Problems with coolant system in my 1986 Gmc Sierra

[king foid]

Long post warning
I have been having an issue with the coolant system in my truck since day 1 of firing the motor. The motor i have in it now is a 400 small block, which replaced the 350 that was originally in the truck. The truck is ac also. I'll start from the beginning to better explain my troubles.

In May i swapped in a rebuilt motor for my truck, after I had spent over a year restoring it. Before i pulled the motor out, the heat and coolant system worked fine, no problems. When we fired the motor, the motor builder was present. With the radiator cap off idling the truck, water would shoot out of the radiator cap 2 feet. He said that the motor was just being stubborn and that there were air bubble somewhere.

The first few test drives, i noticed that my truck would constantly bounce around in temperature, being 180 degrees one moment, 220 degrees 5 seconds later, and then back to 180 another 5 seconds. I talked to multiple people, and they said to relocate the temperature gauge sending unit to the manifold, instead of block. The truck stopped bouncing around in temperatures and stayed at 180 after that, meaning that the truck wasn't showing the correct temperature.

As the seasons started to change, I noticed that i had no heat in my truck, and that I can hear a thumping noise coming from the motor when i shut it off. When i run the truck without a radiator cap, once i shut it off water will shoot out into the air. I thought that i had a blockage in the radiator causing it, because the radiator was all corroded. After changing the radiator, and 3 thermostats the truck is still making noise and puking antifreeze. When i start the motor, it will warm up normally, and once it reaches 180 degrees, it will shoot water into the overfill tank. Also, when the thermostat opens, the radiator hoses are all relatively soft, they feel like they have no water flowing through them, to the point where i can completely restrict them with my hand. The heater hoses are not hot at all going into the cab, and they also feel like no water is circulating. The truck does not overheat whenever this happens, it stays at around 150 degrees. The thermostat also makes a clicking noise when it opens sometimes, and the radiator hose feels like it is chugging for water. I also changed the oil 3 times over the summer, and there was never any antifreeze in the oil, nor does the exhaust smoke white.

I have ran the truck with out a thermostat, and it did not do any of these problems, but it also didn't get up to operating temperature because it was constantly circulating. I have changed the thermostat 3 times, and even checked them in 180 degree water to make sure they worked. In addition, i bought a funnel that locks onto the radiator to try and bleed the system for any air bubbles. When i do this, the radiator burps up bubbles, but does not take in any antifreeze like it should. All hoses are brand new, and the clamps are properly tightened. I have also disconnected the heater hoses and bled the system for air, but this didn't help either.

Can anyone help me troubleshoot, this problem, at this point I'm ready to pull the heads off and check the head gaskets?

 

[77 K20]

How did you route your heater hoses? Intake manifold to heater core to radiator? Or there is some other method of water pump thru heater core to manifold.

Have you pulled a heater hose to verify circulation? Or have you tried to verify you can get flow thru your heater core (hook up a garden hose or something to it).

You said it is a 400. Did the heads get steam holes drilled into them? What type of heads are they (vortec heads?)

 

[Georgeb]

Also need to check where the coolant restrictors are in the intake gaskets. I believe they should be located in the rear ports. A jumpy temp guage could indicate steam forming in the block.

 

[Fastereddie]

Wrong rotation water pump??

 

[king foid]

Thank you for the responses so far,

I have the heater houses routed so the upper hose goes to the upper hose goes to the radiator and the lower hose goes to the water pump. Water flows from intake manifold to heater core to radiator.

I took the water pump off and it spins clockwise. I read that these year trucks would have came with a counterclockwise serpentine water pump from the factory. This motor is out of a 72 chevelle station wagon, so I don't see how it would make any difference. I have the water pump running on a v drive system like the previous motor, and the previous motor had no coolant system or heating problems.

I took both heater hoses off and ran a garden hose through, and it was not blocked, nor did any gunk flow out through the hoses. Also, I don't smell any antifreeze in the cab, so I don't think the heater core is leaking.

I took of the heater hose going to the radiator, and no water came out.

The heads are stock heads off a 400 small block that have been completely rebuilt, new valves guides, and machining.

Should I pull off the intake manifold to see how the gaskets were put on?

Would not having steam holes drilled in the head gaskets have any effect? I'll ask my motor builder if he is positive he drilled holes in them just to be sure.

 

[CSFJ]

If the heads are originally 400 heads the steam holes will be there from the factory.

 

[Georgeb]

Regarding the heater hoses. The upper hose should go to the intake and the lower to either the radiator or water pump. That may be why you didnt get any water out of the lower hose. If you dont have flow through the heater core it will be full or air which will compress as the coolant expands and then blow coolant out like you decribe. Try changing that up and see what happens.

 

[chengny]

I have ran the truck with out a thermostat, and it did not do any of these problems, but it also didn't get up to operating temperature because it was constantly circulating. I have changed the thermostat 3 times, and even checked them in 180 degree water to make sure they worked.

