Technical Slightly Hopped up 305 overheating...need some input.

Some very good suggestions here. I would check the water pump direction as mentioned. 305's are the ideal hotrod engines because they rarely run hot. I've run one in a 26 T tub and one in a 48 chevrolet pickup-both with mechanical fans and neither ever got hot. The pickup had a/c as well. A friend runs them in demo cars and says they will run 30 minutes after the radiator quits steaming. Good luck with the fix. You have a nice looking roadster.

 

a pusher and puller fan? dang. I would leave the puller fan. maybe get a higher cfm one. don't go 160 tstat. I live in LA and once it gets hot it will stay hot and not close up and give the water enough time to cool. I wouldnt rock anything less than a 180 in that car. every car I've bought the past owner always tried to "solve" overheating by using a lower tstat. it never helps when the weather is 90* outside.

 

Even if you think your radiator cover has "big holes", it is still probably blocking about 20 percent of the flow. Can you do without that 20 percent? Doesn't sound like it.

 

Creepy
I run either a 185 or a 195 year round here. it gets blue cold in the winter and hotter then the hubs of hell in the summer. the stat depends on the engine in question some of them run better cooler then hotter but that is a tuning deal more then most are willing to play with. Either temp is a good shot for an SBC.

 

I WOULDN'T DOUBT IT! It's always one thing after another, right?

All the hoses are a year or two old, so I think they will hold. I went out and swapped in the 160 thermostat and topped off with water, so it's much closer to 75/25 than it was. I started it up and let it run for about 15 minutes. It seemed to take longer to overheat, but in the end, it still did....doh. I also removed the grill shell and the fan I had on the front of the radiator. Same results. My next step is going to get one of the compression leak kits and see how that pans out. Chasing stuff like this is so annoying. If it ends up being the head gaskets, I'd wager that with my luck the heads are warped....at which point I'll pull that engine out and haul it off for scrap.

 

If you have good oil pressure and no noises why not look for a decent set of 305 heads? This has gotta be your problem if the timing and carb is set right. Remember old Chevys ran a small 4-blade fan and stayed cool.
Also make sure the radiator is flowing water well. Is the bottom hose collapsing?
If you must run an electric fan go to a salvage yard and buy the largest size that will fit with a shroud built on it.

 

The cooling system only sees pressure that the cap allows. Test the cap for its rating. Testing while hot is great because things move around.

Pressure testing the system at 35% more that the max pressure that is ever seen is horrible advice, actually worse than horrible- potentially damaging, dangerous, and expensive.

 

I had the radiator tested at the local shop, it tested out good...that being said, I have noticed the lower hose collapsed once or twice over the past several months.

Oil pressure...hmmm. It will start off around 60 and as it warms up settle around 35-40ish. However, yesterday on the way home from a quick run, I noticed it was around 25ish idling at the stop light, but promptly went to 40ish when i got up to speed.

 

That sounds normal and great. I forgot what year the engine is. I'm thinking a serpintene belt engine. Are you sure the water pump has been changed to a V-belt standard old style flow pump? A water pump is cheaper than a set of heads.

 

Are you doing your test driving or just sitting in the drive?

I'd replace the collapsing hose either way, I had one blow up and scare me pretty good

 

Last I recall, when I ran the numbers, early 90s? I looked for the pad on the front of the engine for any info telling me if the water pump was reverse rotation, but couldn't find anything...any ideas where else to look? The pulleys on the engine are entirely V-belts...that's not to say the PO didn't swap out the pump, use V pulleys, and not realize why his motor was overheating and thus sold it to me. It's entirely possible! Would it be feasible, as a test only, to run the flat back of the belt *under* the water pump instead of *over* it to see how it behaves? Idling, that is....

I've tested it both ways...driving and idling in the driveway/garage (yes, with the garage door open!)

Update: I rented the compression leak test tool over at AutoZone...with the blue fluid....and happy to report that the fluid did *not* turn yellow. Doesn't mean I don't have a blown head gasket, but it staying blue and no milkshake in the oil is good at least!

 

What did you do with your heater hoses? Some engines like to have that by pass loop.

