Boiling over.......

[Sand85]

Hi, my problem is the my 85 Chevy c10, 305 with th350 automatic transmission is over heating and boiling over into the overflow tank. I have changed the water pump and have flushed the radiators twice and even parked the truck on blocks because of air bubbles that I read somewhere. Funny it overheats at idle and not while running. Any suggestions would be helpful, thanks

[Matt Man]

Are you running a fan clutch? If you do have one is it in good shape? Would be a good time to upgrade to a 5 or 7 blade fan with a new fan clutch.

[tucsonjwt]

x2 on fan clutch. See if the clutch is turning the fan when the engine is hot and at idle. You could also have a bad water pump - look under the truck to see if you have a trail of rusty water from the weep hole at the bottom of the water pump. That rusty trail indicates a failed water pump.

I would only use a AC Delco fan clutch if you need one - about $100 at the oem vendors, the last time I checked:

www.oewarehouse.com
www.oehq.com
www.davesauto.com
www.gmpartsdirect.com
www.rockauto.com

Get the GM part number for the clutch and search Amazon and Ebay also.

[D13]

Do you have a thermostat? If not you may be moving water thru the engine too fast for it to cool.
I like to run a 190 thermostat with a small bypass hole drilled in it, which will let those air bubbles move to the radiator, and allow hot water to flow past the thermostat quicker during warm up (decreases the sudden spike right before the thermostat opens).

[Sand85]

Originally Posted by Matt Man

Are you running a fan clutch? If you do have one is it in good shape? Would be a good time to upgrade to a 5 or 7 blade fan with a new fan clutch.

The truck didn't come with one and so I was under the assumption that it didn't need one, plus it has this aluminum shaft that bolts on to the belt pulley.

[Sand85]

Originally Posted by D13

Do you have a thermostat? If not you may be moving water thru the engine too fast for it to cool.
I like to run a 190 thermostat with a small bypass hole drilled in it, which will let those air bubbles move to the radiator, and allow hot water to flow past the thermostat quicker during warm up (decreases the sudden spike right before the thermostat opens).

Unfortunately, I wasn't running a thermostat when the temperature spiked and still currently it sits without a thermostat. I did go the AutoZone and pick one up but I don't remember the rating. I even changed the thermostat housing.

[ultrahd4me]

I agree with the others. Get a heavy duty fan clutch and the correct fan shroud and you will be running cool.

[Sand85]

Originally Posted by tucsonjwt

x2 on fan clutch. See if the clutch is turning the fan when the engine is hot and at idle. You could also have a bad water pump - look under the truck to see if you have a trail of rusty water from the weep hole at the bottom of the water pump. That rusty trail indicates a failed water pump.

I would only use a AC Delco fan clutch if you need one - about $100 at the oem vendors, the last time I checked:

www.oewarehouse.com
www.oehq.com
www.davesauto.com
www.gmpartsdirect.com
www.rockauto.com

Get the GM part number for the clutch and search Amazon and Ebay also.

I happen to change the water pump and the alternator at the same time because it had a dead battery but that's a different issue. I figured I was there already why not, lol!


Thank you for the links I will be and have looked at some of them.

[hatzie]

You're missing the fan shroud and the stock clutch fan.
https://www.google.com/search?q=1985...hroud&ie=UTF-8
Engines can overheat just sitting without the shroud to direct airflow through the radiator. A properly working fan clutch will improve fuel mileage and improve cooling at idle.
Install the thermostat as well. It'll keep the heads at a more consistent temperature.
Install a new radiator cap as well. This will keep the system pressure at 12-15psi. Pressure raises the boiling point.

The missing thermostat and fan clutch says there was a problem before they were removed. It might be as simple as the bad water pump or it may be more

[Dead Parrot]

Most SBCs specified a 195 thermostat. Haven't tested it myself but several folks claim that running no thermostat degrades cooling because the coolant moves too fast through the radiator. Maybe too much speed causes turbulence that limits heat transfer.

If that is a flex fan, add a stock 7 blade fan to your list.

Might research doing a switch to electric fans. May be cheaper then obtaining the proper parts to restore the OEM cooling setup.

[Sand85]

Originally Posted by hatzie

You're missing the fan shroud and the stock clutch fan.
https://www.google.com/search?q=1985...hroud&ie=UTF-8
Engines can overheat just sitting without the shroud to direct airflow through the radiator. A properly working fan clutch will improve fuel mileage and improve cooling at idle.
Install the thermostat as well. It'll keep the heads at a more consistent temperature.
Install a new radiator cap as well. This will keep the system pressure at 12-15psi. Pressure raises the boiling point.

