I am not a mechanic and have limited experience working on cars, but I'm trying to learn so bear with me.

I have a 1995 E150 5.8. Doing some regular maintenance that was clearly not-so-regular for the previous owner and flushed the coolant system – nasty. Replaced both the upper and lower radiator hoses, as well as the thermostat (I made sure it was in the correct way). Filled with 50/50 mix and bled the system both on my steep driveway and with a no-spill funnel. Coolant flow and level appears to be good. Van is fairly new to me and the temp gauge was pretty much at a standstill in the dead middle when I initially bought it.

I'm now having an overheating issue I wasn't experiencing before. The van drives fine for the first 15-20 min, plenty of power, no smoke from the tailpipe. Temp is showing a bit higher than before sitting around the M, it'll creep up to the A as I merge onto the highway, then "release" back down to hover around the M again. This will happen maybe 4-5 times as I'm driving, but then this "releasing" stops and the gauge slowly creeps upward until it maxes out around the H. It doesn't seem to want to cool down unless I turn off the van and let it sit. This same process happens every time I try to drive it.

I've been searching but wasn't finding much with these specific issues. I've been reading about thermostats being faulty out-of-the-box – I did not test the stat before installing, my mistake, so I'm thinking it might be that..? It's a Motorcraft replacement. The "releasing" of the temp back down to M seems like the thermostat opening as it should, but I'm not sure why that would stop happening after 4-5 times. Or if it's still opening as it should but is overheating from another issue. Thinking about picking up an IR thermometer to check the actual temperature and see if it might be sensor-related but wanted to see if these symptoms were definitive to someone more experienced than me.

Thanks in advance for any advice and I apologize for any newbie mistakes along the way. Ya gotta learn somehow.

 

How many miles on the engine??? It could be a bad T-stat, lord knows I've had a few bad ones right out of the box. It could also be the impeller on the water pump is failing, could be the clutch on the fan isn't working, it could be plugged fins in the radiator, maybe you have air trapped in the system?. You said it wouldn't cool down unless you pull over and shut off the engine. How long do you have to sit for the temp to get back to normal operating range? Have you tried turning the heater on full blast to see if it takes part of the heat away? are all the air diverters in place around the radiator?
Now that I've said all that....If you didn't have problems before the T-stat change, it's highly probable that it's a faulty T-stat.

 

Thanks for the thoughts. Really hoping it's just the thermostat.

118xxx on the engine. I've had it inspected before and after purchasing and everyone has said it's solid overall.

Like you mentioned, I had no issues prior to the change so I'm hoping it's not the water pump, radiator, etc.

I've bled the system on both a steep incline and with a no-spill funnel but I'll be doing that again to confirm no air before going further.

It takes maybe 15-30 minutes to have it cool back down, but I'm also in the middle of a heat wave so that hasn't been helping.

 

If everything was operating normally before you worked on it then it's going to be either a faulty thermostat, system is air bound, or the flush caused some kind of blockage.

 

You really do need to have an actual coolant temperature reading rather than relying on the dash "gauge" rather than citing "M", "H" and other obscure guesses what at what point the t'stat might be opening..

Typically a good quality t'stat doesn't need testing although that's not a bad idea to do especially if its a lesser or unknown brand of part. All parts are subject to be DOA but in this case since the dash "gauge" is showing activity I'm thinking this t'stat is working okay.

Install an actual numeric read-out coolant temperature gauge or buy the IR temperature gun, aim it at the t'stat housing and see what that reveals.

 

When you mentioned overheating it immediately made me think of Fan Clutch !

Before you go further: my advice is simply check your fan clutch.
Remove the fan clutch and pry the outboard end of the thermal coil strip loose from the groove in the body of the clutch unit. Next rotate CounterClockwise 180-degrees. If the clutch spins on the shaft CHUCK IT.
This is a good check of proper operation. (I just replaced 2 culprits. yep).

As mentioned prior, if your cooling system was operating properly before your Service-Job, then I would say you have dislodged crud and plugged your radiator core tubes. If so, my advise is drop it off at a radiator shop so they can check flow.

 

First get a no contact infrared thermometer and when the gauge reads overheat stop, open the hood, and take temperature readings at the t-stat housing and intake to see if it really is overheating to rule out an instrumentation issue. Then go from there. Maybe you just disturbed the temp sending wiring.

 

Thank you all for the input!

I picked up and IR temp gun and a new thermostat. Drilled two small holes in this one. Installed correctly with no leaks.

