Started Overheating

[JedIEG]

My car overheated the other day on a 20 mile drive to a show. ~85° out with the AC on. I have only ever had an issue with overheating once last summer and it was the t-stat then but not this time. I swapped a new T-stat in the parking lot the day it happened to get us home and it still overheated, I tested both the t-stats and they opened fine in boiling water.
I ran the engine at high idle with the ac on this weekend with no t-stat in after flushing the system 6 times and the temp still just kept climbing. I got to 180-185° in the upper tank, 160-165 in the lower tank and decided to stop. My thought is that the system should be able to keep the engine below that ( below 'C' on the gauge) sitting at idle as that was how it ran in the past with a 160° t-stat in when I lived in a hotter state. Something has changed and I have no idea what or why.


My suspects are in order
1) Clogged radiator
2) failed water pump
3) failed fan clutch

I bought new parts to replace all of them

Any suggestions would be great.

 

[TT5.9mag]

A 20 degree delta across the radiator is nowhere near enough for a system with AC and any amount (more than stock slant 6) horsepower. Either you’re not flowing enough coolant, or the Radiator is clogged.

 

[JedIEG]

Thats what im afraid of. It either has to be pump or radiator. The coolant didn't look great but I didn't think it was clog worthy. There is definitely coolant flowing that I can see with the cap off.

I have a new 26" ECP radiator that I was wanting to upgrade to when I get my new engine built but I guess I'll just stick it in for now. This engine was fine with a 18" radiator for 92k miles before it got swapped into my car. It had been fine with this 22" until now.
I got a cheaper waterpump to swap in so I don't have to use the new Melling pump I got for my engine build.

I just don't like throwing parts at a problem without knowing the root cause. I don't want this to happen again or damaged the new radiator.

 

[TT5.9mag]

Thats what im afraid of. It either has to be pump or radiator. The coolant didn't look great but I didn't think it was clog worthy. There is definitely coolant flowing that I can see with the cap off.

I have a new 26" ECP radiator that I was wanting to upgrade to when I get my new engine built but I guess I'll just stick it in for now. This engine was fine with a 18" radiator for 92k miles before it got swapped into my car. It had been fine with this 22" until now.
I got a cheaper waterpump to swap in so I don't have to use the new Melling pump I got for my engine build.

I just don't like throwing parts at a problem without knowing the root cause. I don't want this to happen again or damaged the new radiator.

Well you did the testing, you know the efficiency of the radiator isn’t enough by your temp measurements. To me it seems you’ve found the root cause and aren’t just throwing parts at it. As long as you verify that coolant flow is “enough”.

 

[Dana67Dart]

Well you did the testing, you know the efficiency of the radiator isn’t enough by your temp measurements

The delta of the rad is also the delta of the engine. At idle there is not a lot of heat generated.

So 20 at idle MIGHT be ok.

Have you checked for flow in the radiator?

 

[TT5.9mag]

So 20 at idle MIGHT be ok

Disagree.

 

[JedIEG]

I was expecting to see cold spots across the radiator with the IR temp gun but its seems pretty uniform so that is what has me questioning the radiator being plugged.

The opposite logic for the waterpump not working- If the flow is too low shouldn't the temp difference between top and bottom tanks be really high due to the coolant dwelling in the cooling tubes? That doesn't seem to be the case so that points toward the radiator being plugged...

It's the original 22" that came with the car so who knows the service life it lived. It's just the sudden overheating issue that has me puzzled. You would think a clogged radiator would slowly get worse over time, not be sudden.

 

[Inertia]

I was expecting to see cold spots across the radiator with the IR temp gun but its seems pretty uniform so that is what has me questioning the radiator being plugged.

You researched well, thank you.
You have circulation seen with the cap off, we know the rad isn't shedding heat near what it should, so rad is logical conclusion.
2 hose clamps, 2 top bolts, the 2 bottom bolts are slotted, so loosen them a coupla turns, carefully pull rad straight up.
Before heat guns, I used to drag my knuckles slowly across the front of rad, 1/2 way down, and often could feel cool areas.
Good job.

 

[Bewy]

Remove lower rad hose.
Shove some rag in the rad lower outlet.
Fill rad with water.
Remove rag. Watch how quickly the rad empties. If it is slow, you probably have blocked rad tubes. This is not a definitive test, but it might give you an idea.