Could be.
I bought a Spectra Premium radiator at Amazon for it.
Amazon Spectra Premium Radiator for 1999 Dodge Grand Caravan
Because both hose connections are on one side, I “think” that means it is a double pass radiator, but single row?
It is the exact same as the radiator that is currently on the vehicle that I installed years ago.
It may not be adequate. I never really checked the temps as carefully as I do now (with OBD2) so it could be that it always ran hot.
After all the time and money youve spent on this, why not just spend a few bucks more and change the radiator?
I have a new one on hand.
in previous posts I mentioned that I put a garden hose to the radiator and it seemed to flow with no restriction in both directions so I was hesitant to install a new radiator for that reason thinking it was likely something else.
I also observed it with the engine running (see previous post) with a thermal camera and I could see the hot water flowing through it. I wanted to rule out everything else because as mentioned earlier, the radiator isn’t really that old and the system has been thoroughly flushed.
That said, at this point I probably will.
Make sense?
It makes sense to put in some labor and change it. (Preferably not when it’s 98 degrees out)
Yep. That’s probably next, and then to a shop to have an exhaust back pressure test done.
On the plus side, I’ll have a road ready 1999 vehicle with few failure points that I can confidently travel with. 
Firstly, lets define overheating. At 16 psi, a 50/50 antifreeze water mix boils at 273 degrees fahrenheit. Unless your coolant temp exceeds that number you are not overheating.
Engine temps generally exceeding 250F are considered overheating AFAIK.
When this vehicle reaches 240F I ALWAYS shut it down to avoid damage.
The FSM specifies that the fans will go to high speed when coolant temps reach 224F
To see the temps continue to rise above 225F even with the fans on High and even when moving means it’s not shedding enough heat…or it is making too much heat and overwhelming the capabilities of the cooling system
Which is it?
Since “it seems” that having the heater on highest setting is the only thing that has shown significant cooling, I have to assume that the radiator is not doing enough. But is that because it is not working efficiently (which would be corrected with a new radiator) OR is it because too much heat is being generated in the engine (maybe due to a clogged CAT?
Since I have a new radiator on hand, that’s next.
I just have a gut feeling it’s not the radiator. I do hope my guts are incorrect.
But sitting for 4 years could have damaged the radiators internals.
Neither your guts or your definition of overheating is correct, in my opinion.
Lets see what others here have to say about your 273F upper limit.
Everything I have looked up disagrees with you on that.
Maybe take a moment to look this up?
Nearly every source I have Googled lists 220F as about the maximum normal temperature.
Sure, it can get a bit hotter but much over that is too hot normally.
At 273F you’d probably lose head gaskets.
Maybe you are thinking about oil temperatures? I don’t know.
Dodge Factory Service Manual for this vehicle
The reason I keep going back to the CAT is because remember earlier I said it isn’t passing emissions tests. The EGR valve was thoroughly tested. All the sensors have been replaced, the O2 sensor readings seem to make sense and it does feel a little sluggish. It only had 158hp when running perfect tho so a little hard to tell. If I could get to the rear manifold while the engine is hot I might be able to get a laser temp reading of the exhaust manifolds but the rear manifold is not easy to get to.
Tomorrow before I change the radiator I’m gonna run it by a local shop and see if they can test the back pressure.
Definitely could be the radiator at this point. But as I posted above, water flows through it both ways freely and I flushed it recently with Prestone coolant system flush. Maybe it’s still deteriorated just enough to lose a significant amount of it’s heat transfer ability?
Was that test repeated since the belt was re-routed? If not, the thermal image of the rad may look significantly different now.
Yes. I did the drive test again. It sounds crazy, but it made no significant difference? Seriously. I’m like WTH ???
I knew for sure that was it but it still did almost the same overheating maybe down 2 degrees?
I have no explanation. If the pump was running backwards I would guess that the coolant was just absorbing the heat (until it overheated)?
Ok, so today I finally removed the upstream O2 just to see if exhaust restriction had anything to do with it and guess what?
