Hot 350 or not

[pcguy]

Trying to tidy up this 350 Vega for the upcoming drag season and one of the things on my list is to determine if, and if, why it appears to run hot. Started out this morning by checking the timing/vacuum which appears all in at 51 degrees at about 3000RPM. The problem I sense is the temp gauge is not a known quantity to me and the location of the sending unit is questionable – see photo.



I frequently see the gauge reading 210-220 cruising at 65 on a hot day and at the track after a run it can be a little higher. The problem may be related to the sender being between the 1 & 3 exhaust ports. I check the sender with an infrared gun and when the gauge is reading 155 the infrared reads 195 and of course, this is not in itself comforting.

According to the infrared gauge, there is a 60-70 degree difference between the sender on the head and the sender on the back of the intake manifold for the electric fan. BTW, the fan is set to 170 and the thermostat is a 160.

I think I need to do something but I’m not sure if the engine runs hot or not.

How would you proceed?

[T-FATTY]

Buy a new from any auto parts store and place in the intake.

[cjbiagi]

The sender is measuring the temperature of the coolant inside the head, you can't expect to get a accurate reading of the sender by measuring the outside of the sender where no coolant is. The location of the sender should be fine, that's where the stock senders go so I wouldn't worry about that. You mentioned your timing being all in at 51 degrees, is this with the vacuum can disconnected? If so, that is way too much. It should be maxed out at about 38 degrees. If it is with the vacuum connected then that would be about right.

[pcguy]

The sender is measuring the temperature of the coolant inside the head, you can't expect to get a accurate reading of the sender by measuring the outside of the sender where no coolant is. The location of the sender should be fine, that's where the stock senders go so I wouldn't worry about that. You mentioned your timing being all in at 51 degrees, is this with the vacuum can disconnected? If so, that is way too much. It should be maxed out at about 38 degrees. If it is with the vacuum connected then that would be about right.

Here are the readings I just took:

Initial 1000rpm = 14 no vacuum
3000 rpm = 31+ no vacuum
3000 rpm = 54 with vacuum & no load

[pcguy]

The sender is measuring the temperature of the coolant inside the head, you can't expect to get a accurate reading of the sender by measuring the outside of the sender where no coolant is. The location of the sender should be fine, that's where the stock senders go so I wouldn't worry about that. You mentioned your timing being all in at 51 degrees, is this with the vacuum can disconnected? If so, that is way too much. It should be maxed out at about 38 degrees. If it is with the vacuum connected then that would be about right.

Here are the readings I just took:

Initial 1000rpm = 14 no vacuum
3000 rpm = 31+ no vacuum
3000 rpm = 54 with vacuum & no load

[cjbiagi]

Ok, does the mechanical advance (vacuum disconnected) ever go any higher as the rpm increases? Many time you do not see full advance at 3000 rpm's. Since you have a infrared thermometer try reading the temp on the inlet tank on the radiator. That should give you a pretty good indication of the coolant temp entering the radiator. There's quite a bit you can do with the cooling on these cars and every little bit helps. Here's something I wrote a while back on cooling:

There have been tons of tips over the years on cooling. There really should not be any issue with cooling while driving above 30 mph or so. Start with the basics, a good radiator ( I highly recommend an aluminum), proper molded hoses, a good mechanical fan with a shroud, make sure your cooling system is full of no more than a 50% solution of antifreeze along with a bottle or two of Redline WatterWetter, make sure your overflow system is connected and you have a proper radiator cap. Thermostats are always a controversy, I believe in running one since millions of cars use them and they don't overheat. An auxiliary electric fan is always a plus and adding some sheetmetal ducting in between the grille and radiator to direct all of the airflow through the radiator is a good idea. That will vary by make and model, but I added some simple sheets to help direct the air to the radiator and it did help. Also run a good air dam under the front grille area to create a low pressure area under the car as well as behind the radiator which will help promote air flow. That's pretty much the basics, after that you are looking at tuning the engine for the correct A/F ratio and ignition timing which can help. Try running full manifold vacuum and see if that helps your situation since all engines are different. Doing all of this should help with 90% of any cooling issues. Granted the temp may still rise if you are stuck in traffic or God forbid, you are in a parade. There will always be a bit of an issue because of packaging, it's a small engine compartment with a relatively small radiator, but these things should keep you out of danger."

