Van overheating, ideas?

Richard · Jun 24, 2005

My Brother in law & wife are visiting. they have a van, unsure of make/model/year (and don't think that might really matter)

None the less, the van overheats & here's the symptoms

1. Sitting at idle, temp will be fine
2. Driving temp will get to hot range, turning heater on will QUICKLY drop the temp, evidently even while driving (fun in June huh? /forums/images/graemlins/shocked.gif)

I figure it's one of two things, radiator core or thermostat

My first line of guess is thermostat because at idle it won't overheat (slight water passage, low load). I think that if driving under load and turning the heater on would be sucking heat out of the engine (on the "inside loop" of the thermostat)

Then again, we had engine hot, (opened the radiator cap BEFORE hand) and the water was flowing NICELY in there, indicating thermostat is working fine. Also, there were intermittent bubbles popping out of the (removed) cap.

Every now & then, the water would "roil" out of the (removed) cap as though it was under some other kind of pressure. It would be all frothy, bubbly...and then seem to calm down to the traditional movement I'd otherwise expect from a properly working radiator.

So, that's the gist of what I saw. My first guess is sticking cap. The bad part is, this is one of those engines that are simply a PAIN in the hiney to get to, to work on /forums/images/graemlins/mad.gif

Any guesses as to which one is culpret?

There will be a prize for the lucky winner... perhaps a wapper off a pre-tested (eaten) hershey almond nugget? /forums/images/graemlins/shocked.gif

/forums/images/graemlins/grin.gif

Oh, I forgot to mention... I asked if radiator ever runs low (sucking water into heads, or dripping out of pump). I'm assured that it loses zero water. I'm taking that at face value.

Bird · Jun 24, 2005

I'm not mechanic, so can't say what it might be, but my first suspicion would be a radiator hose collapsing when driving. I'd be feeling the upper and lower hoses to see if they feel soft. Of course, I'd also check to make sure the fan belt is properly tensioned (depending on what the van is, it may have an automatic tensioner), and I'd try turning the fan by hand to see if the fan clutch is shot. From your description, I just can't see it being the thermostat or radiator cap. Good luck.

Oh, and if it is a soft radiator hose, you may be able to even see it suck together just by revving the engine after it's warmed up and with the radiator cap on.

Bigbear · Jun 24, 2005

You might check to see if it has an electric fan, sometimes the fan thermostat sensor (located down low on the radiator) will not work all the time. A water pump going out will also cause the same problem. And your correct, a sticky thermostat can cause this problem.

escavader · Jun 24, 2005

Squeeze the radiator return hose at the waterpump,while running .Is there pressure? a slight drip out the weap hole is a sign of a failing waterpump.Is it as simple as a loose belt? I would change the thermostat next,its cheap and easy.make sure you clean off all the old gasket,and note how it comes out.[the spring should be towards the block] If this dont help i might suspect the head gasket,is the rig running ok.[sometimes they will,sometimes they dont] I HAVE SEEN VEHICLES JUMP TIMING,AND OVERHEAT IS IT RUNNING RIGHT? ESCAVADER

PineRidge · Jun 24, 2005

<font color="blue">You might check to see if it has an electric fan, sometimes the fan thermostat sensor </font>

If this is the case and the van has air and you turn it on a relay will run the fan to keep the condenser & the radiator cool. It may get you by until the sensor can be replaced.

normde2001 · Jun 24, 2005

Unless the radiator cap is new, I would start by replacing it, just because it's cheap and easy. Next try a radiator flush. Sometimes that will free up a sticking thermostat. If anything like my van, I would probably get a garage to replace the thermostat.

Richard · Jun 24, 2005

Ok, just got back & thanks for the thoughts thus far.

All of the following is based on what he’s told me in part out of questions I’ve asked him and in part, filler commentary.

First off, this is one of those vans where the engine is BURIED and very difficult to get to (unless it has the removable hump inside and I don’t know yet.

1. He says it has a mechanical fan
2. He says he “knows” the water pump is fine (although we’ve not looked. Indeed, it’s near impossible to even see given how far it’s buried in the depths of the engine compartment)
3. The van runs like a top as far as I know
4. The water level has been constant
5. No indications of water in oil
6. No indications of steam out of exhaust

Update info: He put some kind of “coil cleaner” (for air conditioners??) in the radiator. Evidently it’s similar to “CLR” and is supposed to remove deposits. It foamed up like a volcano you might have made years ago (baking soda/vinegar). Some of the rods in the radiator seem to flow water & he thinks a couple others might be clogged.

My guess given is still thermostat.

I’ve suggested to him we go ahead & take them BOTH out tomorrow. Replace thermostat & TRY to get the radiator to a shop on Monday so they can clean it. He wants to leave for home on Tuesday (New Orleans and we’re currently in Knoxville TN). I told the wife it’s a lot safer for him/them to take it out to have it checked while HERE, rather than to have it go ka-put on them in Nowheresville, Alabama or Mississippi.

He’s out right now test driving it and me? I’m heading to bed!

mrcaptainbob · Jun 24, 2005

Good possibility that the home cleaning of the rad with that foaming may have dislodged enough gunk to have totally clogged more than several tubes in that rad. The flow rate would be enough to keep it cool at lower rpm's, but the higher up causes more demand than can flow through the remaining fins. I'd go for a pro rad flush. Still, as was suggested, check the hoses first.....

JerryG · Jun 24, 2005

Richard,
Another thing to check is the fan clutch if it has one. They need to be replaced somewhere between 60-100K. The more miles the less efficient they are.