temps rising at HIGHWAY speeds?

jaymac

New Member
Feb 18, 2004
995
0
0
Northern Mass
I ususally cruise around town @ 180ish, and about the same on the highway, but yesterday I got up to about 195 on the highway, then it cooled down to 180ish again once I got off the highway.
I have 4:10's and and AOD, so I turn about 3 grand @ 75. I don't know if that would affect temps.
For those that don't know, the temp gauge is an new Sunpro. I recently had a leak that I fixed by replacing my overflow tank so the level is OK now, I just flushed and filled the system a few months ago, but will do it again, as the heat is not so good anymore.

Now, I do have a radiator that I bought for one of my mustangs about 6 years ago that I saved when they junked the car, as it was bought new.
My rad. now is a little rusty and sshiitty in places.

Does this rising at highway speeds seem more indicaitve of a rad. problem or water pump? As some of my most recent posts indicate, I have a slow leak in my water pump gasket, and am thinking about replacing the pump and the gasket anyway.

The fan clutch is also new.
Thanks guys,
J
 
  • Sponsors (?)


are you sure there is a problem? The stock thermostat is 195, so sounds like its working exactly like its supposed to. If you dont like it (i didnt like it myself), get a lower temp. thermostat and see that it doesnt get as high?
When I was in FL I went all the way down to a 160 cause of the weather, it was great for that, now im up north and am switcing it back up
 
J, that isn't too warm. Over 230 is hot...

Do you still have the air deflector on the bottom of your car? [the black piece of plastic near the radiator]

If your radiator is clogged, your car would over heat, but not just on the highway. Same would go for the water pump.
 
alright, thaks for the re-assurance, guys!
I do already have a 180* T-stat, which I why I wondered why it would go to 195*, and only on the highway.
I do still have the deflecctor in place, and I will check the coolant level again, just to make sure.
Thanks again~
 
also try burping the system. air gets trapped in there and that heats up more than the water. and check the ect on top of the intake. but running 195 at 75 mph is actually pretty good. im at 200 at 70 mph. and im running brand new autometers.....just my .02
 
Mine is the opposite.

When I am in stop and go traffic it warms up but once I get moving it cools down to 180. Even on the highway at 70 which is turning about 4k rpm, no OD anymore, the car might warm up to 185-190.
 
The only time I've ever seen problems with overheating at highway speeds it's been caused by poor coolant flow through the cooling system. Either because the water pump isn't pumping properly (not likely with a stock style pump) or because of a blockage in the system.

When was the last time you backflushed the cooling system?
 
Yeah, he said he still has his deflector / divertor for the radiator.

What if his car was just heating up from the increase in oil temperatures caused by the extreme combustion temperatures that the 5.0L is prone to...? I mean going down the highway would mean that his motor is firing at least 2,300 times a minute and maybe that heat is transfering into the oil (without an oil cooler, where does it go) Then into the block and to the coolant...

I bet that is what is happening here.
 
70_Nitrous_Eater said:
When was the last time you backflushed the cooling system?
My suspicions exactly. My heat isn't hot anymore, and last time that happened I backflushed the heater core and it spewed brown CRAP for 5 minutes straight, then the heat was the balls! I have to back flush it again, but I also want to drain the block this time. Anyone ever done that? I've read in the manual you're supposed to do it, but I've never drained the block during a clooant change.
I'll prob. throw that new (old) radiator in also, just to eliminate the corrosion and build-up.
JT, I do have the spring in the lower hose. I took the time to cut it out of my stock hose and snake it into the new one during my initial head swap.
 
Mine has done this same thing for as long as I can remember. And while I don't have the air deflector on anymore, I just flushed the coolant system when I did my heads/cam a few months back. I always thought it was strange, but it's never overheated, so I haven't worried about it. :shrug:
 
i have noticed the same problems with my car but only when its hot outside. When its cold it runs perfect...but i took that deflector thing off. Do u think that deflector makes that big a difference?
 
That deflector makes a real big difference. My car consistently heated up while doing highway driving when the deflector was off my car (I bought it that way). It took a long time to realize what the problem was. Now I drive on the highway and the car stays at 180* (t-stat temp) and the electric fan doesn't run unless I'm in stop and go traffic.
 
yep, the deflector is a good thing. It helps create a low pressure area behind the radiator so that the air that has moved across it has a place to want to go. This allows more air to want to be pulled across the radiator.
I just got done doing a kind of custom one to replace the wavey thing that was there before.

Good luck.
 
Out of curiosity, how do you backflush the system. My car has been doing the same thing for a while as well. The second I come off the highway it will cool down as much as 20 degrees sometimes. I was told about the spring in the lower rad hose might also be the problem.

I still wanted to flush the cooling system before winter came, so thats why I ask. I would like to backflush it to see if it would help at all.
 
redterror302 said:
Out of curiosity, how do you backflush the system. My car has been doing the same thing for a while as well. The second I come off the highway it will cool down as much as 20 degrees sometimes. I was told about the spring in the lower rad hose might also be the problem.

I still wanted to flush the cooling system before winter came, so thats why I ask. I would like to backflush it to see if it would help at all.


1st step is to pull off the thermostat housing and remove the thermostat. Put the housing back on in a temporary mannor.

Then pull off one of the rad hoses. They sell a fancy gadget that allows you to conect a garden hose to your rad hose...but I have always just stuffed the garden hose about 1ft down the rad hose and then wrapped it up tight with a rag to prevent as much leaking as possible.

The idea is to flush the system with water, but also do it so that the water is flowing throught the system in the opposite direction as the coolant flows. This helps to make sure all of the gunk is removed.

Then just turn on the hose and wait until you get nice clean water spewing out the other end.