Coolant system issue

[Uriel]

Okay, so my 79 k10 has a freshly built 350, new water pump, newish radiator and the thing starts up Fine. The problem is the temp gauge shoots up to overheat quick. So I shut it down and checked for leaking coolant. None that I could see. So I felt the top hose to see if it's hot. Nope, cold. When I squeeze the top hose, I can hear air coming out of the overflow nozzle under the radiator cap. It's a new cap, but seems like it's the wrong one because that nozzle shouldn't flow anything out unless the system gets over pressure. Also, the coolant in the radiator is still cold. The bottom radiator hose is hot, and the top one is cold. That just doesn't seem normal and I have no idea why it would do that unless the whole problem is the wrong cap. But even so, wouldn't coolant at least be flowing through the engine? Kinda lost here fellas (and ladies). Any ideas would be appreciated. Thanks.

 

[89Suburban]

If it is a freshly filled system it may have an air pocket stuck in the top of the motor. An air pocket can give a false reading on the gauge. Fill the radiator and your overflow tank, leave the radiator cap off, and let the engine run and warm up and open the thermostat and start cycling the coolant to run the air pockets out of it. Watch inside the radiator opening for the coolant level to drop when the thermostat kicks open, it will drop fast. Some coolant may spill out as the engine warms but it will drop real fast when that t-stat opens. You should also see coolant shooting into the radiator from the upper heater hose. When that level drops, top it off real fast and put the radiator cap on. Let the motor run a little bit and shut it off and let it cool down and draw coolant in from the overflow tank and it should be good to go. This is all assuming there is nothing wrong with your thermostat. You can also turn the heat on full blast in the cab if you are worried about it getting too hot during this process but it will take longer for the engine to warm up and open the thermostat.

 

[Uriel]

I'm not sure that the t stat ever even opened. The gauge pegged out but I'm almost positive it didn't open because nothing was going through the upper hose.

I do need to get a coolant reservoir though. That, along with the heater core, got broken when my brother and dad swapped out the engine. Once I get that stuff I'll try your suggestion. Maybe get a new t stat too.

 

[rainyraven]

^^ I would say get a new Thermo stat A.S.A.P 8 out of ten times they stick closed and then no coolant will enter the motor and then you have a hot motor

If you want to check to see if the thermo stat is sticking you can take it out.. put it in water and when the water starts to get hot enough you can watch the T stat open.. if the water starts to boil and the t stat does not move.. you know for sure its bad.

hope that helps ya

 

[89Suburban]

^^ I would say get a new Thermo stat A.S.A.P 8 out of ten times they stick closed and then no coolant will enter the motor and then you have a hot motor

If you want to check to see if the thermo stat is sticking you can take it out.. put it in water and when the water starts to get hot enough you can watch the T stat open.. if the water starts to boil and the t stat does not move.. you know for sure its bad.

hope that helps ya

Good tip, wouldn't hurt to try, easy to do, and peace of mind. Not expensive to replace either. Autozone sells aftermarket overflow bottles but if you can get your hands on a used factory one at the junkyard or even buy a factory one new I would recommend it over the AZ one, better quality.

Let us know how it goes.

 

[chengny]

Pull the t-stat out and leave it out for now. With no thermostat and after a warm up period, the dash gauge should read around 110-120 at idle.

Check for water pump function. Drain a quart or so out of the radiator - enough that there is an air space at the top in the end tank of the radiator.

Start the engine, and with the radiator cap removed, look down into the end tank. You should see streams of coolant flowing out of the ends of the crossflow tubes and dumping into the tank. Rev the engine and note whether the flow rate increases. If the water pump is putting out and the t-stat is removed, revving the motor should make the coolant flow increase.

While you are doing this test, feel the upper hose. It should be hot - but not uncomfortable to hold.

Warm upper hose (but not burning hot) and good coolant flow observed? Check your dash gauge.

Does it still read high? If so the issue is probably electrical in nature and you should start looking at temp indication as opposed to actual coolant temp.

Check the wiring leading up to the sender for a short to ground (dash gauges peg high when the sensing lead is grounded). If the wiring looks okay, try a new sender.

