hey yall im really stumped here. I have a 1990 firebird with a 5.0 TPI 5 speed and ive had some real bad overheating lately. I have a 160* thermostat and ive had the car for 3 years now and ive never ever had a problem with over heating, i live in utah so even during the summers when the air 100* ouside my car could still keeps temp at 160*. lately i noticed that the temperature will steadily continue to rise and it got to 260* before i shut it off and determined that somethung is wrong. I went ahead and replaced the radiator along with new coolant at a 50/50 ratio, replaced the coolant overflow reservoir, the thermostat, and i replaced the water pump 2 years ago and it still seems to be in good condition. there is no noise coming from the water pump, and there is no play in the shafts. AND IT HAS NOT MADE ANY DIFFERENCE AT ALL. it has always had 2 electronic fans, i know one of them is almost always running, i dont know when the second fan should be turning on. The air dam isnt in perfect condition but its pretty much all there and its never been a problem. I know that the coolant temp sensor is accurate because that is also new and there was much heat that is warped my intake duct and the upper and lower radiator hoses and swelling up quite a bit (which also leads me to belive that the water bump is creating pressure as well as water flowing between the radiator and the block)

The overheating will continue to rise slowly as im driving and idling, at freeway speeds it will slow the increase of the temperature a little bit, but it still will not bring down the temperatures.

SO! what do i do? i thought ive looked at every aspect of the cooling system. Is there something that i missed? any help would be great, i usually do pretty good but this is one of those things that just has me stumped! I really do appreciate and all inputs.

 

Check timing and fuel psi.
compression/ leak down
Fans old? Turning slower than normal?

 

50/50 might be too rich a mixture, for heat dissipation. Check the protection chart on your coolant container. You might be able to run 70% water, 30% Antifreeze.


You should buy a "Block Check" chemical dye test kit. The dye changes from blue to orange/yellow if it detects "Combustion products" (exhaust, blown head gasket, cracked head, etc) in the cooling system.

https://www.harborfreight.com/combus...tor-64814.html

 

Are both of your fans coming on?

 

The coolant temp sensor being new doe snot mean it is accurate. aftermarket IR temp gun is a good way to double check

 

Have you checked to see if your heater core is flowing well? It could be clogged up and not flowing water. Easiest way to tell is to bypass it.
Also, does the second fan come on when you turn on your AC? I believe it should come in immediately.

 

ive always ran 50/50 and it’s never been an issue. I’ll go ahead and run 70/30 see if that does anything

 

may friend used an IR gun there is now doubt that the temp sensor is accurate

 

I don’t know when they are supposed to both be on. I know for sure that one of them is usually running

 

ill go ahead and check my heater core again, but as far as I can tell it’s perfectly fine, the heater blows really hot and I’ve flushed it not long ago.

 

Make sure it will cover your lowest ambient temp winter needs. Otherwise, water conducts heat better than the ethaline glycol antifreeze, our older cars call for.

 

I replaced the entire ignition and fuel system, every single component and now the engine runs like a dream, the timing and fuel psi is great. I haven’t done a compression test in a few months, last time it was good. How does the compression leak down affect my high temps?

 

Your gauge may be off. Id check that out as well

 

If I recall... 91.. .

1 fan comes on when coolant reaches, I think 220 and is controlled by the ECM using the coolant temp sensor in the front of the inake manifold....., then the second comes on at like 240 / is activated by the sensor on the passenger head.

Both should come on when the ac is turned on.

 

You replaced everything EXCEPT the radiator cap.

 

yes, check radiator cap. Also a sbc has a coolant bypass port so if the heater core was blocked I don’t think that would make any difference. Blown head gasket could cause overheating. But firstly I would check it with a mechanical gauge.

 

Maybe you got a bad thermostat...

 

What about the lower hose having no spring in it?

And this might have already been mentioned, but wrong rotation water pump.

 

First of all the radiator cap was already new. Secondly I replaced the entire radiator that came with a new cap and still made zero difference

 

What am I checking with a mechanical gauge? Also I see that head gaskets could be a problem, however the oil and coolant are both clean, no contamination at all, Al my exhaust is clean too, no smoke or anything coming from my exhaust. So I’m under the impression that my head gaskets are okay

 

like I said. I raplaced my thermostat and nothing changed

 

could you explain more about the lower hose? Also the water pump has been on there for a couple years and has been fine so I don’t think the rotation could just randomly change

 

Yes those are GOOD signs, but not enough to rule out combustion products in the coolant, as the cause of overheating. Head gasket, warped/cracked head (or, less likely block) failure sometime allows combustion gasses to leak into the cooling system, yet not have oil and coolant mix.

