overheating

[skysoldier173rd]

Just changed the heads on the engine in my 60. It's a late 80's 350. The valve guides were worn out and i got a deal on a good set of heads. Since i swaped them, i have a overheating problem. Not the timing, truck runs fine and i timed it with a light, changed nothing else but the heads. Any ideas?

[ozzyman]

Originally Posted by skysoldier173rd

Just changed the heads on the engine in my 60. It's a late 80's 350. The valve guides were worn out and i got a deal on a good set of heads. Since i swaped them, i have a overheating problem. Not the timing, truck runs fine and i timed it with a light, changed nothing else but the heads. Any ideas?

My first thoughts are: Coolant flow (possible blocked passage in the heads, gasket allignment etc...) Head gasket leak (are you losing coolant? is the coolant "boiling" indicating exhaust gasses are entering coolant) and last fuel mixture too lean (read your spark plugs to determine fuel mixture)

So I guess how and when is it overheating, rather quickly? after long drives? on the freeway? under heavy loads?

[skysoldier173rd]

it does boil, but only on longer drives. The headgaskets have pins to align them, so don't see how they could be misaligned. also, this motor runs really well. Are some heads on SBCs not compatible, but will bolt on? I ran into that once on a ford. Put thuderbird heads on, bolted on no problem, but the waterjackets did not match and i ended up with the oil pan full of water. I've never heard of such a problem though with the SBCs.

[geezer#99]

You got a coil in the bottom rad hose?
If not pump will cavitate, hose squeezes shut, no coolant flow and overheats.
Simply squeeze it to find out. If it's solid then it has a coil.

[Captainfab]

What engine were the new heads from? Do you have the casting number of them? If they happen to be off of a '93+ LT1 350, that is the problem. The LT1/4 engines are a reverse cooling designed small block.

[skysoldier173rd]

not sure, got them in a trade. I'll pull a valve cover and get the casting, but i wanted to ask about the bolt patterns of the valve covers on the heads. Thought all the old heads had the 4 bolt pattern where the top and bottom bolts were in direct allignment whereas there were some slightly offset, but still with the same 4 bolt system and then the newer generation with center of valve cover system. I thought 90s was when they went to the center bolt pattern. These have the old original 4 bolt pattern with top and bottom directly aligned if that IS a way to id them. Or does none of this really mean any particular head?

[vin63]

Originally Posted by skysoldier173rd

...Not the timing, truck runs fine and i timed it with a light, changed nothing else but the heads. Any ideas?

What do the spark plugs look like...carbon fouled, etc.? What process do you go through when checking timing? If these heads are not as efficient as the ones you replaced, you may need to add timing.

[Captainfab]

The valve cover bolt pattern covers many, many different heads. It is best to get the casting numbers. That will tell a lot more about the heads.

[skysoldier173rd]

Pulled the covers to get the numbers. 462624 on both heads. According to a internet casting number guide they are 75 to 86 76cc heads. Nothing about reverse flow. This thing is still running hot and the heads were the only thing changed here so i'm still suspicious. Is it possible the water jackets in the heads are that dirty and need to be cleaned?

[skysoldier173rd]

I found this article and wondering what anyone might think about this. Is it possible switching the intake manifold gaskets could cause my overheating. I thought both sides were the same. Also, this talks about the TBI engines. Mine has a carb.



Any chance you put the intake gaskets in backwards? They sure look the same, but if the ports for circulation are not open, that is exactly what they will do. I know how easy it is to do, because I have been there and done that. GM issued a bulletin on it years ago. Will send you a copy of part of it below. Thanks







#90-T-02: CORRECT INTAKE MANIFOLD GASKET INSTALLATION - (May 16, 1989)






MODELS: 1987-90 LIGHT DUTY TRUCKS WITH 4.3L, 5.0L, 5.7L TBI FUEL INJECTED EN- GINES (VIN CODES Z, H, AND K)







