Hello.
Looking for some help with a cooling problem.
Have a 72' 350/200 motor. Had an aftermarket water temp gauge, not electric. Was reading approx 190 consistantly until I drained the coolant to replace the temp sending unit back to factory original so I could use the stock gauge that was in the car. re-filled system with the same coolant that was drained out and started car and noticed temp creeping past 210, 220 250 until I shut it down at 260 or so, and had a boil over out of the overflow of the supply tank. Upon temp creeping up, I would see a stair step effect on the temp gauge; 210 back to 190, back up to 230, back down to 200, back up to 250 etc..
Took a cooking thermometer and measured temp at supply tank and was very close to was either gauge was reading. Overheat will occur every time, if I let temp continue to rise, which I dont want to continue doing.
Thought this may have been air pockets. Based on my forum readings I have done the following:
1) raised car on jack and filled system and ran engine with supply tank cap off to get rid of air pockets. coolant level in tank at completion seems to stay at same level once car has cooled down and no more bubbles
2) no milky or engine coolant in heads or oil.
3) no coolant out exhaust.
4) thermostat was stuck open fixed this and operates correctly but not cause of problem.
5) re-installed the aftermarket gauge and has same problem as factory original(although this is the gauge that read consistant 190 degrees, and car never overheated.)
6) checked radiator and is hot on the left side where coolant enters and gradually cools as I checked it to the right from top to bottom where coolant exits.
7) ran without thermostat and same overheat problem.
8) left thermostat housing and hose off and ran car and intake filled up with coolant so I have to believe that water pump is working.
9) flushed radiator with garden hose and water to check flow through radiator and flow seemed to be okay.
10) Used a house fan to help with radiator heat removal and still overheat. Thought radiator is functioning fine before this test.
11) Ran vaccum advance directly to rear intake manifold connect and still overheat.
12) checked upper and lower radiator hoses after overheat or when I shut down at a high temp condition, and they both seem highly perssurized, although I can squeeze them. I also hear bubbling in the thermostat area of the intake manifold at overheat or high temp.
13) Overheat/temp building occurs at idle after 7 to 10 minutes for a cool engine, and in the same amount of time when driving from startup of cool engine.
14) replaced coolant with straight antifreeze and still overheated.
The overheat problem only started after I drained the coolant to install a new temperature sending unit, and then refilled coolant and started engine. Im either missing something, or caused something with this change. Any help would be greatly appreciated.
Thanks!
Harry

 

Long shot here. If you were to pull the t-stat, refill with just water, and run with the cap off........ just for a short while. Does it look like the water/coolant is flowing at a good pace?

Just wondering if something has blocked the flow.

 

don't no what your problem is, but if you run straight antifreeze it will be alot worse. you need water in there to take the heat away.

 

I can try this, however I have a hard time determining flow since there is no way to visually see flow.(dont have pressure tester or anything.)
This is why I pulled tstat and housing and ran engine with antifreeze. I visually checked the intake opening where the tstat was and sure looked like the antifreeze filled up intake quickly and fully. Reving engine caused it to overflow onto intake a bit. As for the radiator, I pulled the upper and lower hoses and shot water thru the upper hose and it was coming out of the bottom hose pretty strong but like a shower head, in that it was coming out around the outer edges of the lower hose. I thought this was okay since the tubes in the radiator are very small so coming out like water out of a garden hose wouldnt make much sense.

 

When I originally refilled, I used the 50/50 mix that was drained out. I did this since motor was rebuilt about 4 months ago and new mix put in before I got her from previous owner.
Remember, everything was fine until I replaced that stupid sending unit to make the factory gauge work. I know the sensor has nothing to do with it. I thought I may have had a bunch of air pockets when I drove it after the refill and new sending unit and maybe this caused a head gasket to blow, but I dont see any symtoms of this; only continual temperature rise in a stair step fashion until temp gets way to high.(250 260). Maybe I missed some of the tell tale signs of head gasket or blown head.(I used the forum blogs to verify head/head gasket problem, thus the long troubleshooting list)
I refill with 50/50 and test, and if you can refresh me on some of the tell tale signs of blown head gasket/heads, Ill see if I missed anything.
Thanks

 

harryakc..... When I meant to refill with just water to check the flow (w/o tstat), I should have also mentioned you'd do this with only filling the radiator to 2" low, then you would see the water moving.....with-cap-off. (only while the engine is still cold, only for a minute or so).

