My 2006 Super V8 with 133K miles has run at about 200 F in coolant temperature for the 7K miles we’ve driven it, but one dark evening this week my wife called and said it had overheated; She thought she had driven about three miles from her church when the temperature gage needle rose to the top and the red light above it came on so she pulled over. I had checked the coolant a week ago just before my wife took a trip and had topped up the Dex-cool to the max mark. I took the Land Rover to pick her and her lady friend up and one of her church friends who had stopped said he thought the top radiator hose was leaking because there was coolant on the engine cover. I started to open the coolant tank cap but coolant bubbled out so I retightened it. Starting the engine to move to a safer place to leave it overnight, the UltraGage showed 140 F for coolant temp.

Next day I loaded up tools and drove back expecting to find a bad hose, but the hoses I could see and the serpentine belt all looked OK. There were no engine codes set nor any Jaguar specific codes related to cooling. The coolant level cold was above the max mark in the expansion tank and when I had my wife start the engine with the cap off there did not seem to be any flow in the tank, but there was a bubble or two that came up as it idled. I decided to try driving toward home and monitoring the coolant temp on the UltraGage; it held steady at 95F for a mile or more and then began to rise until the temp gage needle was near the top, the red light came on, and the UG showed 246 F (The UG has a range of -40 F to 420 F). It continued to hold at 246 F for several miles until I found a safe place to pull over about 7 miles from where I started. I let it idle just a minute, turned the engine off, and opened the bonnet. There was coolant on the engine cover and around the reservoir cap and the electric fan ran for a minute or three and then shut off. I decided not to chance driving further, went home to get my tow car and trailer, and hauled it home. At home the next day both the coolant in the reservior and the oil on the dip stick looked normal and the coolant level cold was below the MIN step in the reservoir.

I assume that the temperature holding at 95F for awhile and then rising steadily indicated that the thermostat had opened? And perhaps that holding steady at 246 F indicates the pressure starts to blow off through the reservoir cap?

So…should I be looking at a new water pump? Any other possible causes of overheating that do not include oil in the coolant or coolant in the oil? My wife did say that a week ago while on her trip that when she used the windscreen washers steam came up from under the bonnet; Could it be related somehow? (of course she thinks so). The driveway in our car port has about a 4 degree slope nose down; I’ve been parking there for nearly a year with no previous ill effects. Could that slope cause air to accumulate in the cooling system? All suggestions will be appreciated.

 

The easiest way to get your answers Phil is with a IR thermometer. Once you get her home, firs it up and as it warms up, check temps on either side of the thermoses to determine what temp it opens, if it opens.

You can do the same with the water pump as the temp should be consistent on the outlet as it is with the inlet.

Start there and let us know.


Longer term, you shouldn't ever have to top off your radiator. You have a leak and should fix it, but it doesn't appear to be your current issue.

 

My 05 Super V/8 sprayed coolant onto the engine cover as well. Pressure tested the system and found a small hose under the upper radiator hose had split. It runs over to the right and down to a metal line which I believe is a heater hose/ pipe combination. I replaced that small hose and upper hose as insurance and replaced the original 10 year old radiator cap. Parking down hill has no relation to air in the system. If you had air, the temp gauge would not have registered hot. For a gauge to move, it must have coolant surrounding the sender in the system. Pressure test it at 15/16 PSI and I think you'll find your leak.

 

Thanks guys,

I'll see if I can rig up a pressure test and check for leaks tomorrow. I have to study up to see exactly where the thermostat is, and I do have an IR thermometer.

Today was a "start slow and taper off" day after spending yesterday in the heat loading the SV8 and then having the oil light come on in my tow Jeep and its oil cap twist off when I tried to remove it to add a quart of oil; I had to rig a funnel from cardboard and drizzle a quart of oil down the dip stick tube for the drive home. I'll have to deal with the Jeep's oil cap later.

 

Cheap and easy first thing to do is check/replace the thermostat. No coolant loss indicates no leaks. Water pumps were troublesome on early V8s, but the 4.2s were OK AFAIK.

 

I had overheating issues last summer that I just couldn't figure out. No leaks, everything was functioning perfectly...except for the fan. Sometimes it would work, sometimes it wouldn't. I finally realized it when I had the AC on and it wasn't blowing cold. The fan should also turn on with the AC, and mine wasn't doing so half of the time. I replaced the fan and the coolant temp sensor and everything has been fine since.

 

Good call. I pulled the T-stat housing, added a wire twistie aligned with the top hat and put it in a pan of water on the stove with a candy thermometer and up to a boiling 212 F the top hat never moved, although the inside rubber edged disk did open a little - maybe 1/8".

I can't find a description of how this T-stat is supposed to work; Are both ends supposed to retract?

The spec in the manual says "On the 4.2L supercharged engine the thermostat begins to open at 84°C (183°F) and is fully open at 98°C (208°F)", so I am guessing this one must have failed if is is supposed to uncover the seat in the housing to the hose and the seat in the block at the same time.

What is a good source for a new one? Local parts house web sites show a more normal T-stat and not this one, and ebay shows a whole raft of the wrong ones saying they fit my car. I checked merriam and theirs is $45 including the seal. Sound about right? At least from them it should be the right thing.

