Overheating but only when keeping engine above 2k rpm

dgw8022 · Sep 20, 2007

I am having an overheating problem but unlike the typical while it's sitting at a red light mine is while I"m driving and if I have the car over 2k RPM once I keep it under the engine will start to cool itself off.

Any ideas?

I am going to try and flush this weekend I overheated last weekend and blew a hose and all this rusty nasty stuff was coming out so I'm sure that a flush would help.

I have a 3-row oem radiator with a puller electric fan with shroud from summit. I know that my thermo is working cause I popped the cap and I could see the coolant flowing.

rbohm · Sep 20, 2007

flushing the old coolant out is a good idea, also check the lower rad hose as it might be collapsing and blocking coolant flow at the higher rpms.

spirockp · Sep 20, 2007

When did you get the Electric fan? This summer I installed an Electric fan and shroud. Before the install of the electric fan my temp was 195 degrees on the highway. (I have a 195 Degrees thermostat). As soon as I installed the electric fan it went up to 205 on the highway. That must be due to the air flow restrictions. And yes my shroud has the corners cut out with the rubber flaps.

I am considering swapping out my thermostat to 185. Will that help or hurt me? I was told that wold make matters worse?

Peter S.

mikethebike · Sep 20, 2007

Have you replaced the thermostat? When an engine overheats at higher rpm it could mean your coolant is moving too fast to cool while in the radiator. You said you can see the water flowing but it may be stuck open. By chance is it a Robert Shaw unit? The only DOA thermostat I ever bought was a Shaw.
I've never seen a lower hose collaspe under internal pressure such as you would see in your system with a pressure cap. What I have seen is the hose collaspe when the coolant cooled after the engine was shut down and the pressure differential was reversed from hot. But that would not cause you to overheat at speed.
Since your system will keep up at lower speeds you can assume it has enough capacity, enough fan, and enough flow.
I chased this same problem in 1965 when I was 16 years old with my grandmothers 1960 Falcon. I had the radiator cleaned, new hoses/belts. It still got hot on the highway but not in town. Took it by Sox's Sinclair and Jake just laughed and told me to replace the thermostat. I did. It worked.
One other thing....do you have the hood seal that goes about the radiator? How about the rear seal? If you don't have these you will build prressure behinnd the radiator as you go faster and block the air flow. Put these in place before you go chasing other things.

blown65 · Sep 20, 2007

Suprised no one has said this but.

My cousin had his fan wired backwards once and well, it doesnt cool too well pushing air thru the radiator when your driving. lol

ratio411 · Sep 20, 2007

I lean to the lower rad hose sucking shut.
Get a new one, and make sure it has a spring in it.

Comment on previous post:
An engine with a thermostat in it at all cannot pass coolant too quickly.
That is only when running without a stat installed.
The stat just being present is a restriction. Even when stuck open, it will not over heat.

My second guess would be an issue with the electric fan.
It must be sending the air in the right direction, must be big enough for the task, must come on at the right time, and almost always needs a shroud.

CraigMBA · Sep 20, 2007

Unplug the fan and drive it around for a while.

TD68302 · Sep 20, 2007

Does it overheat in the driveway, running above 2000 RPM's, or just when you are driving.

Driving I would guess fan
Sitting I would say lower hose

66Coupe289POWER · Sep 21, 2007

You say there was a lot of rust in the coolant when it blew the hose? How old is the water pump? I have seen a lot of water pump impellers rust away to where they are just metal discs with little edges on it. It may be enough to keep it cool when there is no load on the engine but not enough while driving. Everyone I have seen with the impeller rusted away had similar symptoms as yours. Just my .02

ratio411 · Sep 21, 2007

TD68302 said:
Does it overheat in the driveway, running above 2000 RPM's, or just when you are driving.

Driving I would guess fan
Sitting I would say lower hose

When I blew 3 heads gaskets due to a lower hose sucking shut,
it was purely a driving event.
I didn't catch it because it wouldn't happen until the rpms came up some AND the engine was under load.
When I figured it out, I noticed that when revving in park, the hose didn't suck all the way shut... But it was noticeable at that point.