[pcguy]

Maybe I'm on to something – read this page about radiators/cooling http://www.flowkoolerwaterpumps.com/cooling_faq.html and decided to bleed the air out of the cooling system. Along the way I decided to check the surface temperature (160 thermostat) like Clyde suggested above. Probably didn’t get all the air out yet, but the hottest part of the radiator is the lower passenger corner at 155-160 and the coolest at 110 was the driver upper corner.

Does this sound right to you? Could this be the wrong water pump for this 350?

[cjbiagi]

The drivers side upper corner is the inlet to the radiator so it should be the hottest part. The lower passenger side is the return to the engine after it has passed through the radiator and cooled down. Your temps seem reversed for some reason? Of course I am used to a Monza radiator so maybe I am missing something here. However, the side that goes to the water pump is the return from the radiator so it should be cooler than the other side.

[chevyart]

when you point that gun at the bottom passenger side outlet i believe the temp should be around 145 degrees. real lean carb will make that baby run hot. just ask me. also i would want to know what my total advance is(should be as cj said, 36-36 degrees total.) and i would want to know with out vaccum hookup. vaccum advance doesnt belong on a race car. too many things to go wrong. as far as the timing goes, it probably should never be over 36 degrees with flat top pistons and between 37- 40 with dome pistons. art

[283vega]

Could you be running a reverse direction wp the wrong way? Or another way to say it the the wrong pump for the pulley set up you have.

[pcguy]

At the time I took these readings, the temp gauge on the dash read 165, so at that moment, the engine was not running hot. Pulled the cap with the engine off, started it up to see if I could tell which way the coolant was flowing, but the only thing that happened was coolant bursting through the cap opening.

With the engine cold, I’ll pull the WP belt and spin the fan manually to see if there is any movement. Spinning the fan clockwise in this manner should produce zero movement, especially toward the engine.

The pulley setup us a standard v-belt on an old vette iron block and heads - fan is running clockwise. Bought this vega with this setup so it's not known to me.

Also, talked to the counter guys at the local Napa Auto and the didn’t know of a pump for an older 350 that works CCW They thought the pump impeller may have come loose from the shaft.

One other thought, there is definitey still some air in the system and at the time this happened, the heater core was out of the firewall and hoses were plugged.

[Monza Harry]

Hi PC I believe that twin V8 Marine app's engine would have 1 forward & 1 reverse water pump as that is pretty standard arrangement in larger boats (each engine rotates oppisite to each other, pre serpentine belt era). I am sure Spencer will weigh in as a good part of his business is marine and he is very knowlegeable on these things. It is possible someone installed one unknowingly in the past, seems you are on the right path to solve your issues, Good Luck with your Ride Harry

[cjbiagi]

You never want to remove a radiator cap from a hot engine. Wait for it to cool and then remove the cap and start the car, once it warms up a bit you should be able to see the coolant flow and see which way it is going.

[pcguy]

No luck with manually turning the fan – inconclusive.

Need to get a good hose clamp for the heater core and fire it up to see if running cold it will show coolant moving at the cap. Still need to properly burp the air out of it.

Did consider a blown head gasket, but there is a 10lb. cap on it and it never leaks or overflows.

[cjbiagi]

I always run the engine with the cap removed to allow the air to escape after working on the cooling system. So, doing that will help accomplish that as well as seeing the coolant flow through the core. Eventually it may start bubbling over so keep an eye for that. When that happens it's time to put the cap on.