Overheating but absurd.

[padgett]

For some time I've been fighting an issue with a more modern old car overheating but this is screwy and would appreciate ideas.

 

Car in question has been fine on the road but overheating when stopped. Electric fan and is on so no clutch to worry about but hose and rad felt cool so I replaced the thermostat (Stant Superstat in 180F), water pump (OEM), and plugs (was there). No change, fine when moving, rapidly passes 200 when stopped.

 

Finally I tried something stupid: raised 600 rpm idle to 1200 rpm. Temp dropped like a stone, rad and coolant hose up to temp. Let idle back down and temp heads to the moon. Hoses clear and not collapsing, passages clear and clean when I pulled the water pump (touch of weep at hole when pully was pulled so new was needful).

 

Only thing I can come up with is the coolant flow at 600 rpm is too slow to cool properly. Anyone have another ? Easy answer is to raise to idle to 900 rpm but tight torque converter already wants to creep at 600. Is there such a thing as an auxiliary water pump that only comes on at idle ? YWTK.

[Marty Roth]

Simple, relatively inexpensive but effective, and maybe dumb suggestion -

raise idle to 900 but slip into "N" neutral at each taffic light, or when forced to idle-

 

also - maybe a 160 F Stant Superstat - like I did for mine,

a bit less economy?

but runs a bit cooler

[5219]

Did it act like this before you replaced the water pump?

[Laughing Coyote]

Did you replace the radiator cap too?  Just throwing that out there. 

[padgett]

Yes replaced the rad cap (15 lb), yes acting like this since outside temp passed 90F. Originally started to just replace thermostat (didn't know about effect of raising idle then). Just escalated to water pump since questionable and spark plugs since was there. Now is evidently a water flow issue. Anyone ever use an auxiliary electric pump ?

[Hudsy Wudsy]

Quote

I have the vaguest recollection of someone having the same problem years ago.I think that it turned out to be an impeller problem - like maybe it was loose. If the engine has been modified from stock, maybe it has an incorrect size water pump pulley?

 

Edited September 10, 2019 by Hudsy Wudsy (see edit history)

[Ronnie]

Air lock? Water pumps don't circulate air very well.  See if you can purge air from the cooling system.

[padgett]

It is well purged (has a tap).

[Marty Roth]

Is your replacement water pump New or Remanufactured?

Dealer/Manufacturer, 

or aftermarket?

I've seen a new inexpensive aftermarket pump with an ineffective impeller,

and a ReMan pump with the wrong size impeller fins.

 

Just another thought -

did the new pump come with it's own pulley, maybe larger diameter than original, resulting in slower turning pump?

[wyankee]

Is there any way to use a smaller (circumference) pulley? That would speed up the water pump leaving the idle alone.

 

 

[maok]

See how it goes without the thermostat.

[SBlomquist]

Have you checked for good coolant flow through the radiator? The thought is that coolant pushed by the pump is up against more resistance to flow through the radiator tubes at the low RPM's. Remember the pump is not a positive displacement pump like the oil pump.

[joe_padavano]

8 hours ago, padgett said:

Only thing I can come up with is the coolant flow at 600 rpm is too slow to cool properly. Anyone have another ?

 

Yeah. Are you using ported or manifold vacuum for the distributor vacuum advance? Ported vacuum will be zero at idle, but as you open the throttle the ports are uncovered and the distributor sees higher vacuum levels, advancing the timing. Many cars in the late 60s had this problem with ported vacuum and automakers used a thermal vacuum switch that would switch the vacuum advance from ported to direct manifold vacuum if the coolant got above a certain temp. This advanced the timing and made the car run cooler. If your car doesn't use one or if it is not functioning or not plumbed properly, this could explain your situation.

[misterc9]

You didn't say what kind of car this is. They sell high performance pulley kits that slow down the engine accessories to cut down horse power loss used to drive them. The slowdown is most noticeable at idle. Maybe a previous owner installed a set. Maybe you could compare your pullies to another car like yours.

[Hans1]

check distributor base timing, and is Distributor advancing properly?

check counter weights and pivot points and springs.

Might be sticking.

Best wishes

 

[padgett]

Thanks but replacement was a premium pump and looks identical to original. Had a similar problem before I switched everything. Just seems flow is too low at 550 rpm and temp comes right back down at 1000-1200 rpm for appears to be a flow issue. Can't change the pully.

[John_Mereness]

On 9/10/2019 at 5:46 AM, maok said:

See how it goes without the thermostat.

Generally not a good idea as a thermostat is typically also a flow restrictor - coolant needs to be in a radiator for a certain amount of time to cool properly.  I would however drill a small hole in the thermostat's edge to allow elimination of potential air pockets and I would go with a 160 thermostat. 

 

Then I would play with ignition timing.

 

And,  a lot of knowledge on this website - always good to not talk in generalities and tell exactly what car is and ....

[Dashmaster]

padgett,

Not sure if you are talking about a Reatta or another car. Thoughts. You need to a way to verify temps. A thermal reading device might help to read host temps to see if they are inline with what the car is showing. Have you checked the Temp Sensor for Buildup that could cause errors in temp reading or any other issues with the sensor? Also the trans temp will cause temp rise at idle for the cooling system. Adding if not present a trans cooler may help.

 

[Rusty_OToole]

When I have run into this problem it was because of a partially clogged radiator. Before you buy a new rad you could check the old one with a laser thermometer. Look around for cool areas where the coolant is not circulating. The core should be the same temp all the way across.

[cheezestaak2000]

look into all of the above ideas AFTER you reverse flush the cooling system. sounds very much like restricted flow thru either, or both, the radiator , heater core.

[deane bruce]

After 45 years of auto repair on new and older cars, I agree with Rusty O_toole. These are symptoms of a restricted radiator. 

[padgett]

Thank you.

[maok]

10 hours ago, John_Mereness said:

Generally not a good idea as a thermostat is typically also a flow restrictor - coolant needs to be in a radiator for a certain amount of time to cool properly.  I would however drill a small hole in the thermostat's edge to allow elimination of potential air pockets and I would go with a 160 thermostat. 

 

Then I would play with ignition timing.

 

And,  a lot of knowledge on this website - always good to not talk in generalities and tell exactly what car is and ....

 

You wouldn't think it would be good quick simple experiment to see if this maybe the cause.

[John_Mereness]

14 hours ago, maok said:

 

You wouldn't think it would be good quick simple experiment to see if this maybe the cause.

I would never remove a thermostat - a cooling system is a very engineered thing.    What you find happens via ellimination is you solve one problem to create another - the car of course will warm up slower, but you often find people who have done so get erratic overheating in certain other situation (ex. after highway driving and then hitting a stoplight in town traffic).

 

I would quickly loose the 180 degree thermostat for a 160 degree though and I was taught real early on to drill a hole so as to allow some circulation matched to eliminate potential air pockets.

 

Sidenote:  Just because a thermostat comes out of a box off a store shelf does not mean it works correctly. I cannot tell you the number of times I have helped someone who is insistent that their new part works - and it does not. 

 

Best figure out what the real problem is and address that. 

Edited September 14, 2019 by John_Mereness (see edit history)

[John_Mereness]

By the way, I have seen some stupid stuff - 100 point painted radiators with no flow - someone accidentally put it in the wrong place in the radiator shop and they thought it had been boiled out. 

[padgett]

Back in the day we would replace the thermostat with a fender washer having a 5/8" hole in the middle. Just leaving it out would make a SBC overheat (flow too fast).