As for blown gasket, it could be possible to see bubbles in the overflow tank when the engine has reached a higher temp to attempt a purge of not just fluid, but now air. (but you already said no smoke, and I'd think just as you could force compressed air out into the water stream, you would suck it back in and out the pipes). Another "sign" would be a rock-hard upper radiator hose. (right, because that now has some pretty high pressure in it).

Another way to check for a blown gasket is exaust temps at each manifold exit. (you'd need a small RayTek infrared unit or sorts for that). Easy to spot when water is cooling out the exhaust, and at which port because the temp is WAY lower......I mean you will see 300-400+ at the good ones, and something in the 200's for the exhaust port/cylinder that has a problem. (and that I've seen happen with cars that had a rebuild and needed the heads decked a smidge).... it was just enough in one area to cause an issue.

........... but, is it a pain to try the water flow idea?

 

Im still a little confused. Where am I looking to see the water flow?
I have my cap installed on the harrison overflow tank. I have already pulled tstat housing and hose off and ran engine with coolant and looked through the housing opening in the intake and can see strong flow of coolant, so I know pump is okay. Just cant know how to visually check good flow through radiator. Unless you mean to put 2" in and leave lower hose on and check intake manifold at tstat housing and check flow. I just thought I really did that also when I did the pump check above.
BTW, I thought the top and bottom hoses were pretty rock hard at the high temp condition, although I was able to squeeze them with a lot of force.
Also, would the gasket problem you described get picked up on a compression test?(Im thinking maybe not but let me know.)
Do you have a good coolant flush/cleaning procedure to make sure I dont have blockage?
Thanks in advance for the help!

 

Fill Rad. about 1/2 way with water. (Or drain 1/2 of what's in there out). Reason to have 1/2 full is so you can see the top row of coils in the rad. This will let you know if the rad. is stopped up.

Take T'stat off, put housing back on.

Open rad. cap and leave off. Start car, and look down the rad. cap opening. It will be obvious if you have good flow.

Basically, if you have good flow, it's not the rad., but something else. My guess is when you drain the system, you rad. got clogged up, especially if it's an old one.

Most heat problems relate back to improper rad. flow, (ie: old radiators), back water pumps, or bad fan clutches.

Good luck.

 

NEVER run an engine with straight antifreeze. Water is basically the best coolant you can use. The green stuff you pour in there is an ADDITIVE meant to keep the water from freezing. It really has very little cooling benefit. I have heard of people thinking that if 50/50 antifreeze to water is good then 100% antifreeze would be better.

Their burned up engines tend to differ...

 

Unfortunately, This is what I wanted to do long ago, but my rad cap is on the external overflow supply tank. There is no way to view the flow through the rad other than removing the lower and upper hoses and shooting water with a hose through to and seeing how much and how fast it comes out of the bottom. When I did this I used a garden hose and fed water into the top hose, and watched flow and volume coming out of the bottom hose. The flow out appeared to be pretty strong, but not gushing out.

 

Simple answer and response........How old is the Radiator? If it's over 15-20 yrs old, junk it. So many folks chase overheating ghosts, when it's simply an inadequate performing radiator. (ask me how I know.)

 

Yes, to work and be effective, coolant must be mixed with water (ideal at 50/50 to 70/30 mix - prior figure being coolant). Drain the system completely (drain ****, lower radiator hose, etc.). Pour half a gallon of coolant in your radiator followed by half of a gallon jug of distilled water (cheap at your local grocer). Then add the remaining half gallon of distilled water to your half-full gallon of coolant and you have a 50/50 mix to finish filling it. Do the same with another gallon of coolant and distilled water and you should have more than enough. The leftover is already a 50/50mix for when you need to top it off. This is how I do it, others may have other ideas.