 

The lower radiator hose should have a spring that keeps the hose from collapsing. The suction created by a properly working pump can flatten the hose, cutting off the coolant flow, especially when the coolant is HOT.

Both the v-belt and multi-ribbed water pumps look the same from the outside, but their impellers are different. Looking from the front of the engine, the v-belt rotates the WP's shaft CW and the multi-ribbed turns CCW. I don't know which setup you have, but if multi-ribbed or "serpentine", could the belt be on the wrong side of the pulley?

 

Right about the SPRING in the lower hose. I started in the Auto Repair Business in 1973. At that time every new lower hose, came with an inserted spring. Now, not so much. I do not, off hand, recall buying a lower radiator hose that included the spring. I just bought a Delco 88908823, lower Rad hose, for my 1979 (403 Olds) Trans Am. NO spring. Some have opined that the higher pressure of "modern" cars prevents the lower hose from collapsing, at higher engine/vehicle speed. I am NOT sure about that. Pump volume (at higher speed) is pump volume.

 

My replacement lower hose did not come with a spring. What's up with that? And how would I remedy that situation?...

 

https://www.ebay.com/itm/333292633636?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=333292633636&targetid=1645685073568&device=c&mktype=pla&googleloc=9029965&poi=&campaignid=20133407470&mkgroupid=147476396765&rlsatarget=aud-1315132079729la-1645685073568&abcId=9312979&merchantid=131376503&gclid=CjwKCAjwxaanBhBQEiwA84TVXDMhbvjfJzXOp7htnXO-6LL_O38foXizQPsb7eVtZoDue2y_MHWSdBoC6BEQAvD_BwE

Pretty pricy! I might search some spring manufacturers, for a generic, plated ,spring, the right size.


https://www.inlinetube.com/products/...BoC5oYQAvD_BwE

Much better deal!

 

Here is a couple that I found:
1955-1988 GM Cars Lower Radiator Coolant Hose Inner Support Spring 17" Long EA | eBay TOO expensive.

But easy to find for Mustangs: (and stainless steel)
Mustang Lower Radiator Hose Spring Stainless Steel Small Block 1965-1973 (cjponyparts.com)

 

i know what you’re talking about. I’ll have to pick up the kit and give it a try

 

Harbor Freight has the kit, probably Amazon and others.

You gonna want an approx. 5" long piece of 3/4" (I believe) PVC Pipe, or a correct size PCV "Coupler". This goes between the base of the tool and the radiator neck. Because the water return to the radiator flows just below the neck. You must not suck up coolant, just the vapors. Liquid coolant will give a False Positive test result. Eyeball the filler neck and get something at H , Lowes, ACE, etc. Good Luck.

 

I ordered below from ebay. $ 7.20 w/ free shipping. I think it will work . I will advise its dimensions, after Sept 12 when it arrives,

https://www.ebay.com/itm/16341266480...-desc-maincntr

 

As simple as it is to remove the water pump, you may want to swap it out. It's possible the impeller is slipping on the shaft. If you want to confirm, you can remove the impeller cover and see if the impeller will spin with the pulley stationary. Aftermarket parts or factory plastic impellers are notorious for this over time.

 

thanks for this. I have a strong feeling you’re on to something. I will go ahead and pull it off

 

On dodge magnum motors, I've seen the impeller sides worn completely off and the water pump surface shot-peened. Gm 60* V6 were notorious for the impeller splitting and the shaft spinning independently, with no noise or play to tell you anything was wrong.
I worked a cab company as a mechanic years ago that used GM minivans in their fleet. The stupid things I've seen still give me nightmares lol

Please update with what you find.

 

Please keep us posted 🙏

I have a 92 Z28, and I have the exact same issue as op. I had a LOT of mods done including the cooling system.
*Three core aluminum radiator
*TB bypass
*90's Ford Taurus fan with shroud
*Royal Purple Ice
*40/60 mix
*Lives in AZ

 

Your temp sensor in the intake is just for the gauge. Replace the fan switch in the pass side head. Mine was overheating and the fan switch connector was melted apart. Also check your fuel pressure. Running lean can cause overheating. As others have said, check temps with an IR temp gun.

 

I took out my 195° thermo and put in a 160° thermo with a new gasket this evening. So I will see how she'll do tomorrow when I go to work.