Also, when driving, you don't even need a fan over 45 mph.
Forward motion supplies all the air you need.
It's when you stop that the fan is essential.

So I kinda look at it directly opposite.

blown65 · Sep 21, 2007

ratio411 said:
When I blew 3 heads gaskets due to a lower hose sucking shut,
it was purely a driving event.
I didn't catch it because it wouldn't happen until the rpms came up some AND the engine was under load.
When I figured it out, I noticed that when revving in park, the hose didn't suck all the way shut... But it was noticeable at that point.

Also, when driving, you don't even need a fan over 45 mph.
Forward motion supplies all the air you need.
It's when you stop that the fan is essential.

So I kinda look at it directly opposite.

Trust me, when you have a puller fan, and you wire it as a pusher, driving at 45 the car will overheat from nearly no airflow thru the radiator. His did the exact same thing. been there done that.

ratio411 · Sep 21, 2007

blown65 said:
Trust me, when you have a puller fan, and you wire it as a pusher, driving at 45 the car will overheat from nearly no airflow thru the radiator. His did the exact same thing. been there done that.

Oh yeah!
I wasn't arguing that situation.
That is certainly a circumstance directly related to an electric fan.
My though process was purely based on knowing the fan wasn't doing that.

blown65 · Sep 21, 2007

Ya, it was actually kinda funny when it happened, cause he couldn't figure out wtf was going on.

twuxtop · Sep 22, 2007

?

what causes the hose to close? i (thank God) have never had that problem, and i dont have coils in my hoses. should i put some hanger wire in the hose? suggestions? thanks

dgw8022 · Sep 23, 2007

The water pump is brand new as well as the hoses which do have the coil inside them.

The fan is wired correctly because I can hold a piece of paper about a foot and half away and the fan will suck it right up to the radiator.

I'm really leaning towards just crap in the engine. It's an old engine I picked up off craiglist so I have no history on it but when the hose did blow I got most of the water in a bucket when I poured the bucket out at the bottom was this rust like paste rather nasty.

I'll do the flush first then if I still have a problem I'll have to think of something else.

Thanks for the replies everyone I'll keep you posted on what I find.

jeffnoel · Sep 23, 2007

ratio411 said:
Comment on previous post:
An engine with a thermostat in it at all cannot pass coolant too quickly.
That is only when running without a stat installed.
The stat just being present is a restriction. Even when stuck open, it will not over heat.

I disagree, I've seen cars with 160 thermostats installed that would overheat because coolant didn't stay in the radiator long enough to transfer the heat.

Usually someone with other cooling issues trying to fix it by running a colder thermostat but actually making the problem worse.

ratio411 · Sep 23, 2007

I have never had nor seen that problem.
I am in the deep south too, with very hot summers.
I run 160s on everything except my diesels.

If the car can't cool with a stat installed, then the radiator is not big enough IMO.
I was running a one row rad in my 302 pickup, with 160 stat.
It had trouble cooling, especially when in motion.
I went to a 2 row rad, and now it runs very cool all the time.

If you look at a stat, it is a pretty extreme restriction to the upper hose.
Even when it is open all the way, there is no comparision to having no stat.
Not even close.

jeffnoel · Sep 23, 2007

Deep south has nothing on Fresno, CA we typically have 20+ days over 110 in the summer.

What I was trying to say was installing a colder thermostat won't cure an overheating problem if there are other problems with the system.

ratio411 · Sep 23, 2007

jeffnoel said:
Deep south has nothing on Fresno, CA we typically have 20+ days over 110 in the summer.

What I was trying to say was installing a colder thermostat won't cure an overheating problem if there are other problems with the system.

Ah, sorry...
I agree.

bnickel · Sep 24, 2007

what is you water/coolant mixture? if you run more than 50% antifreeze the engine won't cool right, coolant is actually a misnomer it's just antifreeze but actually lowers the boiling point as well the freezing point. i generally try to run about 60-70% water and the rest antifreeze. a few weeks ago i got the mixture wrong after pulling the radiator to fix my fan cracked fan shroud, i put too much antifreeze back in and it ran hot all day, i drained some out and filled it back up with plain water and haven't had a problem since.

Overheating but only when keeping engine above 2k rpm

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