Magic MPG, and head questions.

I over heated the crap out of my 2001 XJ. Realy bad. The valve cover was smoking after I shut it off and opened the hood. So I towed it home. Poured the bone dry radiator full of fluids. I put in a 195F thermostat from NAPA in, and I noticed it did not have the little bleed ball thing on it. It had no hole so I put it in like it was with a new gasket. After that I had a flush done. Well I fill up the tank and start driving around. WOW!!! Gas milage is amazing!! If I filled it, 1 tick mark on the fuel gauge would get me 23-25 miles tops in town! Now I am getting about 40 miles per mark. Must have been the thermostat?? Also The temp is about one to one and a half tick marks below 210 now. It use to always be at 210.

I know the 2001 "0331" heads are known to crack. But I dont think mine did? I can not see one threw the oil filler. I been told to check my coolant like a hawk. Is it the coolant bottle I need to watch?? Cause since the flush and all and after 40 miles the bottle has only filled up just a bit from were I marked it when it was filled and flushed. So no coolant use? My oil looks perfect and when it is cold outside my exgaust barely steams at all, were every other car does. So I am guessing no coolant is being burned or lost???

Should I feel at ease?? My valve cover did have a tick from the side closest to the firewall but it went away after the second warn up. My oil pressure also been normal, but my oil change is due.

Just monitor things for now, but you do need to ask yourself where all that coolant went to cause the overheat?

joe_peters said:

Just monitor things for now, but you do need to ask yourself where all that coolant went to cause the overheat?

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I never checked the levels and the coolant looked like apple cider. Pure rust and flakes. I lost all the coolant or whats left due to over heating I guess. It steamed forever. But good good point

Makes me think I should try replacing my thermostat. My mileage has to be at around 10 to 12 MPG. I'll have to pay closer attention to my temp gauge. I thought it was running at normal temp, but maybe not. Might solve my heat issue too, being that's what another thread was just talking about, which someone also mentioned improved mileage off of a new thermostat. Guess it couldn't hurt, I'm sure they can't cost much more then 15 bucks if that.

CodyJames, what's the oil pressure reading on your XJ, at idle and at cruising speeds? My 2000 XJ overheated last winter when the water pump went out.

el_roy1985 said:

Makes me think I should try replacing my thermostat. My mileage has to be at around 10 to 12 MPG. I'll have to pay closer attention to my temp gauge. I thought it was running at normal temp, but maybe not. Might solve my heat issue too, being that's what another thread was just talking about, which someone also mentioned improved mileage off of a new thermostat. Guess it couldn't hurt, I'm sure they can't cost much more then 15 bucks if that.

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Mine was 6.50 with gasket at NAPA

dieselenthusiast said:

CodyJames, what's the oil pressure reading on your XJ, at idle and at cruising speeds? My 2000 XJ overheated last winter when the water pump went out.

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I think about 30-35 but I will have to check again

I know it is 45psi at 55 mph

It is possible that you got lucky with the overheat on your 01. It is also possible that if the head was damaged, the results of that crack haven't surfaced yet.

As you know, you need to WATCH THAT COOLANT LEVEL extremely close. If I were you, I'd be checking it every day for quite a while to build up confidence.

Of course, the level in the reservoir moves up and down between the min/max lines when cold and hot.

So know where it runs at COLD. Before you start your engine, check to see if it is at that baseline level. If you see that level changing when you check it, you may have problems.

The #1 symptom of a cracked 0331 head is coolant loss.

I own a 2001 xj, also was loosing coolant at a slow rate. For 2 years could not trace it, but always would smell antifreeze. Check oil for coolant none in there, no crack in head. No signs of a leak anywhere. Last december I finally found it. It ended up being a small leak on drverside of the rad. So i did a total cooling system swap at 144,000 miles. New rad, t-stat, water pump, hoses, serp.belt, heater core (evaporator while it was apart/ bad anyway) and coolant. One year later no coolant lose, runs at the usual temp range (200-210). This was what my experience was, you got to look closely to find those small leaks.

Watch for steady coolant loss as well as mayonnaise on the inside of the oil filler cap. I have those symptoms, but nothing shows up in the oil. I am sure the head is cracked. Just coolant loss could be a lot of places, but not the mayo on the fill cap.

jeeperz said:

I own a 2001 xj, also was loosing coolant at a slow rate. For 2 years could not trace it, but always would smell antifreeze. Check oil for coolant none in there, no crack in head. No signs of a leak anywhere. Last december I finally found it. It ended up being a small leak on drverside of the rad. So i did a total cooling system swap at 144,000 miles. New rad, t-stat, water pump, hoses, serp.belt, heater core (evaporator while it was apart/ bad anyway) and coolant. One year later no coolant lose, runs at the usual temp range (200-210). This was what my experience was, you got to look closely to find those small leaks.

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Mine does not leak but I always smell coolant to. How much am I looking at for a cooling system rebuild?

I spent in ballpark figure around $650. Now i did all the work myself, including the heater core and evap. for the A/C.

winterbeater said:

Watch for steady coolant loss as well as mayonnaise on the inside of the oil filler cap. I have those symptoms, but nothing shows up in the oil. I am sure the head is cracked. Just coolant loss could be a lot of places, but not the mayo on the fill cap.

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I had a similar issue recently w/ my '00 XJ. I popped the oil cap and the underside looked a bit milky. I flushed my cooling system and did an oil change, and everything is fine. When the weather gets cold like it is here, and humid, condensation will gather in that spot...especially on short trips. Take any other vehicle, fire it up, drive it till it gets warm, go about 5-8 miles, shut it off, then check the cap...I bet on most vehicles it'll be slightly milky looking.