Questions: If the waterpump direction is wrong how fast would it overheat? Mine is on the left of the pulley (reverse)...

Is there a common rotation or is that only for certain years?

The pulley/studs are swapped out when you replace the water pump so it could be ribbed or flat but I never done the water pump so who knows it its the correct pulley...

Why would Chevy do this to us UGH!

 

Not a good idea. Put the right one back. Fix whatever ails the car instead of jacklegging it.

Exactly what is your problem? Exactly WHEN did whatever problem you're having start?

Yes a 92 Z28 should have the "reverse rotation" (counterclockwise) WP.

Rotation direction is SIMPLE

If the INSIDE surface of the belt goes over the pulley, it rotates the SAME direction as the engine (clockwise viewed from the front).

If the OUTSIDE (back) of the belt goes over the pulley, it rotates the OPPOSITE direction from the engine (counterclockwise).

The impeller inside the pump is designed to move water in only one way. I also have seen them ate up by all sorts of things; cavitation, corrosion, etc. It's not as common as it used to be though.

"Chevy" didn't "do this to us". It's simple geometry. ALL cars with serpentine (snake-like) belt systems turn some things CCW. The WP is probably the most common one to see this way on cars in general, aside from idlers & tensioners, since its power demand is less than the other accessories. AC, PS, & alternator generally turn the same way as the crankshaft and have the belt wrapped around the pulleys a greater amount than the WP usually, for preventing slippage on them. The advantages of the "serpentine" design include lower power losses, no "adjustment" required (the tensioning system is automatic), and a much stronger belt.

Chevy V8s changed over from V-belts (and for a couple of years flat ribbed belts that worked the same way, looked alot like "serpentine" ones but aren't "snake-like") that all drove everything clockwise, to "serpentine" systems, in around 87 - 88 in various chassis and engines. So that's the approximate date for the WP changeover in our cars as well. Some engines got it in 87, some in 88.

Hard to say... like, how long is a road? It would depend on the outside temp, what the car is doing, etc. But, usually, pretty quick; most cars get up to operating temperature in maybe 3 - 5 minutes, and if the WP isn't working (which is pretty much what happens when it's being turned backwards) it'll overheat a minute or 2 later.

The spring in the lower rad hose isn't as necessary today as it used to be. Since there's supposed to be 16 psi or so of pressure inside it, it doesn't tend to "collapse" like it did back in the early-mid 1900s. Still a good idea to be sure, but rarely a failure point.

 

I would compromise and use a "High Flow" 180* T-Stat. I have, on my older vehicles, for decades with good results. I know 192-195* or whatever OE is "correct", but with OLD head gaskets, castings etc. , I like the 180*. I even passed Cali's horrible SMOG teats, w/ 180* Stats.

My 2 cents worth.

 

I get what your saying and not jacklegging it. Just testing as I've heard other use a 160° tstat. I do live in AZ so just testing.

So wp is fine, I did install the spring in the lower with a new lower radiator hose. It takes about 20min to get over 220° it will go down from 240 when I'm at a stop, under throttle it goes up no matter what fast slow or freeway. It does have a stock tune so maybe thats my issue?

The following is what I've done to the motor;

*Edelbrock performer aluminum heads
*Scorpion 1.6 roller rockers
*Sanderson shorty headers 1 7/8" to 3" collector
*3in pipe 2-1-2 to a trick flow muffler with rectangle tips
*Emissions delete
*58mm BBK TB to a SLP intake setup (runners and plenum - partially simeased)
*Walbro 255lph fuel pump
*30lb injectors

I will put the Lil Chubbs cam in it soon. Maybe its just running lean thats causing the heat? This week Friday I'll be ordering a stage 3 prom from HAWKS.

I appreciate the help and definitely take the criticism with respect and understanding.

 

It always ran warmer then usual but it was after the build is when she started getting hott. My Juliet is not heat happy, but damn she runs great.

 

@MarksmanB what happened? Did you fix it and if so, what was it?
Your car's problem sounds identical to my car right now and I am losing my mind.

 

If it is a Firebird, put an Iroc Z lower radiator scoop on it. These cars need a large scoop under the radiator to divert airflow into the radiator stay to cool at highway speeds. Without it, the car will overheat at highway speeds. The Camaro lower air dam is taller, catches more air and also creates more of a low pressure area behind the radiator to help draw the hot air out of the engine compartment.

https://www.ebay.com/itm/29636177339...hoC5zwQAvD_BwE