temp creeps up at highway speeds

[John h]

Hi All,
I have an issue where my temps stay cool, around 195 -200* while driving around town and even just idling for long periods of time. If I start driving on the highway, say 55-70 MPH, the temps start going up. The highest I let it get was 220*. I let off the gas a little and brought it down to 50 MPH and the temp immediately started to come down. I tested in a number of driving ranges and temp days. Same issue always. I read a lot of posts about this all over the internet, but unfortunately, people rarely post the fix. I Think I figured out my issue tonight but I don't know the reason for it or exactly what to do to fix it. at about 1500 RPM the lower radiator hose starts to distort. by 2500 RPM, it totally collapses. so basically all the cooled coolant in the radiator is getting choked off from getting back to the water pump and then is not circulated into the motor. Is the simple fix a new hose or do I potentially have a blockage causing the pump to pull way too much pressure?

Thanks in advance
John

 

[Rapidfire]

Should have a spring in the lower hose to keep it from collapsing!

 

[Chryco Psycho]

HI John where is your timing set , are you running vacuum advance & if so is it connected to manifold or ported vacuum ,
If you have the timing retarded it will heat , if you connect to mainfold vacuum with vacuum advance it will run hot ,
You need 14-16* initial timing with total timing around 34-38* & I never use vacuum advance & leave it disconnected .

 

[70chall440]

Get a new hose, I had a similar issue years ago and the lower hose was just wore out, but as posted, it should have a spring in it. Some of the "universal" ribbed ones work well too, very stiff.

 

[Steve340]

The spring is there mainly to allow vacuum filling in assembly plants. I have worked on hundreds of cars over the years that had no spring in the bottom hose. Think about it you have 15 psi in the cooling system so how can a hose collapse with 15 psi blowing it out/up.
Your radiator is partially blocked and that means not enough water flow through the radiator so the water pump collapses the lower hose feeding the water in to the engine.
A spring in the hose would not allow this to happen but it is not your core problem.

 

[John h]

Thanks for all the quick replies. My timing is controlled by my Fuel injection. I have 12* advance at idol and all in at 36* I had badly discolored coolant in the first run of the spring so I flushed it numerous times, with the hose and the radiator hoses off. Flushed it until it ran clear. Then I hooked it all back up and filled with distilled water and radiator flush chemical. drove for about 45 minutes and let it sit over night. Flushed again with water, filled up with distilled water only and drove again another 45 minutes. drained the distilled water and it was still discolored, so I started the process over again with new distilled water and radiator flush. after all that, i filled with 50/50 mix anitfreeze and distilled water. (mixed myself). I check the temp with a IR heat gun at the top of the rad and the bottom outlet. they are 15-18* different so it seems the coolant is getting to the bottom cooler as it's supposed to. I will look at different hoses and see what's available. It seems I have plenty of cooling capacity in the Radiator. It's a 26" core because the car was factory air, even though it was a 318 small block when it was born. The Engine is a very mild crate 360. If the new hose is no help I will look into having the radiator rodded out (if they still do that in these days of disposable everything) in case of a large blockage.

 

[CudaChick1968]

Are you using a fan shroud?

 

[Ccas]

What gears do you have? What rpms at 65mph?
1. spring in lower hose- first and easiest option However, a lot of time, it's collapsing because the heat is getting too high.
2. Timing
3. Make sure you don't have obstructed air flow. Sometimes high speeds create air flow blocks. Air can be coming up under or the side of the radiator and preventing maximum air flow through the radiator.
4. your radiator may be getting tired or you may just have made changes over the years that have exceeded the highway capacity of your radiator. Additional volume in your system ALWAYS helps reduce highway temps
5. The start of a head gasket leak. do a chemical test just to be sure this is not the problem.
There could be other reasons but those would be so rare it's not worth mentioning until you've dealt with these other much more common solutions.

 

[John h]

Are you using a fan shroud?

yes, factory shroud, fan and under hood rubber seal to the top of the radiator.

 

[John h]

What gears do you have? What rpms at 65mph?
1. spring in lower hose- first and easiest option However, a lot of time, it's collapsing because the heat is getting too high.
2. Timing
3. Make sure you don't have obstructed air flow. Sometimes high speeds create air flow blocks. Air can be coming up under or the side of the radiator and preventing maximum air flow through the radiator.
4. your radiator may be getting tired or you may just have made changes over the years that have exceeded the highway capacity of your radiator. Additional volume in your system ALWAYS helps reduce highway temps
5. The start of a head gasket leak. do a chemical test just to be sure this is not the problem.
There could be other reasons but those would be so rare it's not worth mentioning until you've dealt with these other much more common solutions.

I am running 3.55 gears. 16" dia rims with medium profile tires. would need to look into the conversion to get the exact diameter. standard 727 trans rebuilt with the radiator cooler. I will for sure address the hose collapsing. finding a new hose was easy locally, looks like a spring is going to need to come from an internet retailer. collapsing hose would be good to fix either way. I'm also going to replace my Rad cap.

 

[tonysrt]

Sometimes we overlook the basics, make sure fan belt isn't slipping.

 

[John h]

Sometimes we overlook the basics, make sure fan belt isn't slipping.

very good idea. I thought of that too but when I was last poking around I forgot to check the tension. When I found that the Rad hose was was collapsing, I got tunnel vision on fixing that issue.

Thanks!

 

[moparlee]

John, are you running a fan clutch? If you are, it could be slipping. If you are not, you should get one.

 

[John h]

John, are you running a fan clutch? If you are, it could be slipping. If you are not, you should get one.

I'm not sure if my fan is direct drive or not. I'ts the stock fan from 1973. it turns as soon as the crank turns. I think it was turning when I tested how many RPM it took to collapse the lower radiator hose.

 

[moparlee]

I'm not sure if my fan is direct drive or not. I'ts the stock fan from 1973. it turns as soon as the crank turns. I think it was turning when I tested how many RPM it took to collapse the lower radiator hose.

Here is what a clutch driven fan looks like.

 

[Ccas]

Here is what a clutch driven fan looks like.

that sure looks like a nice setup. That clutch and fan combo should be great for stop and go driving where not surprisingly, you are not having any issues.
The belt looks tight but if it was slipping, they get really slippery from the heat generated from the slipping.

 

[tonysrt]

I notice your P.S. belt hits the pump pulley just like mine. Although I have a gen 2 hemi, I guess the B family has that problem.

 

[moparlee]

I notice your P.S. belt hits the pump pulley just like mine. Although I have a gen 2 hemi, I guess the B family has that problem.

That happened one time when the belt wasn't tight enough. Normally it is ok.

 

[busterone]

Hi All,
I have an issue where my temps stay cool, around 195 -200* while driving around town and even just idling for long periods of time. If I start driving on the highway, say 55-70 MPH, the temps start going up. The highest I let it get was 220*. I let off the gas a little and brought it down to 50 MPH and the temp immediately started to come down. I tested in a number of driving ranges and temp days. Same issue always. I read a lot of posts about this all over the internet, but unfortunately, people rarely post the fix. I Think I figured out my issue tonight but I don't know the reason for it or exactly what to do to fix it. at about 1500 RPM the lower radiator hose starts to distort. by 2500 RPM, it totally collapses. so basically all the cooled coolant in the radiator is getting choked off from getting back to the water pump and then is not circulated into the motor. Is the simple fix a new hose or do I potentially have a blockage causing the pump to pull way too much pressure?

Thanks in advance
John

 

[busterone]

Did make sure you thoroughly burped the cooling system to get all the air out?