 

So why not just pour in a gallon of each to start with, and just finish off with a mix? Me so confused........

 

Radiator cap bad, had exact problem with 3/4 ton GMC pickup.

 

Kaamacat,
Ran with straight water when flushing system and useing either water temp gauge, and temp never got over 130 and ran engine for 5 to 10 minutes until it flushed clear. I left the top hose off the radiator when I did this. It was the same with or without the tstat installed. I also noticed a cavitation of water flow out of the top hose coming from the tstat housing. Bursts of water/coolant followed by nothing. This went on until I shut it down when flush was complete. Is this normal flow? As a side note, When I leave rad cap off the external supply tank and I get upwards of 240 deg. I can see coolant backing up and bubbling in the tank until it overflows. As well, with cap off or on when I reach overheat, upper and lower hoses are hard as rocks, like some sort of pressure build up and the rad feels hot all around. Seems like my boiling point is being reached and thus the cause for the rock hard hoses?
What about the bursty flow when flushing? Could be because water pump is pumping more than flow coming the the garden hose I flush with. Could there be any other flow issues that I should look for?
Also checked fan clutch after overheat shutdown. Can move it with resistance. When I try to spin it it just stops when I let go. Some other threads indicate should be really hard to turn. Mine is as described.
Anyone chime in here. I will always take good advice.
PS. New rad cap...no difference. New 50/50 mix...no difference. Air pockets...Think I got them. Jacked up car, ran engine with cap off to burp...any other ideas here or things I missed to ensure no air in system would be much abliged. As for new rad. It looks like original, and things seem to point this way to me, but what would cause its coolant capabilities to fail just after draining coolant to put new temp sending unit in?
harryakc

Harryakc

 

I had similar promblems cooling my 70 finally i replaced thae radiator and promblem was solved.

 

It's funny how folks will chase heating ghost's, isn't it? I did the same.........replace the old antique radiator and be done with it. Of course you never answered my questions, so don't know what to tell ya..........hint.......you want help? Answer the questions........

 

MSvetteman,
I thought I did respond to your questions in past threads, but Im no expert with the forum thread responses. Sometimes they're mixed in with other peoples responses.
My 72' setup doesnt have a rad cap on radiator. Cap in on the expansion/supply tank. So filling rad with 2" in water and looking down rad through rad cap opening to see flow isnt possible. Thats why I originally took top hose off at tstat housing and shot water down hose into radiator with bottom hose off and checked flow that way. Water came out and I thought flow was okay but what is okay? Can you give a description of what a good flow out of the bottom would be or another method of determining flow with my setup?
Also, I cant say for sure, but rad could be original harrison aluminum, or a recore. It has the oroginal gm part# and 72' date code with the harrison warning sticker on top.
I also heated engine up to about when coolant would start to boil, shutdown engine and checked fan clutch. There was resistance to the point that I could move fan by hand, but if I tried to spin fan it would stop as soon as I let go of it. Everything seemed the same as I just described when engine was cold.
Flushing system with cold water and engine running, the gauge didnt budge off 130 deg., so to be engine flow seems to be okay. I dont have an I.R. gun, but am looking to either borrow one or get one. Im no expert here, but not a novice either. Somewhere in between and can always learn a thing or two from the forum pros. Anything you can help me with is appreciated.
Harryakc

 

Harry, save yourself a lot of time and grief, and buy a good Dewitts direct fit replacement radiator. If that rad. is an original '72 rad, that makes that antique 34 years old.......I would ditch it in a heartbeat. If you ran the system without a t'stat, and it still overheated, you have serious circulation problem and the rad. isn't doing it's job.

good luck........

Also.......how long had it been since the rad. had been flushed? You have a strange problem.....main reason I think it's the rad. is because still overheats without the t'stat in.....and with the system closed, it overheats. That, or you have a serious air trap problem. I would at least eliminate the radiator, and also that will get you into the 21st century.

 

Yeah, I agree about the rad replacement. It's just so weird that it was running great at about 190 deg. before I drained and replaced the sending unit. As well, I just want to be real certain its the rad before I dish out 500.00 to 700.00 bucks.
Thanks,
Harryakc