99 EB, 4.6L 157K... (Long write-up, but trying to give as many details as i can)

The engine has overheated the last few days of driving (95f last few days).

From a cold engine it takes about 10 miles/30 minutes to overheat in town (up to 55 mph) When the temp starts to rise, dropping the engine into 2nd gear/reving the engine at stop lights..... definitively lowered the temp back to normal. Stopping at lights would make the temp raise, and after getting up to speed.

When it overheats, upper radiator hose it hot and sometimes very, very stiff. Sometimes when it cools from overheating the upper hose is collapsed, and there is a vacuum in the system that is relieved by removing the coolant bottle cap.

I replaced T-stat a few months ago, and the upper radiator hose always seems hot after warming up.

I ran super cleaner and flush through the system several months ago, added a prestone flush kit, (with the water flowing into the flush kit input)...flushed water from one of the block drains, removed the upper hose and let water back flow from the radiator, drained the radiator out of the draincock. removed the t-stat and let water flow from there... and let water backflow out of the coolant bottle... basically back flushing the system from every point at least 15 minutes each way.

Also the fan is crankshaft driven (not electric), and the fan clutch is very stiff (not free-wheeling) when cold, and very stiff when the engine is warm or hot... I assume that is should slip (free-wheel) when cold and spinn with the crankshaft when warm to hot.

I have not noticed lower coolant levels or the engine using water, except after an overheat ( water bolining off).


Any ideas?

I am not suspecting the T-stat, since the upper hose always gets hot after warming up.

Maybe a plugged radiator? Since the upper hose gets really hot and super stiff, maybe the tubes are plugged.

Maybe a failing waterpump? original pump..... and since the cooling seems to be affected by RPM, at least until it got really hot.

Maybe the fan clutch? i think normal operation is to free-wheel when cool and turn with the crankshaft when hot...

 

Sounds like a fin or two has broken off the water pump impeller, causing a reduced coolant flow. This reving of the engine temporarily compensates by increasing the flow.

 

Place my money on a restricted radiator. The upper hose is stiff because at the higher temps the pressure in the system is (should be) equivalent to the overflow bottle's relief pressure.

After it gets hot, run it a ~2000 RPM for a few minutes, then shut it down and see if you can feel the radiator fins in different places. If you can find hot spots and warm spots, I think your radiator is causing the problem.

 

1. are you sure the t-stat is installed properly?2. your fan blade should free wheel3. as mentioned, your water pump may be having some issues
this is one of those things that sucks to chase down...rarely do I recommend throwing money at a problem, but this is one of them.



the most economical fix might be to snag all the stuff from a junkyard at 1 time from a decent donor Expy...and at 157,000 miles...all that stuff has led a full life

 

KR1,
My 99 Expy did the same thing at 153k. Turned out it had the middle rows of radiator plugged up. After the engine warm up and the thermostat open, the radiator's top and bottom rows felt hot but the middle rows were cool.

 

All,
I replaced the water pump and T-stat yesterday..

ALLORO: Water pump fins were all ok, but the waterpump did have some erosion on the base, and looked like it had leaked some.

PDQFORD: Your correct, restricted radiator.

TYLUS: T-stat was installed properly. Fan does not free wheel. T-Stat was install correctly (spring side down)

KHANGMAI: I checked the radiator and the middle section is hot the top and bottom 1/3 were cold…

Priced a new radiator at Autozone was $180.

Is unclogging the radiator a DIY job?

 

Only $138 from here:
Radiator, Radiators: RadiatorExpress.com. Car radiators, auto radiators, radiator replacements, Radiator Express

I've used this place several times, 24-48 hours delivered right to my door.

 

Thx Alloro, i ordered one.

Like everything else that breaks, i will dissect it and try to post some pics.

 

how did you find out it was the rad?

at least it sounds like you've got it covered now

 

The upper hose is still somewhat stiff (functioning waterpump, stopped up radiator) and Hot (T-stat is letting the hot stuff flow). Felt the front of the radiator, top and bottom third are cold..middle is burning hot.

Fan clutch is not spinning freely, so will probably replace it since i have it tore apart..

Maybe all of this will help me get some more miles out of the green beast.

 

How do i remove the lower radiator hose from the radiator? I disconnected the power steering line and some of the fluid dripped on top of the hose fitting where there were instructions on how to remove. I wiped the fluid off and the words.......

there is only a slip type fitting, so i assume that i need to twist and move side to side ?

 

There is a little metal tab that you have to bend back. After that, twist the hose 45 degrees counterclockwise and then pull with all your might.

 

Make sure you get a new radiator cap too.

 

i found it easier to remove the radiator with the lower hose still attached to the radiator, but disconnected from the engine...

i did replace the cap.

Works good now, heat is evenly distributed over radiator from top to bottom...

Note; the power steering lines were burning hot... is this normal? fluid level and function is normal.