 

[Uriel]

Well, I fixed the cooling issue. Drilled a 1/8 inch hole in the thermostat flange and there must've been an air pocket behind the thermostat because now it cools just fine. Problem is, theres another problem.

I think I've got water and gunk in my gas tank. Timing is set to 8deg btdc and I'd I rev it, it backfires sometimes. Also, it was knocking no matter where I moved the distro, but after I pulled it out of the garage to park it, knock went away. My fuel filter is disgusting (see thru style) so I'm for sure going to change it. Before a few weeks ago this rig had been parked, not thinking for about 5 years (allegedly). How hard is it to clean out a gas tank? I'm guessing I need to drop it. Not looking forward to that...

 

[Chevyguy]

It's not hard drop one out. I used a floor jack with a piece of metal plate bolted to the saddle. You could also use a cut piece of plywood. Undo the straps and lower it down so that you can remove the lines from the sending unit, If they are original now is a good time to replace these lines. Don't forget to take the fill, and vent line hoses loose. If you have dual tanks I would do them both.

Clayton

 

[Uriel]

Well, I mostly got it fixed. I found out that the el crapo used radiator that my dad got, he didn't test before he installed it. All he did was spray paint it. no cleaning, no getting it checked out. nothing. he spent over 60 on it and its pretty corroded. now i haveto buy another one. AND the valves on clinders 3, 4 and 7 dont seal. now, heads gotta come off and valves getting lapped. but hey, at least i know what wrong with the cooling.

 

[Uriel]

Okay, oddly enough, I'm still having the issue of nearly no heat. First, I had the 5/8" hose coming from the water pump, and the 3/4" hose coming from the manifold. I was told that was wrong, so I switched the 3/4" to the water pump and the 5/8" to the manifold. When I did that I only got heat when the thermostat was open. So I moved the 5/8" to the water neck right after the thermostat. Now I'm getting NO heat and no fluid to the heater core. I'm thinking of moving the 3/4" to the manifold right before the thermostat, and the 5/8" staying right where it's at. I squeezed the heater hoses while the engine was running and they're only warm because they're inside the engine bay. There is no fluid runnning through them that I can feel. I'm kind of lost here, and cold because Michigan winter plus no heat = not an enjoyable ride...

 

[Uriel]

I'm an idiot. I figured out what the problem with no heat was. When I ripped out the original heater core, it was surrounded by this nasty, degraded stuffing type crap. So I pulled it all out and put the new heater core in there without replacing the padding. When the heater was on no air would go through the core, it would go all around it because there was gaps which had no resistance. Today I pulled it out again and noticed that, so I stuffed some rags on the sides of the core and taped them down with metallic duct tape. Now all the air is forced through the core and wouldn't ya know it, there's a crap ton of heat now! I wish I wouldn't have taken me so long to figure out, but hey, now I know. And I have heat!

 

[hinkv10]

I'm an idiot. I figured out what the problem with no heat was. When I ripped out the original heater core, it was surrounded by this nasty, degraded stuffing type crap. So I pulled it all out and put the new heater core in there without replacing the padding. When the heater was on no air would go through the core, it would go all around it because there was gaps which had no resistance. Today I pulled it out again and noticed that, so I stuffed some rags on the sides of the core and taped them down with metallic duct tape. Now all the air is forced through the core and wouldn't ya know it, there's a crap ton of heat now! I wish I wouldn't have taken me so long to figure out, but hey, now I know. And I have heat!

Has anyone else experienced this? I just finished replacing the heater core but haven't installed the heater hoses yet. I had a heck of a time getting the ac delete cover to fit and work and really don't want to take it off again. I am getting air out of the holes in the firewall where the two holes for the heater core pop through. Do I have to pull the heater core again?

 

[89Suburban]

Wow, I never realized there was supposed to be a seal around the heater core itself. I got to check that out on mine.

 

[hinkv10]

there is a seal on the firewall that goes over inlet/outlet for the heater core from the outside of the firewall. mine is degraded and helped slow down the air a bit. I'm going to hold off putting my heat together for the weekend to come up with a game plan.

 

[89Suburban]

Yah, I am aware of that one and that is another one that makes a HUGE difference. Some models you can also adjust the floor/defrost door to hit the windshield harder, and is yet another part that has a foam seal on it that falls off. At least looks like there is evidence of that, anyway.