Does it run good otherwise?
Trying to establish your tune being correct. That's 1st on the hierarchy before chasing down the cooling system.

Watch it run with the cap off,
Look for bubbles indicating a breech of compression gasses.
Again with the cap off, When the thermostat opens , there should be substantial flow of water. There should be no doubt in your mind. If you think it maybe kinda opened but not sure it either didn't or the water pump impeller isn't pumping. There could be several reasons for that. Restriction, impeller or impeller rotation.

Just for perspective, I timed my truck for you, on a 70* day my truck has been idling for 53mins 48 seconds for the fan to turn on. I can watch the Tstat open and close on the scanner.

 

You find the numbers-
It will give you the application of that engine. Say a 1991 Chevy van.
Then you look up the belt routing for the application.
That's how that works, the numbers won't say reverse or standard water pump.

You could just take it off and look, end the guessing.

 

It runs well other than this overheating issue. I did have to get the fuel/air mixture tweaked and fiddle with the dizzy to get it smoothed out and pick up well off the line. But now, it runs well, IMO....other opinions may vary.

No bubbles that I saw, and the compression leak tester I used didn't indicate any gases making it into the radiator. I tested it continually until the thermostat popped...which, now that you mention it, I didn't notice it happening even with that syringe tube jammed in the filler neck. BUT, when it pops, it's evident on the gauge, you see it drop back down. Still a mystery.

 

being the location you are ( above freezeing most of the year ) you can run a 10-25% anti freeze to water mix so it lubes the water pump and helps control some corrosion ( I use distilled water not tap as it allows the a/f more life as it doesn't have to fight contaminants and helps raise the BP ) as the EG or PG in antifreeze is not a good transferant of heat and once it absorbs it it doesn't reject it at the radiator as well , water will work better , also do not use water wetter its a acid ( surfacant ) , and unless you use a sacrifical anode it will eat the snot out of the radiator if you have a iron block as it generates electrolysis greater ( makes the cooling system into a battery , on the race cars many of us have had problems with the water wetters eating aluminum heads, water pumps and radiators up) , if you cannot reject heat fast enough a detensioned water is not going to help, its a crutch the only way to reject more heat is air thru the radiator or more surface area in the radiator , and the radiator you have should be more than enough surface /transfer area . another thing is also to back wash the exterior fins ( spray water from engine side out ) to see if any dirt or dust is lodged on the exterior of the fins , on the farm trucks we have it will lower water temps greatly and even the road trucks there is a lot of dirt in them from road grime .

but physically check timing to make sure its not retarded as retarding will heat up a engine more than over advancing it ( a retarded motor will not ping like a over advanced one as a retarded motor throws the heat into the cylinder wall ) make sure the balance hub didn't slip as it will read its on tdc but be retarded on the timing I have oem style balancers slip as much as 20 degrees ) a old or cheap timing chain also can retard the timing too and make it run hot .

as for the water pump you have to pull the back off to see what rotation it is , only aftermarket pumps stamp the numbers on the front , and 305's can be either as they were used in the v belt and serpentine configs . and I have seen/recieved some rebuilt pumps that were assembled or packaged wrong . ( and would cause delayed overheating problems but idle ok )

 

the popping and going back down is normal as its equalizing the pressure built up from the pump against the thermostat and purging the air space in the radiator .

 

Here's a rough sketch of the blade pattern, looking at the water pump from behind with the cover removed. Didn't have my phone at the time.

 

Found a pic, mine looks like the one on the left....

 

The caption for that pic says its original from 1969
http://www.superchevy.com/how-to/148-0504-cooling-system-info/#__federated=1

 

How many rows of tubes is your radiator? If it is only a two row core that could be part of the problem as not enough fluid passes through the core. Here I have seen some people put a faster flow water pump on for this, stupid move as the fluid needs to spend sufficient time in the core to be cooled.

Doc.

 

Specs online say it's 2 1" rows....not entirely sure though.

 

Considering the other factors you have systematically eliminated-For the time it would take (an relatively low expense)to throw a pump on it and a new cap-you would eliminate those items if the problem persists.
BTW-This engine doesn't have Vortec heads on it does it?

 

Does it overheat while cruising at 55+ MPH, yes or no? If not, it needs more pulled through the radiator while standing still.

