well i just bought this 84 z28 from some old man for $1000 mint condition with a few upgrades suchs as bigger heads, intake manifold, rebuilt and tuned carb by jba and flowmasters,shift kit and rebuilt motor.... anyways so when i drive my car on the freeway and get on it, it starts to over heat and overflows my overflow tank and i thought that my thermostat failed closed but its new according to the guy i have my air dam on my upper hose is new and my lower one feels solid could it be the thermostat, water pump, clogged radiator or hoses??? i also noticed the air temp sensor looks a little messed up does that have anything to do with it? also if im in the city it doesnt run hot or just cruisin on the freeway never goes pass 160ish which i think is weird only happens when i get on it on the freeway yeah some clown in a honda crx tried to race me and look what happend haha

Could be as simple as adjusting the timing. "Bigger heads" is a little concerning on a 305. Mixture might be leaning out with all those changes.

can take a look thanks any other ideas.... ????timing never crossed my mind...

Air deflector missing under the radiator, but I think you said that was in place.

yeah its still there.... its not in horrible condition either

well i ended up taking the thermostat completely out last night and hasnt over heated since so im thinking the thermostat just failed close

The old ones do fail closed. I wouldn't have guessed that given it didn't overheat idling. Cheap fix.

Might check your radiator cap as well. If the little center piece isn't spring loaded I always repalce them with one that is. Some times, if yours happens to have a heater return hose just below the fill neck & it doesn't have the spring loaded center, the rush of coolant through the htr hose can push the center open and push coolant out into the overflow reservoir thus running your system low on coolant. When you shut the car off and it cools down, the system will pull coolant back in and the rad will keep appearing full, even though it can still be giving you trouble when you drive it. Just a thought, good luck....

yeah well i took the thermostat out, new water pump, fixed the leak in the neck and tm im getting a new all aluminum radiator all because it really overheated on my way to the junk yard never before was there smoke comming from the engine till just yesterday and it would over heat after about 10-15min driving on the freeway im thinking its a headgasket now....although i checked the dipstick and didnt see any milkshake color but when i took my oil cap off i saw just the slightest bit of that milky color im gonna check the spark plugs next but please if anyone else can help that would be great!!! need all the help i can get

With it cooled down and the radiator full. Start the car up with the radiator cap off and watch for bubbling. Tiny bubbles like you see in a glass of pop (soda) floating around are normal, but anything bigger or actually breaking the surface and popping is sure sign of a head gasket problem. Watch it until it gets to operating temp.

Still curious what the "bigger heads" are on your 305. As factory heads go the stock ones on 305 F-bodies are pretty good given the small combustion chambers needed to keep compression.

well it turns out to be my intake manifold gasket.... and as for the bigger heads im not sure all he said was they are 197 and that was it.....im curious my self so i looked around for heads and couldnt find any he apparently had wrenched on
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and my mixture isnt leaning out its actually rich so im having my mechanic tune my carb for me..... not a big fan on toying with carbs haha

Great news. Pain in the butt, but not terribly expensive to fix. Sorry I wasn't any help.

I can't find any 197 head but there was a 3998997 used on '84 305's with a 76cc chamber. Our stock 416 heads (14014416) had 58cc chambers. Hope that's not what he meant by bigger heads. Would explain you running rich with such a low compression ratio. Still a great deal on the car for $1000!

I hate carbs too. Made a mess of mine. Five7kid finally bailed me out with a pre-tuned cc rochestor.

yeah all in all the car is great for $1000 its mint haha and as far as carbs go count me out i had to get rid of my old camaro because the carb needed to be rebuilt she just keept on flooding and it ended up vapor seizing on me but got rid of it =(

Yup this thread is staying alive unfortunately... well ok i took out the thermostat seeing its a myth that it cause overheating....i got a brand new 3 core all aluminum radiator... both hoses feel solid...brand new water pump..not a head gasket for sure...air dam is there....fan stays on constantly... and its still over heating i mean what else is there..? i noticed my oil pump is maxed out do u think there could be a blockage and no oil is getting to the engine? could something electrical be messing with it? i know my temp sensor is working right and my gauge is pretty accurate...i dont think the radiator cap could cause this it is a stant pressure release lever... SOOOO PLEASE HELP so i dont have to pay JBA $95 to diagnose the problem any input by anyone would be great common guys!!!! i dont want another camaro to end up on the side of the road and eventually in the can...

I think its a head gasket.... however there is no real yes/no test for the head gasket, the best indicators are the symptoms you can observe yourself.

A coolant gas test will pick up if the gasket is venting gas to coolant, but this is also shown by the system over pressurising and venting from the cap. The test can also give false +ve if the coolant has become contaminated.

A compression test likewise will only show a problem when it is already obvious from other symptoms. (its main function is to check valve and piston ring sealing)

A coolant pressure test may indicate a leak, but it won't tell you where it is unless you can see it.

The best indicators of a gasket problems are oil in coolant / coolant in oil / gas overpressurising the cooling system / external leaks or some combination of these.

Ray

Clogged catalytic converter?

hmmmm possible it is also backfiring im pretty sure my diverter valave and egr valve are shot

well if my cat was clogged would u be able to put your hand under the muffler and feel that theres no exhaust comming out? or..????

turns out it could be a faulty EGR valve... guess we will find out tm when i install it....

No, you are still going to feel some exhaust coming out or it wouldn't run. I don't have a way of checking it decisively. I can say if its clogged and you try to break in a camshaft. 10 minutes of 2000 RPM will have your exhaust manifolds glowing cherry red at night.

i can test that out tonight as well thanks...

Is the water pump for V-belt engines or serpentine set-up?

its a v-belt set up

so i finally got sick and took it in to diagnose it and sure enough its a head gasket so they say.... says engine failed chemical block test for hydro carbons... and they want $1655 to fix my problem.... =( so i guess im just gonna get rid of it cause i dont have the money and i dont know anyone who can fix it.... anyone from san diego willing to help?

That's too bad. Wish I was close enough to help in San Diego, getting tired of plowing snow and freezing.

damn thats miserable

ill take the car off your hands =] but that still sucks you should try some diffrent places you might find a better deal

if i had a book on it then yeah id do the head gasket myself but...i dont so i guess im just gonna get a mobile mechanic the hell with it..and he better not screw me either ill be pissed

Chilton book (not Haynes) is about $18. Hardest part is getting the exhaust manifolds loose. Did you ever find the casting number on the "bigger heads"?

nope i think im just gonna get new ones any ways whether the old ones are good or not anyone have a good idea on what size i should get?