Fan clutch seems good? I was only able to spin it maybe 1 – 1.5 times and there was plenty of resistance.

I looked down into the radiator and saw a bunch of the core tubes seemed to be obstructed at the tops. I bought some radiator flush, let it soak, then backflushed just the radiator from the lower hose to the upper to try and dislodge any obstructions. Looked a bit better afterwards but I know that's not the whole story. Mine is a two row.The flow appears to be ok based on the rate of water during the flushes? Maybe that's a mistake to assume..

Also flushed the heater core/block again.

New coolant, done what I can to burp the system on my steep driveway with a lisle funnel. Not seeing any more bubbles unless the coolant boils over.

Unfortunately it's still overheating once I start driving. The IR gun is reading around 190 –194 at the thermostat housing while idling during the air burping, shows around the "M" on the dash. So I'm guessing that means the thermostat is operating as needed. Doesn't seem to overheat at a standstill unless I hit the gas.

Now I can drive maybe only 5 – 10 min before it maxes out. No loss in power, no visible smoke, no visible oil in the coolant. Temp gun reads around 230 at the thermostat housing when shown as overheating on the dash. It used to self-correct a few times with the first thermostat and eventually max out. Now it just maxes out almost right away.

I do have a spring in the lower radiator hose so I don't think that's collapsing. No visible leaks anywhere, no pools on the ground.

 

I have a 88 E150 with a 5.0 in it. Right after I bought the van, I flushed the coolant system and changed the thermostat. Shortly after changing the thermostat, the temperature gauge maxed out and then all of the sudden corrected itself. The new NAPA thermostat was sticking in the closed position but once it got hot enough, it did pop open. I ordered a Motorcraft 194f thermostat and don't remember just why but now have 2 of the Motorcraft thermostats. Anyway all of the thermostats are supposed to be 194f. I did not have a laser thermometer but put all three thermostats in a pot of boiling water and all three were opened different amounts at 212F. They did not even start to open until the water was getting close to boiling. So I do not think a thermostat starts to open till it reaches its rated temperature, at least not a conventions older style one.

If you had no problems before you changed the thermostat, it is very possible that you have a bad stat. I think someone mentioned that you could have dialoged something and clogged the radiator but I would try changing the stat again.

The fact that you read around 230F at the stat housing when the gauge showed the engine was overheating verifies the engine temp is far past the thermostat rating. I have a mechanical gauge on my van and I used the Motorcraft 194F thermostat that opened the farthest during my testing. Cruising along at 55mph on a flat highway with outside temps around 80F, my gauge reads between 190 to 195F. I have been pulling a trailer up long mountain grades on hot summer days and seen my gauge reach 210F which did have me worried.

I don't know about your 95 but my 88 has a copper/brass radiator and I took it to a radiator shop and had it professionally cleaned for about 100 bucks.
If yours is aluminum then you might be able to buy a new one for not much more then having the old one cleaned. But first I would change the stat again.

 

I'm thinking the thermostat might be ok given it stayed right at that 190–195 range when starting up and idling (before any driving)? My IR thermometer isn't top-notch (Harbor Freight) but it appeared to climb to 195ish and then drop back down to the upper 180's, then repeated. It seemed to be cycling right in that range, which sounds like its operating correctly..?

I do have a third thermostat coming in the mail that I ordered prior to installing the second, so I may test all three side-by-side and pick the best of the bunch if need be.

After the responses here I think that and a new radiator are in the cards. I'm going to try one last long funnel-bleed of the system in the morning to really confirm it's not just air, then move onto swapping those two out and hope for the best.

I'll admit – looking into the top of that radiator was not a pretty site. Brownish sludge, calcium deposits, random little pieces and sediments. If I'm going through the effort of removing it I might as well get a new one given the way it looks (and likely functions). I'm really hoping that what's been said here about the flush dislodging and clogging the cores is the case.

 

To any future searchers with a similar problem, it ended up being a clogged radiator. Replaced with a new one and now seems to be staying cool.

Thank you to everyone who shared their thoughts – I really appreciate it!

 

I just sent my radiator for my '78 460 and had it re-cored locally. The upper tank is an D8UH RA. mfr 11-77.
It was a 2-row core and i had a 3-row core installed. I wanted to stay with the copper / brass thermal properties.
Cost for the re-furb was $530.00, and I am very pleased.

Glad to hear you have your van running cool again.
Your old radiator may be worth selling to someone who wishes to get it re-cored !