So, I have been having a sporadic overheating issue with my 1998 Disco for the last year. The car can idle for hours without overheating, but will occasionally overheat after I have been driving for awhile. Sometimes turning on the heat solves this, sometimes it doesn't. Because of this I have not driven it much in the past few months, however, I recently decided to fix it up so that I can sell it, so I brought it to a mechanic to look at the overheating issue as well as a couple of other minor issues. I drove the truck for about an hour before bringing it in and it got hot (high end of acceptable on the gauge, not in the red but close), at which point, I pulled into an Autozone parking lot and walked inside to let it cool down (incidentally, it was an extremely hot and humid day) and while I was inside I looked out the window to see smoke pouring out of my disco which had already been off for about 5 minutes. Turns our the heater core line blew and has spraying antifreeze everywhere. I replaced the hose in the autozone parking lot (fortunately) and refilled it with antifreeze, however it overheated again after idling for about 10 minutes, which it has never done before, so I had it towed to my mechanic.

Here's what has already been done at this point... Thermostat has been replaced twice, water pump has been replaced, coolant system has been flushed and properly bled of air... still overheats.

Mechanic says the system is building up pressure rapidly which is leading him to think that it is a head gasket issue or a plugged radiator... however he does not have the equipment to actually test the engine to know for sure. (this is my first time using this guy, so I don't know how much to trust him) Also, he said the fan clutch is shot but he doesn't think that is the problem (this seems odd to me). Also, my friend threw out the idea that the lower radiator hose could be collapsing under load and the hoses are all, I believe, original so this also seems possible but the mechanic doesn't seem to think so.

Basically I am just really hoping this isn't a head gasket issue... any thoughts? I read somewhere else that it could be a bad radiator cap or something causing the pressure... what are the odds of that? The car doesn't have any obvious signs of a blown head gasket.

Edit: Also, I should point out that while the mechanic said that the system is building up pressure rapidly, the top rad hose gives no sign of being under pressure... I don't know if this is significant at all.

 

First off you can't trust the factory temp gauge.It will not tell you true temps.If you were close to red your engine is getting cooked.Buy a decent scan reader like a ultra gauge. It could be any of those problems but if that mechanic can't test for head gaskets move on to someone else quick.You can buy or rent a coolant test that will let you know if it is the head gaskets.If you are mechanical the others are not too bad to fix.

 

Thanks for your reply! Interestingly, even when the gauge read hot, other than the one time that the heater core hose blew, the car has never steamed or "boiled over" depite getting almost into the red... is that odd?

Is there any rationalizing that this could be something simple as a rad cap or is that just wishful thinking?

 

It could be as easy as a new cap.Depending on miles and upkeep the rad is probably gunked up.Flushing will not help.Will need to be rodded out.Check out the cooling section of the d1 section.

 

1. Ask mechanic if he connected a scanner to read data "live". There is also a chemical test that "smells" the coolant and changes color if exhuast gas is present. Don't want gurggle sounds under dash.

You can test the radiator for clog with an IR thermometer, if lower rows read more than 10F cooler than top rows, then blockage is present.

 

Today I went to autozone and picked up the test for exhaust gases in the coolant. Ran the test for about ten minutes (the instructions only say it needs to be done for 2) and the liquid stayed perfectly blue, indicating that the head gasket is probably not the cause of this issue. Hurray!

I drove the car today for about a half hour and it never got hot (according to the dash gauge) and even pulled my brother-in-law's subaru out of a ditch without any issue.

Here is what I am thinking I should try next:

1. Replace the clutch fan? The clutch fan cannot be spun by hand when the car if off, however it spins with the motor. The mechanic does not seem to think this is the problem, but he is by no means an expert...

2. Put in a 180F thermostat? The thermostat has been replaced twice now, but I would assume that they used the 195F stat. I read about the 180 stat on this forum and am wondering if it might be worthwhile to try that.

3. Replace the overflow cap? This is sort of a shot in the dark, but who knows.

4. Replace or have the radiator rodded out. My mechanic said that he would put a new radiator in for me for free if I bought it (he felt bad about the car not being fully fixed)

What would be the next logical step in terms of diagnosis? Can any of these things be logically ruled out?

 

You can pick up a Ultra gauge for about $75 bucks and find out what the actual temps
are running and go from there.Considering the age all options above probably need to be done.

 

You will not like the price of a new copper radiator. $700ish. $235 for aluminum one.

Fan with engine off - should spin 1/4 turn maybe. Should not spin a whole revolution when hot. But should move some. Or it will roar like an airplane all the time and devour gas. Makes big change at idle of when slow.

180F stat is a plus. Having digital readings of temp so you can tell when to stop throwing parts at it is a plus.

 

The clutch fan will not spin at all by hand, regardless of whether the engine is hot or cold. Could that be causing the overheating issue?

When you say the 180F stat is a plus, do you mean that it is better, but probably won't fix anything or that could it be the source of the problem?

Drove the car around today for about a half hour and it stayed cool the whole time (below half on the gauge) but just as I pulled into my driveway the needle inched up to a little over half... the problem is so sporadic that I think it could be something stupid.

I will try to get my hands on something to check the actual temps as soon as I can.

 

Clutch is frozen. Needs to be replaced. Will increase load on engine (poor mpg) and wear on water pump. If this has been going on for sometime, consider replacing water pump at same time. That said, it would not be source of overheat, as it increases airflow thru the radiator.

180F stat is an improvement of the situation. My D1 with 180K was running up to 221-227 in spikes, even with rad cleaned out by a shop. Put in a 180, it runs 178-183 on back roads and maybe 187 on expressway. In hot, humid, flat land with AC on.

When you slowed down to pull in driveway you have reduced air flow on the radiator.

The $10 thermostat is the cheapest part to throw at it. Also be sure your coolant cap is holding pressure and you are not having coolant loss while driving. If you have gurgle sounds under dash, then bubbles could be keeping thermostat and heat gauge sender from actually touching the hot water. Coolant needs to be full.

If you don't have an OBDII scanner, stop at a parts store for a free code read with one of their's, and while connected let them demo the live data capability. Look for coolant temp.