 

I've given this some more thought and I am sure the coolant on my engine cover came from the pressure cap. I intended to do a pressure test of the system with my bicycle pump that has a gage on it, but I decided to test the thermostat first and am now awaiting a replacement before I can do a pressure test.

Fingers crossed that the T-stat is indeed the cause and once replaced and the system purged we will be back in business and I can continue persuing the front end klunk that I suspect from other threads here could be the Arnott air shocks. I'll report back after the new T-stat is in.

 

If a car is overheating, eventually, the pressure is sufficient to blow-off the pressure cap, as it is designed to do, i.e allow a certain pressure to build up, thus stopping boiling, but eventually to blow off and prevent damage elsewhere.

 

The thermostat and seal arrived from Merriam at noon yesterday and I got it installed in the housing by stacking the components with the top hat against a block on the floor pressing down against the very heavy big spring and turning it so the bracket ends located in the tab slots on the housing; took several tries. I tested it in a pan of water on the stove and the top hat still does not move (guess it isn’t supposed to) and the rubber edged disk did appear to open a little farther at 212 F than the old one but not much. I reinstalled the T-stat housing in the SV8 and I started to remove the bleed screw from the reservoir but coolant bubbled out so I re-tightened it (barely hand tight - spec says 1 Nm which is 9 inch pounds), topped up the reservoir to the max step (which took half a gallon or more), and went inside to escape the mosquitos.


This mornning I removed the reservoir pressure cap and bleed screw (coolant did not come out of bleed screw this time) and the level in the reservoir went down. I refilled the reservoir to the max step and coolant appeared in the bottom of the bleed screw hole. I reinstalled the bleed screw and the pressure cap and made up a pressure testing device with a Schrader valve stem on a Ľ” T and installed it between the vent hose and the vent nipple just below the bleed screw on the coolant tank. I used a bicycle pump to pressurize the system intending to do it at 14 PSI, but I hit just under 20 PSI or 1.1 bar on the bicycle pump gage. I left it for an hour and the pressure did not go down until I loosened the pressure cap and coolant bubbled out around it and was then above the max step in the reservoir. When I removed the T, the coolant level in the tank dropped again, so after I reinstalled the vent hose I removed the bleed screw, topped up the coolant to the max step again, and reinstalled the bleed screw and pressure cap.


Now I have another question. The 4.2 with supercharger fill and purge procedure says to remove the supercharger fill plug and top up the coolant there, but also says to use a new sealing washer which I don't have and which Merriam apparently doesn't stock, so I am wondering what are the chances of getting a bad seal if I try to re-use the old one. Further, how important is it to do this step if I have not drained the system? I'd hate to be stuck with a leaky fill plug and no way to correct it. I am thinking i'll just do the "run the engine and turn the heater to max" steps to see if the overheat condition is gone, but my **** side says I should do all the steps in order. Will the Supercharger cooling system purge itself through the main reservoir, or must I do the SC "filler plug removal - ignition on" steps?

 

I used my original washer on the SC plug with no problem whatsoever. I have taken it off several times when I was swapping out my super charger.

Also very quick and easy to "purge" the SC coolant system with just the ignition on without engine running. I topped up the reservoir and only topped up at the plug for the very last step.

 

Just raise the front wheels (car ramps are perfect)
Turn on the Ign but dont start
This runs the aux and SC pumps which will bleed out all the air in a few minutes
Top up as needed

Raising the car makes the reservoir cap the highest point rather than the IC plug
The 2 pumps will circulate coolant and remove the air for you

Cheers
34by151

 

Put it back on the highway to see if this has cured the problem.

 

+1 to 34by151's comments. That's all you need to do to bleed the air. Before you run her up the highway, let it idle to full operating temperature in your driveway and put an IR thermometer on it. Once the thermostat opens, you get the same reading on both sides. You'll be assured the the thermostat is open and then you can take her for a spin, minimizing your risk of overheating again.

 

Thanks, That gave me the courage to try, but I need to make a tool to remove the plug. I tried a 1/2" bolt with a 3/4' hex head with two nuts jammed on it, but the plug was too tight and the nuts turned - I'll have to weld the nuts on and try again.

 

Thanks, Since I didn't get the plug loose first try, I'll try the nose up warm up instead. I was hoping the SC cooling was designed to purge itself via the reservoir. Fingers crossed as I get out the ramps.

 

Thats exactly what I did. My plug was very tight but did move.

Going up on ramps will work obviously but a lot less of a hassle if you can remove the plug.

 

Ok, I put it nose up and let it idle for half an hour with the climate control set on high (hard to get it to blow hot air in 98 degree ambient) and the hottest it got on the UltraGage was 197.6 F with 190 F on the top radiator hose. So Far So Good. Tomorrow when it is cooler I'll recheck the coolant level and take it for a test drive. Fingers crossed because Momma wants to take a trip this week end.

 

The coolant level was Ok this morning so I took a 15 mile drive to get sunflower seeds for the birds and the temperature held right around 200 F as normal and the needle stayed right in the middle of the dash gage. Eureka! Momma is happy again so I am too.

 

I like happy endings!