New build overheating

[jstek]

Hello there. Hoping for some guidance. I have a 1969 Bronco that was just completely renovated. The 302 engine is a rebuild and literally ever other component is new. It runs just fine with city driving, staying at around 180 degrees. However, if I let it idle or drive at slow speeds for more than 15-20 minutes it starts to overheat (upwards of 240 degrees and then I turn it off and let it cool down). The first time I drove it slow on dirt roads I didn't notice until it hit 246 degrees and the coolant was literally boiling in the reservoir. Scary. The coolant is a mix of mostly antifreeze, some water, and some Radiator Relief. The electric fan is a Derail 17" high output fan. The thermostat is a Robert Shaw 180. I have confirmed that the fan is coming on at 180 (actually a little lower). It is overheating without the A/C on and an ambient temp of only 55-60 degrees. This is a real problem because I mainly want to drive this thing on the rutted dirt roads near my house that require 2nd gear and no more than 15-20 mph. Any thoughts on what could be wrong? Many thanks for any thoughts.
(PS I would post photos but not sure how to do it on this forum??? Sorry, newbie)

 

[doran4x]

Derale 17” high output only pulls 2400 cfm. Not enough flow.

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[Wild horse 75]

Have you confirmed the fan is blowing in the right direction? Not trying to be a dick but I’ve seen it more than a few times. People assume and just listen to it come on but don’t check to make sure it’s going the right direction. Also I like to have the fan come on 5-10° cooler than the thermostat is set at. Have you ensured you don’t have any trapped air? Air reads hotter than coolant. Also you should never have more than a 50/50 antifreeze to water mix. Antifreeze actually isn’t very good at heat transfer since it’s so slippery. Heat transfer relies on water sticking to components to draw the heat out. I would also invest in an infrared heat gun so you can check and see if maybe you’ve got a bad gauge or sender.

 

[Timmy390]

Derale 17” high output only pulls 2400 cfm. Not enough flow.

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Maybe...but I run that same fan on my 351w with 195 stat and it stays cool even on the hottest Arkansas summer day. Runs 210 most of the time. Does drop to 200 when on the highway. Creaps to 220 when in stop and go traffic on the hot days. I run a mechanical gauge.

Tim

 

[Brush Hog]

Was cooling system purged? Miaybe air trapped in system.

 

[ba123]

And what do you mean it's boiling in the reservoir? Maybe your cap isn't holding the right pressure...not positive but air coming in would lower the boiling point.

And yes, like other said, the air will read hotter and not give an accurate reading.

Also, straight coolant won't cool as well as the proper mix will. Just get the premixed stuff and you're good.

Antifreeze raises your boiling point and lowers your freezing point but water transfers heat better.

 

[nvrstuk]

Radiator condition?

Wtrpump condition?

That fan is marginal.

How new is the engine? New engines have a lot more friction happening than after break-in.

302's cool super easy unless one of the components isn't working properly. Were these parts working perfectly and were these parts on the old engine. We need to know what isn't working, what worked before, and without that info we are only guessing.

 

[73azbronco]

what viscosity? 30w is a well known break in oil, lower than you may want long term, but transfers heat much better than thick oil.

agree with above, verify it is purged, easiest way I know, jack front end up, way up, start engine verify full, pull heat verify heater purged.

You said coolant and some water. best is 50/50, higher coolant percentage does not cool better, in fact transfers heat slower, water being best way to transfer heat. But, obviously, water at 230 will blow the cap off. ok i repeated stuff, sorry

agree your fan may not be the best.

Shroud? probably one of the top three why it wont cool, water pump, shroud, radiator, fan. Ok, top 4.

 

[nvrstuk]

He's gotta send pics and give more info...

 

[doran4x]

I’ve had bad radiator caps out of the box. Get a pressure tester and make sure it holds.


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[nvrstuk]

Hello there. Hoping for some guidance. I have a 1969 Bronco that was just completely renovated. The 302 engine is a rebuild and literally ever other component is new. It runs just fine with city driving, staying at around 180 degrees. However, if I let it idle or drive at slow speeds for more than 15-20 minutes it starts to overheat (upwards of 240 degrees and then I turn it off and let it cool down). The first time I drove it slow on dirt roads I didn't notice until it hit 246 degrees and the coolant was literally boiling in the reservoir. Scary. The coolant is a mix of mostly antifreeze, some water, and some Radiator Relief. The electric fan is a Derail 17" high output fan. The thermostat is a Robert Shaw 180. I have confirmed that the fan is coming on at 180 (actually a little lower). It is overheating without the A/C on and an ambient temp of only 55-60 degrees. This is a real problem because I mainly want to drive this thing on the rutted dirt roads near my house that require 2nd gear and no more than 15-20 mph. Any thoughts on what could be wrong? Many thanks for any thoughts.
(PS I would post photos but not sure how to do it on this forum??? Sorry, newbie)

pics.

