I have a slant 6 with a fresh engine build, coolant passages have been flushed many times, there is clean water coming out of the drain hole when I flush the system.

This car has the OE Radiator, it has been cleaned and checked at the radiator shop and also "rodded out"
A new 195° thermostat was installed during the rebuild.

The car will run around town, in stop-and-go traffic, and idle with no issues, as it does not get hot.

However, during sustained high-speed highway driving, the temperature begins to climb when going 70 MPH or more on flat no-grade highways.


Any Ideas for a solution?

Thanks,

Greg

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Radiator hose collapsing at higher RPM? Fan shroud?


Overheating at highway speeds is usually a coolant flow issue.

There is no fan shroud on this car.

I have no Idea if a hose is collapsing, but I could find/ buy a hose with the spiral spring on the inside and install it into my hoses.

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You didn't block off the grille or anything did you Greg? That sounds like an airflow issue to me.

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Official Cookie and Mater Tormentor.

No the grille is stock, and open. I have to pull the rad off today to replace the broken harmonic balancer that came apart on me, so I am going to try and find a sping to put up in the lower rad hose. Maybe it is collapsing on sustained high RPM as Reed had suggested? I have no way of telling if this is happening, but it's worth a try to slide a spring up in there to see if it initiates a wanted result.


Greg

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The simplest explanation is probably the right one: the OE radiators were no more than adequate when they were new. Rodding out can clean the tubes, but cannot restore the gradual/progressive loss of heat rejection capability as the tube-to-fin solder junctions degrade with age. Have the rad re-cored with a high-efficiency core (or do like this) and have done with the problem once and for all.

'Collapsed rad hose' is largely a myth. The upper hose would never collapse, and the only reason why the lower hose could collapse is if there is severe clogging or restriction in the radiator or thermostat—and the hose would then un-collapse once the system heats up and builds pressure.

A fan shroud helps with low-speed/idling/stuck-in-traffic heat-up; it is of no consequence at high road speeds. About the only fan-related potential cause of high-speed heatup is if the fan be installed wrong way round.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Your link didn't work Dan?

Greg if you want and "original " look then this won't apply. But the 3" crossflow I put in the race car works super good. I have run 5 or 6 back to back runs at Wilkesboro in 95+ weather and had zero cooling issues. If I am moving at all the electric fan never turns on.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Yes I want a largely original look with this one. Cutting the rad core support for this project is unacceptable.

I look forward to your link Dan.


Thanks Guys!

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Interesting. I actually had a radiator hose hose that would flatten out at higher RPM and restrict flow and lead to overheating. I don't doubt it is uncommon, but it can happen.

Oops, I hate it when I do that. Fixed now. Might or might not qualify as "largely original look", depending on your criteria. Paint the brackets and tanks black and you're about 90 per cent of the way there. If you gotta-gotta-gotta keep the original roundtop tank with the "MoPar" imprint and everything, what goes along with that is difficulty getting/keeping a good solder joint between top tank and core.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I don't claim it can't happen—only that it is exceedingly rare and has one specific cause. Think it over: that hose runs from the radiator outlet to the water pump inlet. The only way for there to be negative pressure in that hose is for there to be extreme restriction upstream of that hose so the water pump pulls a vacuum, and the hose would have to be weak/soft, and there'd have to be no/low pressure in the system as a whole.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I am with Dan's idea about the radiator. Also, I assume you have an aftermarket gauge, or you are measuring the temperature somehow other than the stock gauge? If stock gauge, it could be a whole lot cooler than you think.

Lou

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Home of Slant6-powered fun machines since 1988

It is a stock gauge.

I will throw a second mechanical gauge on there too to monitor it as well.


Greg

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Exactly. If memory serves, the specfic vehicle that had the hose collapsing was my sister's 2003 Buick Rendezvous It was factory filled with Dexcool which had the tendency to eat the rubber and gasket material of the engines it was put in. Ford used Dexcool for one year, 1999, and then abandoned it due to its gasket eating properties. Shortly after that radiator hose failed, I had to tear the whole top end of the motor off to replace failed intake manifold and head gaskets that began leaking coolant. When I put the engine back together I ran normal old ethlyene glycol. THe old hoses I took off that Buick were the softest hoses I have ever encountered on a vehicle. The pliability was comparable to a latex glove when the engine was hot.


I also concur that Greg should try a mordern radiator.

Ugh, DeathCool. Yes, it eats gaskets—very aggressively. Unfortunately, that is personal experience talking. Fortunately, the car was under a service contract, so I was spared the money costs.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.