 

Looks like a reverse rotation impeller to me.

 

A new 75 Chevy water pump is $20! ... How is coolant going to flow if you noticed your lower hose collapsing before?

 

Bingo....fix the bottom hose

 

I live in the NM desert at 6000'. I like to play with big blocks. Let's say I have a lot of experience keeping big v8's cool in the summer in traffic and on cruises.

Here's what I've found worked for me in my coupe. Your mileage may vary. Not traditional but was never intended to be (only inspired) so FWIW. 55gph electric water pump. Moves an ocean at the same high speed, whether you're at idle or rolling at 60mph. 100% water with 1 can water wetter. water pulls heat better than any antifreeze mix. Swap in antifreeze for winter if stored. Aluminum radiator dusted w black paint on the front so as not to stick out like Osama at a bar mitzvah. Spal electric fans with as high a cfm rating as you can get for the diameter you can fit. I run 1 3000cfm puller all the time, 2 x 2000cfm pushers off a toggle switch. All are mounted right against the radiator. Shroud was a FAIL. Tried it every way to Sunday. With trap doors, without, with holes... No go. Thermostat only needed in winter. A 160 so as to get me up to 160 seems to work for me as it should. In the summer, the water temp cruises right on past 160 and the thermostat is just open all the damn time acting as a restrictor in the circuit. Some might say "you don't want the water to move too fast. The rad don't have enough time to pull out the heat." I vehemently disagree. And I've tried it first hand. It's a closed system - water taking its sweet time in the rad is offset by water taking its sweet time in the block doing the opposite. Move it fast as possible and with as little restriction as possible to pull that heat out of it at every possible moment available.

Also, I've found that keeping the initial timing up a touch as well as the idle circuit on the fat side helps reduce the rate of temp climb at idle. Retarded timing and lean carb will build heat fast.

I'm skunked by having to run a '32 Ford sized radiator to cool a 10:1 523ci blown BBF making sizable power. Even with all of this, I typically run about 190 in the summer. It will slowly creep up if I'm stuck at a light to maybe 210 if its bad traffic, then try to fall to 190 once I get rolling again. Again, this has been my personal experience in a "me vs. BBF water temp" fight that lasted 1 full summer of trial and error.



Oh yeah, with the electric water pump and 1 big puller hooked into the ignition circuit, if the temp does happen to get away from me, I can pull over & shut down, turn key to "on" and literally within 3 minutes have the temp down to 190 while the pump circulates and that big fan pulls off the heat. Fire it up and fall right back into line.

 

also on the shroud...you have a narrow radiator. With biggest fan you can fit, fan should be covering a LOT of the radiator.
Collapsing hose is a SURE killer. Some hoses come with a coil spring to help resist that.
Collapsing hose also suggests pump is working strongly, so likely correct rotation!

 

A lot of great advice in this thread! I'm going through it methodically. I replaced the water pump (previous poster reminded me how cheap they are), and I'm glad I did. I finished taking the impeller cover off and the inside looked like a craggy cave! I was able to get a 15" fan that will fit on the front of the pulley and gets as close as 3/4" or so to the back of the radiator. I will relocate the puke tank, but the fan I had on the back is right out....fan comes up too far. I will probably put the fan back on the front, as it was on the top half of the radiator, and then let the mechanical fan pull from the bottom half. I might run it without any electrical fan, first, to see how it does.

NOTE: I also forgot how much I hate replacing water pumps. I drained the block as best as I could after removing the old pump. I used some black RTV to give some "stickum" to the provided gaskets. I like putting a thin coat on both sides. However, when putting the pump back on, all the jostling makes the block seep fluid some more....and getting those lower bolts in can be a big B. If I'd have thought back to the last time I did it, I stuck the gasket to the pump, put the bolts thru, THEN put it on....oh well, next time. Hopefully the leaking water didnt jack with the RTV or gaskets too bad, I reckon I'll find out soon enough!

 

For Next time,
Take the pump off.
Place drain pan under front of engine.
Jack up rear of car.
You'll drain some more.
Let rear down, jack front up a bit to slip 2x4 under tire.
Stay dry as a bone