I was going to post the page that shows how you sign up to be a member but after 10 MINUTES and NO LUCK I gave up. Somebody will find the link hidden somewhere (probably on the frt page) but I sure can't find it.

 

[Soylent]

https://classicbroncos.com/forums/threads/how-to-upload-photos-become-a-contributor.34373/

 

[B RON CO]

Hi, another thing to check is ignition timing. If the timing is retarded, or for some reason the timing does not advance, you will run hot. Good luck

 

[frdboy]

All good info above, another thought is what water pump and is it spinning in the correct direction.

 

[Johnnyb]

Couple of thoughts here:

Verify your temp sender and gauge. I recently had a situation where due to misconfiguration of the temperature sender, I was shutting down due to perceived overheating when in fact it was running perfectly. Also when your temp gets to 240 or above there are visible and audible signs such as boiling in the block and pissing antifreeze out on the ground, if that didn't happen you probably weren't overheated.

I always drill a small hole at the top of my thermostat inside the water passage but outside the thermostat mechanism so as not to mess it up. The point of this is to allow any air that might accumulate at the top of the block to bleed through. If there was a pocket of air below the thermostat it might never open up and you might get overheating especially in a motor that was freshly filled. This might also be accomplished by simply opening the heater depending on your configuration.

Lastly I advocate strongly for the Explorer front dress on the motor. It looks great and works great and leaves more room for a larger radiator such as the Ron Davis that WH sells, in the event cooling issues cannot be alleviated in any other way. Explorer front dress can be had inexpensively from one of the members here on the parts for sale page.

Hope this helps!
-JB

 

[jstek]

Thanks for the input. Few things: the fan is installed correctly (paper sticks to grill when on) and comes on at about 165-170. The water pump and radiator are new. The engine has about 250 miles on it. Any suggestions for a different fan? Also, when I say overheating, the engine is not stopping. The temp gauge just gets super high and I shuck the engine down for fear of damage. I do believe it is actually hot, though.
(And for background...this was my late husband's Bronco. He had it stock as a daily driver for a long time. He had just started this renovation project (bought a garage full of parts and stripped down the old Bronco completely) when he unexpectedly died. So this has been a long project for me to try and see through, and I am not really a car person. Several mechanics have been scratching their heads on this overheating issue, so I'm trying to gather ideas from this forum to help hunt down the culprit. I will have them check on the ideas presented thus far.)

 

[ba123]

Sorry to hear that...he was a lucky man and I'm sure he knew it! That is awesome that you finished it for him!

Wow.

Hope you get it figured out.

 

[Broncobowsher]

Need a picture of the other side of the radiator. Fan, belts, etc.

Low speed (idle) cooling issues are generally airflow issues. I'm 95% sure the fan isn't up to the task. For one I don't see a shroud, so the fan only moves air directly under the blades and the rest of the radiator isn't being cooled. Worse is hot air from under the hood is going forward through the radiator and doing a U-turn and getting sucked through. So even less cooling. Add in CFM ratings on aftermarket electric fans are just about meaningless. Fine if you want to use it as a window fan in the shop. But put a load on them and the airflow drops. Very few fans will actually publish airflow ratings at pressure drop (Spal generally does).

I see an aftermarket A/C compressor. That is even more fan load. Even with the A/C off, just having the condensor in front of hte radiator is more airflow restriction.

In general, the only cooling fans that work are those from OEM applications. I forget the list of what works. Turaus, PT Cruiser, others. I want to say there may be two aftermarket electric fans that are known to work. And all the fans that work take a LOT of power. Figure a 40 amp load.

Driving at speed, don't really need a fan. Ram air will push through and keep things happy. That generally proves the cooling system is good. You are also working the engine harder, making more heat as well. So staying cool going down the road is a good cooling system. I'm still calling it an airflow issue. Pretty sure it is a wrong spec fan for the application. But want pictures to back my thoughts.

 

[gnpenning]

That's a nice looking bronco.

Lots of non stock parts which is fine but the reason for my question. The coolant temp sensor needs to be in coolant and the right location for it to read accurately. Have you verified the sender location? You may have the sender in a location that isn't properly reading the coolant temp.

A cheap harbour freight IR temp gun ($20?) will give you an idea about temps in different locations. Simple to use, pull the trigger and point the red dot at different locations and and get the readings. Check thermostat housing, upper and lower radiator, etc. Much cheaper than paying a ship and we can help you out with questions.

Like mentioned more pictures of the engine side of the radiator. The more the better. Don't worry about it, we like pictures and you should have noticed plenty of people here willing to help.

 

[nvrstuk]

https://classicbroncos.com/forums/threads/how-to-upload-photos-become-a-contributor.34373/

Thanks! lol