Howdy! ...I recently seized the motor on my 67 Mustang. It was a 289. I found a 1971 302 engine, I believe it was originally in a Bronco. I put it in, it seems to run fine But overheats mediately.(within five minutes)
I have the heater core bypassed, put in a new thermostat that I tested on the stove first, I put in a new water pump. Top and bottom radiator hose both seem equally hot. I put in a new temperature sensor. Everything seems to be circulating, I’m kind of running out of ideas. It overheats when you’re driving it too ...so I’ve got good airflow. I’m wondering if maybe the 289 radiator was too small.( It always did run warm to begin with)
I tried bleeding all the air out of the system by filling the radiator while it was jacked up so the highest point was the top of the radiator. I just don’t know… Any thoughts? Oh, by the way it has an older cast iron Edelbrock intake manifold and a four barrel Edelbrock carburetor. Any thoughts or suggestions as greatly appreciated! Thanks!

 

Got bubbles in the coolant? Head gasket issues will push combustion gases into the coolant causing an overheat. Just a theory....

 

No bubbles at all, coolant has stayed nice and clear has has the engine oil...I was thinking perhaps the previous owner had the head gaskets on wrong... I can see a tab of the head gasket sticking out on the lower front bottom of each head, I’ve heard that that’s an indication that they’re on properly.
A friend suggested that I might have a reverse rotation pump on, and I got it from AutoZone, it’s a Duralast and in the specifications it doesn’t say anything about rotation. It says standard duty… But when I took the backing plate off of it before I put it on, it had kind of a fan blade type propeller instead of an enclosed, round disk propeller system like my old one.

 

The radiators in the classic Mustangs don't work very well by their design. The top-down arrangement where both inlet and outlet were on the same side tended to cause most of the coolant to flow only through part of the radiator. Even so, the early Mustangs did not overheat in the first few minutes of operation as you described.

This doesn't seem right to me. If the radiator is doing its job, the bottom hose should be much cooler than the top hose. So I wonder if you have some tubes in the radiator built up with corrosion? They may allow fluid flow, but insulate them from the surfaces of the tubes. You might have it checked out at your local radiator shop. If your core is in good shape, they can "rod" it out; basically a thorough cleaning of the core. I had that done to one of my cars and the cooling system worked much better afterward.

 

I'd follow that up.

 

Thanks for your input! Sounds like a good idea. When I had the radiator off I flushed through it top to bottom and also the reverse...water seemed to flow out good enough, but like you said, having the inlet and outlet on the same side gives some leeway for a large part to be missed. I will call around and see if I can find a good radiator shop to check it out. Even with the original engine it always ran alittle hot.

 

Oh, by the way when it is overheated all the hoses are hot And feel tight like under pressure ...top and bottom radiator hose, heater bypass hose too.

 

I thought maybe I had an air pocket that was blocking it, I wasn’t sure of the best way to clear that out… So after I changed the water pump I jacked the front of the car up so the top of the radiator was higher above everything else and filled it with the engine running and the cap off.
By overheating I mean if I run it for five minutes, it pegs out hot all the way on the gauge. My gauges on the 67mustang were kind of iffy before so I just put in a brand new constant voltage regulator for the gauges in the dash and a new temperature sending unit in the manifold.

 

Did you check the rotation? That seems very likely at this point.

 

I’m not sure if there’s a way of checking the rotation without removing the water pump… Maybe taking the inlet hose into the manifold loose and starting it to see if it shoots out antifreeze into a catch reservoir? Otherwise it’s a real pain taking back off the water pump to look at the impeller. And the weird thing is, it was overheating exactly the same before I change the water pump.

 

I'm sorry, but I beg to differ on this...... been driving and racing these guys since the 70's...what is recognized is the absence of of understanding the different types of radiators, materials and thermal heat transfer.

 

Assuming everything else that has been stated is ok, the early 70's bronco 302's were very sensitive to ignition timing.... any more than 2 degrees initial advanced of the distributor set to the more aggressive advance position from oem and they would run hot..... the 2 core radiator is more than adequate for any SBF assuming there is no AC, etc. Another real potential is the lower radiator hose....it could be collapsing on you causing a flow restriction... the originals had a spring inside to keep this from occurring. Also, if you are using a "lever-vent" type radiator cap, replace it with one that does not have the level....these have been known to provide less psi that rated and it will contribute to the engine running hot. Also the coolant mix...... 50/50 concentrate of ethylene glycol type only!!!! A concentration of much greater than 50/50 can in normal or hot climates induce the engine to run hot. I would also do a flow test on the radiator.... it could be very well not circulating the coolant fast enough or your cooling jackets in the heads may be partially blocked or it may also be flowing too fast...

