Good evening fellow forum members. My 79 is overheating at idle. Temp climbs from the 100 degree marking to the "orange" zone within 2-5 minutes of the engine running. After shutting the engine off I put my hand around both hoses and they were firm. I replaced the thermostat with a 195 degree (as I have always used) After replacing the thermostat (195 degree) I started the vehicle and it overheated once again. The backstory is the I replaced the leaking (copper/brass) radiator with radiator with a copper/brass radiator from summit. This has me scratching my head. I installed this radiator two weeks ago.

 

Take off the heater hose from the fitting on the intake manifold. Use a funnel to top up the coolant in the engine. Re attach, try again-bet your block has hardly any coolant in it from when you drained the rad to replace it, presuming this problem started immediately after you changed the rad, which is not entirely clear from your post. My two cents

 

or you changed radiator for overheating and it did not fix the problem. in which case all the seals around and under the radiator are allowing air to go around instead of through the radiator. if this is the case, I may be interested in your old radiator. I stashed my 75 at a friends house. he has some lowlifes come around, somebody got 5 bucks for scrap copper for my radiator... you still have the box summit rad came in?

 

Not to offend, but were the fundamentals checked? Are you sure there is not an air pocket in the system?

 

Is your fan's clutch driving your fan fast enough? Maybe it's freewheeling and due for replacement.

 

It's not overheating going down the road then?

Just at idle, I would agree with nevertooold it's a fan/airflow problem.

 

remove your thermostat, button it up, refill, and let us know what it does.

 

It could as simple as the new thermostat was defective and not opening as the engine comes up to temperature. Could be the thermostat was installed upside down, simple mistake. Did you replace the lower radiator hose? If so make sure it has the spring inside. Some replacement lower hoses don't have the spring and the hose will collapse causing overheating. And as stated above, you may have an air pocket in the system which will also cause overheating.

 

How do you test the fan clutch? Collapsed lower hose could be. The old hose I installed years (14) ago (advaced auto) came with no spring and did not collapse. Thermostat installed properly. Air pocket possible.

 

Lets look at this logically. You replaced the radiator because it was leaking. Was it overheating before you replaced the rad? If not, then the problem is either the new rad, or something you changed when you replaced it. As I see it that leaves you with four possibilities:

1) The new rad is defective

2) You have air in the system that is preventing the water pump from circulating the coolant. (Bleed the system as others here have suggested.)

3) There is a problem with something else you replaced, or reassembled incorrectly. (What else did you change or have apart?)

4) The overheating is unrelated and a complete coincidence. (Pretty unlikely.)

I would attempt to eliminate #2 and #3 as possibilities. If they check out, I think I would probably reinstall the original rad to see if the problem is still present. If it goes away with the old rad, I think the conclusion is obvious. There is a problem with the new rad. Something else you may want to consider is getting the car up to speed on the highway to see if it is still overheating. If not, this tells you the problem is likely related to airflow through the rad. This is a little risky, and I'm not sure I would be comfortable trying it with my car.

Good luck and let us know how it goes.

 

Drwet, Old radiator was leaking/overheating due to loss if coolant.

1. Hope not
2. Will try
3. Only radiator hoses are new.
4. Who knows? Stranger things have happend between this car and I.

Cannot drive it as it overheats at idle.

 

Welcome to the club!

 

Perhaps the assumption that it was overheating due to loss of coolant was incorrect. Is it possible that the overheating and the loss of coolant were unrelated?

 

Old School Rules:

Overheating at idle is a Air Circulation Issue
Overheating at speed is a Water Circulation Issue

You've got to have that spring in the lower hose. You would never see it collaspe because that would only happen after several minutes of sustained speed. But that's not your issue. Thermo or fan clutch more likely.
It never made sense to me to remove a thermostat just to run a test. If you are going to the trouble of draining coolant, remove hose, scrapping the gasket, RTV the thermo housing, refill, etc. Why not just put a new thermo in and be done with it?

 

There's 20 different reasons...

hoses get clogged up,
hose anti-collapse springs get weak, or missing,
your gauge may be wrong, your sending unit may be wrong.
as things age, things clog up, such as passages within your engine,
your timing is wrong,
your carb is too lean
your thermostat may be bad,
your fan may not pass enough air at idle,
you dont have air flow proper sealing around your radiator,
your water level is too low,
your radiator is under capacity.

if I put a 195 in my big block, it would melt... well.. not really, but one time I did, and it spit and sprayed coolant out the cap every time I shut the car off.. hot spots in the engine and it was running way too hot, both idling and on the highway..
I put a 160 thermostat in the car and it has been fine for years.

folks here will tell you that 195 is OK and is what the factory had.. but that is for a new, well buttoned up system, well sealed, proper timed, proper carb setting, no clogged passages, etc.. which a 40 year old car is not...

remove your thermostat, or at least swap it for a 160, and see what happens.

 

Lower hoses can't collapse when they're under pressure. They can only collapse when the engine is cold and revved high.

 

If it’s over heating within 2-5 mins of a cold start, you are not getting water circulation.

 

Again, false information. The bottom rad hose callapes due to a suction created by the waterpump. A spring inside the hose supports the rubber. And they are more likely to collapse when the rubber is hot, not cold.

 

there are weatherstrip-type seals around the radiator. are they in place? fan shroud? pic? I would also think you could start it cold. drive 1 minute away. turn around come back. you should get an idea if temp is climbing faster, slower or same speed as when sitting in driveway.

 

Remove the radiator cap, start the engine and let it warm up. Watch the radiator water level and add fluid to appropriate mark when water level drops. I would bet that when the thermostat opens, the water level will drop a bunch. Once the engine is up to temp and the T-stat is flowing hot water with radiator full, put the cap on and go for a test drive.