Everything you report sounds like a textbook case of an inoperative t-stat. The geysers blasting from the radiator outlet tank, the gurgling/rumbling from deep within the block, the sharp temperature changes, etc - all usually point to a t-stat that is restricting flow from the engine to the radiator.

Have you tried modifying a thermostat to allow for better venting. It just involves drilling a couple of holes in the flange. You can start off with smaller holes than those pictured below and if that seems to help, make them a bit larger.

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You must be registered for see images attach

A thermostat needs to be in contact with a good flow hot liquid coolant to open fully and stay that way - steam won't do it.

Is it possible that even though the steam holes were drilled by the builder, they are slightly undersized or restricted by the head gaskets. If enough steam is generated - it will quickly migrate to the highest point in the system (i.e. the thermostat housing) and the operation of the t-stat will become sluggish. Increasing the area of the vent holes will help remove the steam (if there is any) from the actuating piston of the t-stat. Hot coolant will take it's place and the wax pellet will melt forcing the valve to open.

Just a thought - and a cheap easy solution to try.


Oh yeah, I firmly believe that when you figure out the reason for poor engine coolant circulation, the heater problem will disappear.

 

[king foid]

I miswrote, water flows from the water pump to the heatercore to radiator.

 

[Georgeb]

I miswrote, water flows from the water pump to the heatercore to radiator.

This is incorrect. It should be intake to heater core to either radiator or water pump as shown.

 

[chengny]

X2 - on that hose routing.

In a schematic sense, the suction side of the water pump (i.e. that plug where a heater hose can be connected) and the radiator are in exactly the same place. Essentially there will be no flow in either direction.

But George, even though I love you like a brother - I have to disagree with you on how the heater hoses should be connected to the core nipples.

In any shell & tube type heat exchanger, the flow of liquid should - whenever possible - be: in through the bottom and out from the top.

This arrangement does two things:

1. Since the liquid level has to completely pack the shell before it can exit out the top, it ensures that the shell is continuously being purged of any entrained air.

2. The tube surfaces receive the maximum amount of possible contact with the heating/cooling medium. If the flow was from the top down, it presents the possibility of "laning". IOW - the fluid could possibly just shoot right down the middle and never even contact much of the tube surfaces.

That is what your attached image shows as well.

 

[Georgeb]

X2 - on that hose routing.

In a schematic sense, the suction side of the water pump (i.e. that plug where a heater hose can be connected) and the radiator are in exactly the same place. IOW - there will be no flow in either direction.

But George, even though I love you like a brother - I have to disagree with you on how the heater hoses should be connected to the core nipples.

In any shell & tube type heat exchanger, the flow of liquid should - whenever possible - be in through the bottom and out from the top.

This arrangement does two things:

1. Since the liquid level has to completely pack the shell before it can exit out the top, it ensures that the shell is continuously being purged of any entrained air.

2. The tube surfaces receive the maximum amount of possible contact with the heating/cooling medium. If the flow was from the top down, it presents the possibility of "laning". IOW - the fluid could possibly just shoot right down the middle and never even contact much of the tube surfaces.

That is what your attached image shows as well.

You are correct and I should have cought my error being that I work for a manufacturer of shell and tube exchangers! Oops! I got lazy and didn't go look at my truck. I just did a google search and found that info but didn't verify it. Now I need something to wash down my humble pie.

 

[chengny]

Hah - please! At least you have the balls to admit to being overly helpful. When I show my ass, I just go offline and hide for a a week or so.

 

[Georgeb]

Hah - please! At least you have the balls to admit to being overly helpful. When I show my ass, I just go offline and hide for a a week or so.

Dad always said " If your wrong admit it. And if dealing with your wife and your right shut up."

Back to the problem at hand. If we get the heater hoses connected right and drill a hole or two in the thermostat this problem should be resolved.
Worth a try.....

 

[chengny]

If we get the heater hoses connected right and drill a hole or two in the thermostat this problem should be resolved.
Worth a try.....

For sure! Now that I understand how his cooling system is set up, I wouldn't even bother modifying the t-stat.

I miswrote, water flows from the water pump to the heatercore to radiator.

I am not familiar with engine modifications, but AFAIK the 406 CID motor is basically just a bored/stroked SBC - correct? Assuming that is true, and the water pump is a stock Delco type with the pipe plug located here (and the return from the core is connected as shown):

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And if the other heater hose is piped to the nipple at the top of the radiator's outlet tank like this:

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Even with the radiator full, when the engine is revved, the level in the tank drops to a point where the water pump starts sucking air and begins to cavitate.

At that point, the entire engine's normal coolant flow is disrupted and overheating occurs. And of course there is no coolant flow through the heater core.

The supply hose to the heater core must be piped to the top of the intake manifold. This area is on the discharge side of the water pump.

As long as that is piped correctly, it doesn't matter where the return hose goes. It can be connected to either the pipe plug at the pump suction eye or the radiator outlet tank - as noted above, they are schematically in the same place within the coolant system.