This bulletin is for informational purposes only, and should be used as a guideline if it becomes necessary to replace the intake manifold gaskets on 4.3L, 5.0L and 5.7L TBI engines. With the introduction of TBI engines, a change was made to the intake manifold gasket by adding a restrictor plate to the rear coolant passage of the gasket in order to direct coolant to flow from the front of the intake manifold, under the TBI section of the manifold (heats TBI to prevent throttle plate icing) and exit out of the heater hose pipe at the rear of the manifold (See Figure 1). Anytime it becomes necessary to replace the intake manifold gasket, it is essential that the gaskets be properly installed. If the gasket is installed backwards i.e., with the restrictor plate at the front of the engine, the engine will overheat. When diagnosing overheat conditions, the proper installation of the gasket can be checked without removing the manifold. Both the 4.3L, 5.0L, and 5.7L gaskets have metal locator tabs that can be seen sticking out from between the manifold and the cylinder head. When installed correctly, the tab on the 4.3L will be to the rear of the engine and the tab for the 5.0L and 5.7L engine will be to the front of the engine (sorry the pciture has been deleted.)

[skysoldier173rd]

The plot thickens. A picture of intake gaskets and note the blockages from the factory. I'm beginning to suspect this is my problem. The gasket set i got from Autozone was from a later model engine i found after the fact. It had the rubber valve cover gaskets w/o holes for the center bolts. There's no reason for this engine to be overheating and i'm very suspicious this may be the problem. Please tell me your thoughts Capt Fab or anyone else with experience in this area.

[glos55]

Yes I agree....

[awbrown]

Pull the thermostat and drain the engine down .. you should be able to use a light and a mirror and see if you installed them correctly... if they are istalled correctly I would suspect you installed 350 heads on a 400 shortblock without the steam holes.....

[skysoldier173rd]

I think i've got it figured out (i still could be wrong, but i'll post again after teardown and give you the results). Older sbcs take intake gaskets with open ports. Late 80s and up may take the second type pictured with some ports blocked. This has something to do with redirecting the waterflow to warm up the carb area from what i've read. Anyway if you use the ones with the blocked port, you need to put the blocked port at the rear of the engine. If you put it on the front port, the water in the head will not circulate properly and will eventually boil and overheat. I don't know what would happen on an older engine if you put the blocked port at the rear as instructed. I would not use the blocked port gaskets at all and stick to the open types. Anyway, that is my assessment of my overheating problem and i will update you after i replace the gaskets. (1st pic is the blocked type and second is the open port type) Both bolt on just fine but beware of the first one.

[ABX131]

I also have an overheating problem and have always thought it was something internal with the motor. I am convinced this is my issue. Either the PO used the wrong gaskets or they were put in backwards....I plan to pull off the intake and get a better look. Thank you for bringing this to my attention.

[skysoldier173rd]

I can't believe i have worked on engines all my life and didn't question why gaskets had blocked off ports. I guess you can't always assume everything is ok just because it comes in a fancy package or is printed somewhere or is on the internet.

[ABX131]

I wish I could show all of you the quality work the PO had done to my truck....it was a real hatchet job from every detail. The overheating issue is no suprise and I am sure it is easily fixed but it has been a major pain troubleshooting. Unless there is a mouse nest in the engine, which I have seen before, I am sure this gasket problem is the issue.

[skysoldier173rd]

it comes down to a lack of circulation caused by the restricted ports. I'm tearing mine down tommorrow. I'll post how it comes out.

[glos55]

Originally Posted by skysoldier173rd

it comes down to a lack of circulation caused by the restricted ports. I'm tearing mine down tommorrow. I'll post how it comes out.

This is really good to know! Something I could have missed too! Good luck on the tear down and reassembly and keep us updated

[skysoldier173rd]

Tore it down, replaced the intake gaskets. I used old style open port gaskets with no restrictors. My overheating problem is history. When i tore it down i noticed i had the restrictors on the old gaskets in front. If you use the restrictor gaskets, be sure and put the blocked off ports in the rear next to the firewall. Personally, i won't use them again, i'll take the old fashioned ones with the open ports. Anyway, it's a happy truck now. Thanks for everyones input.

[doobiebro]

Skysoldier its good to know you figured it out...Im a mechanic by trade and when you mentioned AutoZone I knew that was part of the problem...From my personel experience with AutoZone I always take the old parts with me because 50% of the time they sell me the wrong part...