The missing thermostat and fan clutch says there was a problem before they were removed. It might be as simple as the bad water pump or it may be more

The fan shroud I do have but the fan clutch I will go get. The thermostat will get installed this weekend being that we have a much time to play with our big boys toys, lol! I am hoping that these items help fix this because I had conversations with friends and some said it could be the heads, I'm hoping that's not it.

[Sand85]

Originally Posted by Dead Parrot

Most SBCs specified a 195 thermostat. Haven't tested it myself but several folks claim that running no thermostat degrades cooling because the coolant moves too fast through the radiator. Maybe too much speed causes turbulence that limits heat transfer.

If that is a flex fan, add a stock 7 blade fan to your list.

Might research doing a switch to electric fans. May be cheaper then obtaining the proper parts to restore the OEM cooling setup.

My current fan has six blades and I don't see how one more blade would make a difference?

I have run a 93' Chevy 5.7 with no thermostat and it run fine but I put one in anyways because I was a lot more comfortable knowing it was there.

[geezer#99]

THat six blade fan will work fine.
Put your shroud on it and make sure the blades are Set in the shroud right.
Half in/half out.
You might need a different length scpacer to do that.

[Sand85]

The spacer I currently have is all aluminum, I might be able to cut that to size?

[geezer#99]

Originally Posted by Sand85

The spacer I currently have is all aluminum, I might be able to cut that to size?

Easier just to buy one the right length with new bolts.
IIRC the bolts are 1/4" fine thread.

[Sand85]

Originally Posted by geezer#99

Easier just to buy one the right length with new bolts.
IIRC the bolts are 1/4" fine thread.

What are IIRC's? sorry

[raceman6135]

Originally Posted by Sand85

What are IIRC's? sorry

If I Recall Correctly.

[raceman6135]

Originally Posted by Sand85

The spacer I currently have is all aluminum, I might be able to cut that to size?

Fan spacers have a "knob" on one side and a receiver "hole" in them to register them to both the water pump and fan. Here you can see the "knob" on this spacer. If you simply cut the spacer to make it shorter, you'd be removing this and asking the bolts to keep the fan and spacer perfectly aligned, which they will not as they were never intended to do that.

[hatzie]

Originally Posted by geezer#99

Easier just to buy one the right length with new bolts.
IIRC the bolts are 1/4" fine thread.

Or the correct fan clutch.

[Sand85]

The year is 1985 chevy, 305 V8 with a TH350 transmission. I plan to work on the truck tomorrow.

[Matt Man]

I would highly recommend a 5 or 7 blade fan with a good quality fan clutch, and the proper shroud, along with a 180-195 thermostat. You're in Houston it gets pretty hot there, a fan clutch as mentioned will also net you more MPG.

[Dead Parrot]

Originally Posted by Sand85

My current fan has six blades and I don't see how one more blade would make a difference?

I have run a 93' Chevy 5.7 with no thermostat and it run fine but I put one in anyways because I was a lot more comfortable knowing it was there.

If yours is a flex fan(hard to tell for sure from the pics), it probably has less pitch since the assumption is that it will be running at a higher speed most of the time. When it is running at high speed, it pulls enough air to keep things cool. At idle, not so much. Which is where you said your problem is.

The factory fan has more pitch since GM expected it to be mated to a clutch which allows some slippage. But at slow speeds, it moves more air across the radiator. The one extra blade isn't the advantage, the greater pitch is. If you wind up getting an OEM type fan, they usually come in 5 and 7 blade versions. Might as well get the 7 blade if you make the swap. Some flex fans won't mate to a clutch, depends on the fan.

Adding the shroud may fix the problem with no other changes needed.

[Sand85]

Gentleman, I haven't had time to work on the truck as I had promised. I do another question on weather a fan and clutch from a 79 GMC will work? I noticed that the donor has bolts coming from the water pump pulley and not going in like mine.

This is what I found yesterday in the scrap yard, would it work for mine?

[Dead Parrot]

Assuming the clutch is good, should work. You will need to pickup four water pump studs, nuts and lock washers if you didn't keep the four from yard donor vehicle. That looks like the same type of 7 blade fan mine has.

[Bluestep]

Although I would recommend running a fan clutch, this is not your problem. It will not make the fan turn any faster than the spacer does! The fan and clutch from the wrecking yard should work okay, if the clutch is working properly.
Running without a fan shroud will definitely move very little air at an idle.
Make sure that the coolant recovery system is all working properly so that you end up with no air in the system that can cause an airlock. Also make sure that your belts are properly tensioned.