I drove it twenty miles…it never overheated. It is 97F out today and I had the AC on. Moving it never got over 213F. But if I sit at idle long enough it gets up to 221F.(probably normal as hot as it is outside today).
I did not want to change the radiator until after this test.
So I would assume there is an exhaust restriction. Probably the CAT since it is probably the original, (24 years old), but “could” be the muffler?
What baffles me is that there doesn’t seem to be any power increase that I can feel. I had expected it to be a bit peppier if there was any kind of exhaust restriction.
But an exhaust restriction makes sense because it is failing the Emissions test. The CAT is probably shot. The exhaust restriction probably just made it run too hot for the cooling system to keep up?
What’s weird to me is that when I sit a light for a good 5 minutes and it starts creeping up (temp) I would expect it to cool back down quickly once moving again but that’s not what happens. It takes about 4 miles or so before I see the temps drop. maybe because it’s so hot out today? Or maybe that’s “normal” ?
So I bought a back pressure test kit and I’m gonna test the back pressure of the exhaust at the manifold (upstream) before the CAT and then after the cat (downstream). I’ll post those results soon. I am learning so much and making this vehicle like new again so it’s all good.
Love this vehicle.
Removing the upstream o2 sensor reduces exhaust backpressure, true enough, but since it is no longer in the exhaust stream, it also may prevent the powertrain computer from determining what it thinks is the optimum air/fuel mixture. So the improvement you’ve noted could be due to one or the other or both effects. Measuring the exhaust back pressure makes sense at this point. Suggest to also ask shop to inspect the pre & post O2 voltage vs time signals using their scan tool. That test would confirm or disprove there’s a problem w/ the cat’s functionality.
I figure you’ll get it eventually
It seems Nevada545 was still correct.
I think the majority of the problem was the pump was turning the wrong way. (a duh moment)?
Along with a bad temperature Sensor I am replacing today. It may have been causing the fans to operate erratically.
Additionally, I may not have had sufficient coolant vs water in the system leaving the ratio of water a bit too high allowing some boiling of the coolant.
I have since completely drained the system and carefully installed 50% antifreeze and 50% distilled water.
So a bunch of operator errors along with a few faulty parts. It seems to be ok now.
Can’t thank everyone who helped for their assistance and patience.
Last Note here…for anyone with this vehicle…
Yesterday after I thought everything was all good, the problem came back.
But I found that the fans were only working intermittently…
Odd because I had just recently installed a brand new Fan Control Relay.
Well, that NEW Fan Control Relay was faulty and only worked sometimes.
So in addition to the above, the stupid new Fan Control Relay was faulty.
Replaced it and NOW all seems to be Perfectly Splendid.
I was re-thinking this issue the other day; i.e. whether removing a car’s thermostat could cause overheating? My current theory is that the answer depends on whether the car is configured with a non-bypass thermostat, or a bypass thermostat.
Removing a bypass thermostat could actually cause overheating to occur, b/c when that type is removed it opens a passageway that allows a portion of the coolant to bypass the radiator, when it wouldn’t be open if the thermostat (properly operating) was installed.
Removing a non-bypass thermostat wouldn’t cause overheating, b/c the bypass path allows the same coolant flow to bypass the radiator either way.
If you happen to have a 3rd Gen Dodge Caravan with a 3.3L engine…
Over time the overheating issue came back. I finally got around to replacing the radiator and at least for now, it seems back to normal. I had flushed the old radiator several times with top shelf radiator flushes and thought it was clean inside. I’m thinking now that sitting for 4 years or so damaged it internally, probably with corrosion.
I pulled a 1200lb trailer with it a few days ago up to 60 miles per hour and the temp while moving stayed right around 200F. I would say the heat rejection is where it should be now. I underestimated the loss of cooling due to the old radiator’s internal damage.
Probably seems dumb not to have replaced the radiator sooner but I had many issues since the car sat for so long and wanted to fix and repair everything else first since the radiator passed the “flow tests”, wasn’t terribly old and had been flushed well.
Also, ALWAYS be sure that serpentine belt goes OVER the water pump pulley, not under it.
