1974 258 Head Gasket replacement

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I have a 1974 amc 258 that runs great.  Bought January 29, 2015. drove it a little while the day time temps were in the 50s just a little and did not notice any over heating temps hit 70 and the temp quickly jumps to 230.
Thought it was the fan shroud (had newer radiator when bought) very pourly done.  So i pulled the radiator and fixed the shroud.  Still over heats.

replaced the leaky tstat housing and new thermostat.
new water pump(old one looks pretty new)

at idle it does not overheat.  with the radiator cap off and just a little throttler lots of bubbles. 

I rented a block tester and it did not turn yellow.  So i drained the antifreeze that was 40/60 and just water bubbles like crazy.

So I have decided to pull the head.  In two weeks i will have it tested.

engine

all the plugs look clean 6 to 1

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gird123 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2015 Location: Nevada Status: Offline Points: 45	Post Options Post Reply Quote gird123 Report Post Thanks(0) Quote Reply Topic: 1974 258 Head Gasket replacement Posted: May/20/2015 at 6:46pm
	I have a 1974 amc 258 that runs great. Bought January 29, 2015. drove it a little while the day time temps were in the 50s just a little and did not notice any over heating temps hit 70 and the temp quickly jumps to 230. Thought it was the fan shroud (had newer radiator when bought) very pourly done. So i pulled the radiator and fixed the shroud. Still over heats. replaced the leaky tstat housing and new thermostat. new water pump(old one looks pretty new) at idle it does not overheat. with the radiator cap off and just a little throttler lots of bubbles. I rented a block tester and it did not turn yellow. So i drained the antifreeze that was 40/60 and just water bubbles like crazy. So I have decided to pull the head. In two weeks i will have it tested. engine all the plugs look clean 6 to 1

uncljohn Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/03/2013 Location: Peoria AZ Status: Offline Points: 5394	Post Options Post Reply Quote uncljohn Report Post Thanks(0) Quote Reply Posted: May/21/2015 at 1:14am
	It sounds like you are going a proper direction. However a compression test may add additional information that may help you out. And they are not that hard to do.
	70 390 5spd Donohue 74 Hornet In restoration 76 Hornet, 5.7L Mercury Marine Power 80 Fuel Injected I6 Spirit 74 232 I-6, 4bbl, 270HL Isky Cam

gird123 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2015 Location: Nevada Status: Offline Points: 45	Post Options Post Reply Quote gird123 Report Post Thanks(0) Quote Reply Posted: May/21/2015 at 9:12am
	i started pulling it apart last night. I should do the compression test, but I convinced my self the time i have in to the compression test i could have it apart and i have never taken a head off before. I'm going to have the head tested($25 to have it tested). If it is ok i will reinstall. If not i'm looking into the 4.0 swap. Looks like i can get a used 4.0 head with exhaust manifold for 100. Then i would just leave it carbureted for now. Edited by gird123 - May/21/2015 at 9:17am

gird123 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2015 Location: Nevada Status: Offline Points: 45	Post Options Post Reply Quote gird123 Report Post Thanks(0) Quote Reply Posted: May/21/2015 at 7:27pm
	So I did a compression test, warmed it up for about 30 min: 1=129 2=130 3=126 4=130 5=137 miss read that. number five is 137? 6=132 Did I mention it runs great. I pulled and tested the tstat again. I don't know what to do? Edited by gird123 - May/22/2015 at 10:55am

vinny Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Jan/05/2012 Location: Calgary Status: Offline Points: 2837	Post Options Post Reply Quote vinny Report Post Thanks(0) Quote Reply Posted: May/21/2015 at 8:17pm
	How long does your cooling system hold pressure after you shut it off? I think there is a way of testing it with a pump but I have never seen one. No oil contamination? The compression test looks good.

gird123 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2015 Location: Nevada Status: Offline Points: 45	Post Options Post Reply Quote gird123 Report Post Thanks(0) Quote Reply Posted: May/21/2015 at 8:23pm
	no oil that i could see.

gird123 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2015 Location: Nevada Status: Offline Points: 45	Post Options Post Reply Quote gird123 Report Post Thanks(0) Quote Reply Posted: May/22/2015 at 11:10am
	I went back and looked at my picks again and the number 5 is high? Any thoughts what i should try next? Should i pull the head?

tyrodtom Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6212	Post Options Post Reply Quote tyrodtom Report Post Thanks(0) Quote Reply Posted: May/22/2015 at 1:19pm
	Is your radiator top tank higher, or lower, than the topmost part of the engines cooling system ? If the cooling passages in the head is higher than the top tank, just filling the coolant to the top of the radiator isn't filling the head, you've got a air bubble in the cooling system. A AMC 6 is taller than the 170-299 cid Ford 6 that came in the Bronco origionally. You need to put a bleeder in the thermostat housing, or jack the front of the vehicle way up in the air when you add coolant. Some sleek cars have a coolant set up that the radiator filler isn't the highest point in the cooling system, they are usually equipped with bleeder valves at the highest point in the system, to get rid of the air bubble at the high point, or you can jack their front ends high until the radiator filler becomes the high point. That might be your problem created from a AMC 6 in a Bronco, with a Toyota radiator.
	66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.

gird123 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2015 Location: Nevada Status: Offline Points: 45	Post Options Post Reply Quote gird123 Report Post Thanks(0) Quote Reply Posted: May/23/2015 at 9:52am
	The radiator appears to be the highest. It would be easy to move it up a little.

tyrodtom Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6212	Post Options Post Reply Quote tyrodtom Report Post Thanks(0) Quote Reply Posted: May/23/2015 at 11:45am
	You've had two indications the gasket, and the head is good. The compression test, and what you called the block test, but I assume was a combustion gas test. The fluid from the test kit turns yellow if there is combustion products in the coolant, it can't tell you where it's from, it can be a cracked head, cracked block, or blown gasket. But from my experience it's better for finding very small combustion leaks than a compression gauge, but it won't tell you where the leak is. There is a very time intensive way to use it to isolate what cylinder is leaking, but it takes a lot of time. But with those two test you've pretty much eliminated the possibility that it's a head gasket, or cracked head/block. But you've never said if you've done a cooling system pressure check. If your cap or cooling system isn't holding pressure, even 40/60 antifreeze mix will boil at less than 230. Or if you've got a air bubble in the system, it's going to try to stay in the highest point in the cooling system. You can eliminate it by jacking the front end high in the air, then filling the radiator slowly.
	66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.