillac+carburetor&_sacat=0&_odkw=69+cadillac+carburetor&_osacat=0&_trksid=p3286.c0.m270.l1313 Donīt know how Edelbrock goes on this engine but it seems to be selling well. This is selling for $ 160+shipping: http://cgi.ebay.com/ebaymotors/Edelbrock-1400-Carburetor-NR-_W0QQcmdZViewItemQQfitsZYearQ3a1968Q7cMakeQ3aCadil lacQQhashZitem20baf784daQQitemZ140575737050QQptZMo torsQ5fCarQ5fTruckQ5fPartsQ5fAccessories