Brand new 340 motor running way too hot!

[UKPlymouth]

Hi guys, took my freshly built 340 Roadrunner out for a maiden voyage.
Didn't get too long before the aftermarket temp guage showed as high as it could get. I have some related question;
Is my radiator too small? It's a single core measuring 18" x22" which seems small to me. It also was filthy inside.

Second question. My car has an aftermarket temp guage but wired to the original mopar sender unit. Should I trust it?
All advice appreciated.

All the hoses have got hot water and the rad has no cold spots so I assume thermostat is opening ok.

 

[67Satty]

I think you answered your own question as to why it's running too hot with a couple of the things you said. Single-core? I've never heard of anyone using a single-core. My stock 318 AC car came with a 26" three-core from the factory. You also said it was filthy so that's a problem too.

Besides trying a three-core and/or a wider radiator, you could try things like more initial timing and running a mix of distilled water and Water-wetter. It's normal for new motors to run hotter for awhile but you don't want to start off with strikes against you like a too small or clogged radiator or retarded timing.

 

[Jasoncoronet]

Change the sending unit also your radiator would not cool a Honda I think.

 

[67 coronet]

3 core minimum for the rad.22 inch should be ok.change to a mechanical temp guage.much more accurate and well worth the money to save your motor from misshaps.

 

[UKPlymouth]

Thanks guys, I was told by the vendor the rad was 'original size', but research tells me otherwise. I'm now looking at an aluminium replacement and I will take the advice on a proper temp guage set up.
Car ran lovely, but I need to nip this in the bud!

 

[Bruzilla]

I installed a set of Stewart-Warner gauges into one of my Crown Vics one time and found out that not all sender units are the same. The new gauge read about 40 degrees hotter than the old one until I changed out the sender.

Are you getting any secondary issues of an overheat condition, like steam coming from the vent cap? Sounds like stones rattling in a can when you accelerate (pre-ignition ping)? The ability to smell coolant?

 

[UKPlymouth]

Hi Bruzilla,
Secondary issues. Well sort of, but my fault. Instaled a new brake boster and tok the car down the road. Clearly had the push rod to fa and caused the brakes to strat to seize, the engine got hot and I stoped after less than a mile. The overflow pipe did burp out some fluid. I then re set the brakes correctly, topped up coolant and drove down the road. The engine soon got hot (according to temp guage) and I drove home. This time no fluid was expelled despite the temp guage indicating too hot.
Two things I found out-
1- The rad is full of crap and even after running for a few moments there is a goey mes of brown crap inside the filler cap, so rad needs replacing.
2- I pulled the coolant temp sender from the inlet (cold engine) and was happy to see very clear coolant emege form the hole (newly bult motor). I then swapped in a new temp semsor from my Dodge pick up and started the motor. First thing I noticed is that with ign at run, the temp guage needle moved about a quarter across the dial! So I cant trust the temp guage/sender compatibility.
Finally, now torn between two choices. Have my old singlke core 22" rad recored with three rows by local outfit (expensive)
Or, buy a 22" Champion aluminium rad and have it shipped from the states which crazily is slightly cheaper (if it arrives in one piece!).
Suggestions wlecome, but I need to get back on the road. Our Mopar Nationals is less than a month away and involves a 600 mile round trip for me.
A

 

[b_body_hopeful]

Sorry, IMO, purchase a new rad...I always do. The worst thing ever is to get on the road and have the car overheat. Very frustrating. I have no luck with older rads.

 

[UKPlymouth]

Yep, ordered a aluminium rad tonight plus separate trans cooler. Might be a shoe in to fit, but she will stay cool!

 

[bigredbird]

My 360/408 was overheating with a steel radiator when I got it. Switched to a 3-core aluminum and have been at a cool 200 degrees ever since.

 

[Dennis H]

Copper radiators work just fine. New motors do run hot the very first drive. Get a laser temp gun to be sure of the actual temperature. Leave 2 inches to the top for the coolant to reduce future burping. The guys at car shows with the puddle are the ones who can't resist "topping up.

 

[UKPlymouth]

Copper radiators work just fine. New motors do run hot the very first drive. Get a laser temp gun to be sure of the actual temperature. Leave 2 inches to the top for the coolant to reduce future burping. The guys at car shows with the puddle are the ones who can't resist "topping up.

Well, I'm set now as the ali rad has ben ordered. That said I now have somebody offering me a new spare stock rad so i will take both and see which works out.

Apologies for typos in my previous post, sat half asleep using my ipad without checking!!

 

[Cranky]

There's a lot of technical info on aluminum vs copper radiators on the net if you do some searching for it. I kinda like the aluminum ones myself but I also like the largest tubes I can find....

 

[Bruzilla]

I ended up buying an aluminum for my car but just because I didn't want to pay the insane prices people want for an original big block radiator.

 

[bm02tj]

never put dirty parts on a new engine now you need to clean and flush new block before new rad

 

[UKPlymouth]

I didn't put the dirty parts on. Long, long story about what I thought i'd bought and what I actually got!
I have a flush kit waiting.

 

[UKPlymouth]

Ok, story completed hope.
Fitted new 26" Ali rad, new thermostat (drilled small bypas hole in it), fitted a new Auto meter temp gauge and correct sender and went for a drive.
We have temp in the 80s plus at the moment and she never got hot either on highway or slow town traffic. Hottest I saw was 190 so I'll take that!

 

[BeastlyBirdie]

Not sure why you would drill a thermostat, if its a good, high flow, wouldn't need it. All drilling would do is create a bypass before its warm, and running an engine colder has its own issues.

 

[daredevil]

Not sure why you would drill a thermostat, if its a good, high flow, wouldn't need it. All drilling would do is create a bypass before its warm, and running an engine colder has its own issues.

Some do it as a safety measure in case it sticks and also so it purges air on initial fill.

 

[UKPlymouth]

I did the small bypass for reasons that Daredevul mentions. I've been riding a Buick Grand National for the past three years and the bypass tip is something I picked up off those guys. Those high powered turbo motors need to be kept cool and I thought it should apply to my Moar too.