1990, E150 5.8L FI . I know you can't really go by what the Temp gauge does, but it's a pretty good indicator. When the temp outside is is in the 80's and hotter. The van run well and stays within normal range on the temp gauge as long as you're moving. If sitting at a stop light for longer than two minutes the gauge starts creeping up. It hasn't hit the red zone yet but it gets close. I've change coolant, I've changed, the Radiator cap because I had seen the coolant leaking out on the ground after I parked the van. I temporarily wired up a universal overflow bottle and ran the overflow tube to it. I recently changed the serpentine belt because it was at the end of its adjustment and it was fraying. I cleaned out radiator fins and the condenser fins and made sure nothing was between the two. The only thing I can think of is the T-stat sticking or the water pump impeller is worn out or the fan clutch is bad. How to diagnose a bad clutch? Spin and get resistance is good? or no resistance is good? Should I just change the T-stat? The water pump looks like it's moving water, the shaft doesn't have any play and it's not leaking out of the weep hole so I really don't want to change it if I don't have to.
Your thoughts are appreciated. Thanks.

 

-Is the radiator shroud still in place?

-If the shroud is missing that can cause hot running when stationary.

-Looking down into the radiator, is there scale buildup?

 

The Shroud is in place and there is no scale that I can see inside the radiator. When I changed the coolant, I didn't do a flush I just drained and got as much out as I could. I didn't see a bunch of dirt or anything in the coolant. Heater works great. I used Prestone 50/50 Green color.

 

Have you been thru several run/cool-down cycles to see if you're losing coolant ?

A system pressure test would be good.

 

It's been through several cycles, and the res bottle get's about 1/2 - 2/3rds full. I don't have a pressure tester, I'll have to stop by the auto parts store to rent one or buy one. but since I installed the overflow bottle, I haven't lost any coolant.

 

You could temporarily remove the T-stat to eliminate that as the problem.

Might as well go ahead and replace it though for the work involved.

Check below for fan clutch info:

https://www.aa1car.com/library/cooling_fan_clutch.htm

 

I'm gonna lean on the Fan clutch not kicking in while sitting stationary at stop lights.

If that engine has been overheated in the past, then you may have stretched head bolts.
I just went thru that ordeal back in 2022 / 2023, until the weak headbolt (broken) got replaced. Now all is well again.

Edit at around 3:40pm:
The upper tanks on these engines are tall to allow for expansion of coolant as it heats up and expands.
The necessary air cushion gets compromised if over filling the system.

Example: the upper tank on my '77 jeep cj-7 with the AMC 304 V-8 engine is Shallow.
So, after careful measuring, I discovered the happy coolant level after shut-down (cold), is almost 1-inch below the top of the vertical tubes in the core. Amazing. If, I add any more than that, then the excess coolant gets pushed out the overflow tube.

I added a coolant recovery bottle, and when the broken head bolt lost it's clamping at 230-degrees, the combustion pressure just blew the coolant out the top of the recovery bottle. It was almost like an explosion. LoL
With the broken head bolt replaced, no more coolant belching and the system is behaving.
The '90 may have some sort of coolant temp sensor that could be giving you fits.
Good luck.

 

I sure hope that's not the case. There is no room in that engine compartment. The plenum is about 1/2" from the bulkhead. It's almost impossible to even do a plug change.

 

Fans often leak out the fluid from them that engages them, they don't last forever, you can tell when the engine is hot, shut it off and give the fan a spin, if you feel little to no resistance its bad, I had a mechanic once grab my fan and have me start the engine, I don't suggest that test tho.

 

No I am not going to try to grab the fan...lol. I'll check it this week hopefully.

 

That guy was crazy, was on my v8 Dodge Dakota, even with all the repairs, still the AC blew warm in traffic, too much engine in the engine bay, not enough radiator.

 

Getting a little cold out now so unless we hit close to 70 I doubt the needle will raise to far over to hot.

 

Still in the 70s here, winter seems to be on hold.

 

We're in the mid 50's the rest of the week dropping into the 30's at night. I still need to get 2 oil changes knocked out before snow hit's but it's been raining and I have no garage.