One of the things that did change was the "high flow water pumps" which came about in the 80's+ which reduce the time the cooling system has to absorb heat and dissipate heat......... and believe me when I say this.... I know of very few people who didn't have an issue of their cars/trucks running warmer when these were installed as replacement units! if by chance you have an original untouched radiator that is still performing correctly, this may be the issue and if the flow is slowed back to OEM spec's, (which can be accomplished with flow restrictor installed in the upper radiator hose) you will see (typically) temp reduction- and the ability to maintain operational temp range greatly increased.

But, IMHO, my gut instinct is telling me you have a flow issue...either radiator or cylinder head based.... and IMHO, I do not use any chinese made radiators in any of my vehicles.

 

A lot of information there! Thanks I appreciate the time you took thinking all that through! At this point I am thinking it either has to be the radiator, it’s 53 years old and has never had any work done to it… Or like you were saying blocked cooling jackets in the heads. I’ll double check the timing and try to get it more exact. The lower radiator hose doesn’t have a spring in, it when it has overheated both the top and Bottom radiator hose seem real solid, even when you rev it up I don’t see it collapsing. I do have a lever vent on my cap, I’ll get rid of that and go to the standard. I have been using the pre-mixed 50-50 radiator fluid. I’m going to call a few radiator shops and get some prices on them working on the original one, I have been looking at a few of the aftermarket radiators, but like you said I’m always leery of the parts. Almost everything is made in China now.

 

Yup- 53 YO radator is likely the issue but IMHO, you're on the right track as far as finding a shop to boil it out, recore it, etc.!!!!

Just in case that doesn't work out and you need to buy a replacement, I highly recommend US Radiator and they have been around for 40+ years. The guy who presently owns it started working there 30 years ago and with the exception of 1 or 2 items, everything is built at their facility. They are also great to talk with on the phone and if you tell them exactly what you have, what are your concerns or wants, they will tell you exactly what to order. I don’t know of anyone (including the racing community) who has not been pleased with them!

Link: U.S. Radiator | The Difference Is In The Tooling

US Radiator Corporation
4423 District Boulevard
Vernon, California
323-826-0965

Another option that is less expensive...

I have always purchased from US Radiator, but when the radiator plastic part began failing on my wifes 97 Cougar Sport (which lasted 17 years with an anode), called them and it's too new of a car and they recommended:

Radiator Express
www.radiatorexpress.com
Irvine, CA
866-723-3977

I was very pleased with the product, it was built exactly to the oem specs. What I liked about this place is when I spoke to their support staff, the person I spoke with had definitely experienced getting their hands dirty on a car.......when I asked questions, I got answers....no hesitation. Whit I also liked is they track installation issues that both mechanics & customers have so when you place your order, they order the brand/mfg that has the least amount of reported issues.

 

Keeping your cooling system in good shape helps make them work better under all conditions.

As to radiator design, there is a reason that all new radiators are cross-flow, instead of the old top-down designs. On the top-down design, the radiator cap is on the hot side, so it WILL release pressure well before its rating. It is also susceptible to water pump pulses that can overpower the cap's spring pressure. I currently use a 22 psi cap, instead of the stock 16 psi spec, on my 1969 Mustang, and I've had less incidents of excessive overflow. All new cross-flow radiators put the cap on the cold side. Even so, I find that if I run without a shroud, the engine will get hot in stop-and-go traffic on a hot summer afternoon.

Other than that, the top-down radiators that have both their inlet and outlet on the same side have been shown to not fully distribute the hot coolant to the entire core. This is due to natural flow behavior; the coolant will take the path of least resistance. So their effective cooling capacity is less than what they're capable of.

About the spring in the lower hose, that's installed at the factory to facilitate evacuation and fill; they apply a vacuum to the system when filling to eliminate trapped air. The spring prevents the hose from collapsing during that process. If your lower hose is collapsing at high rpm, there is a flow restriction that's causing it. Remember that the system should be operating at 16-20 psi, in addition to whatever the pump is putting out, so none of the hoses should be collapsing.

As far as flow rate, you want the coolant to flow through the hot parts as fast as possible, so it can pick up as much heat as possible, since heat flow is directly related to temperature difference between the hot part and the cooler coolant. The faster you can get cooler coolant through, the faster the heat transfer Then in the radiator, you want it to flow as slow as possible, to transfer as much heat to the air as possible. So the best arrangement is to have a radiator with as much volume and exposed area as possible. The larger the volume, the slower the coolant flows through it. Just maintain a lot of air flow with the fan.