2003 S type R overheating in the strangest way
 

Hello all

This is my first Jag and I bought it knowing there were issues. The one that has me stumped is an issue I am having with over heating. The problem is it only over heats after about 10-15 mins of driving. I can have it idle or revving it in the garage for 20 mins straight with no problems. (I did this multiple times) Then take it for a drive and it over heats in about 10 mins or so. The rest of the time it sits dead center of my gauge. Even my odb torque app tells me it sits at 200 until it starts to over heat. These are the steps I have taken.

I first tried to burp the coolant system multiple times. I did get some air out.
Then I changed the thermostat. No change
(other note is that I dont have heat in the air con. I have read about the dccv) Could this be the problem?

I have driven the car 4 times now and it always does the same thing. Works perfect until 10-15 mins in. Like clock work. What am I missing? How is the timing so percise? Thanks
(FYI it doesn't matter if I floor it or drive nice. Always a time thing)

By the way the on the only code I have had is a Bank 1 knock sensor. The car sat for a while so I put some octane boost in and the problem has gone away.

Be aware the dashboard temperature gauge is deliberately misleading, as detailed at the following link, so don't rely on it. This is from the XK forum, but the general principle is the same on the S-Type:

https://www.jaguarforums.com/forum/x...e-gauge-62813/


So for any troubleshooting, make sure to use the OBD data, NOT the dash gauge. Do not overheat the poor engine.

How fast are you going when the engine begins to overheat? On my '02 V6, the electric fan died one day and I was able to nurse the car home by keeping the speed above 30mph as much as possible. Below that, the temp would start to climb. Above that speed, there was enough ram airflow through the radiator and the dead fan didn't matter.

Does the electric fan kick into high speed when the engine runs hot? It makes a lot of noise when this happens, so you should be able to hear it.

Also, the overheat test at idle doesn't help a whole lot. The engine is barely working then, so it doesn't take much effort to cool it.

The lack of heat is an interesting clue. Have you tried raising the desired temperature until HI is displayed? This puts the climate control system in manual and bypasses many of the auto inputs. The coolant flow to the heater on the V8 is marginal at idle speed, so an auxiliary coolant pump is used. Does the heat work at speeds above idle? If so, that would point towards a failed aux coolant pump. Could be the lack of heat is a separate problem, so it may not be related to the overheating.

I have the readings of the temp from an obd app (torque) and I get fluid spewing from the overfill cap. So I know its running hot.

It doesn't matter how fast I go. In fact faster only makes it worse as it heats the engine faster. but it will start overheating whether I am going 60 or 30.

The electric radiator fan kick into high with no problem. When I turn the car off it continues to run to cool the car further.

I have tried driving with the air con on and off. Hot and cold. Hot one side cold the other. Fan manually turned up to high at all temps. Doesn't seem to mater.

I will check to see if I get any heat with some higher RPM's.

further more my obd 2 tells me I'm running around 203 when normal then all the way up to 235-245 when overheating.

If you replaced the thermostat with an aftermarket one, that is most likely the cause of the condition.

Another possibility is a failed water pump having a broken or loose impeller.

As stated in post no. 3, DO NOT rely on the instrument cluster gauge as an indication of the engine temperature as it does not change between 86C and 129C. Head gasket failure or block/head warpage is possible if the engine temperature exceeds 125C.

Uff da! I had forgotten something very important about the S-type cooling system. From my limited experience, the coolant flow on these cars is very temperamental if normal operating pressure can't be reached.

IF (a big if) the only problem is the cap has been relieving pressure too early, the fix is simple. If normal operating pressure can't be reached, that would explain the high temperature, spewage from the cap, and lack of heat.

The scary thought is a combustion leak into the cooling system, and the cap itself is fine and venting at the normal limit as designed. To check, pressurize the system with a cooling system pressure tester. See if the system can hold pressure. Test when the cap vents. There are also special testers that show the presence of combustion gasses in the cooling system.

If you don't have a pressure test set, I'd be tempted to just try a new cap first and see what happens.

check radiator in multiple spots with an infrared thermometer.
possible clogged rad.

The cap doesn't loose fluid until the needle is just before the red. In my opinion it is working properly. Not trying to shoot down idea as I appreciate all of them. Maybe I'll go grab another one just to try.
I am also going to see if I can rent a pressure checker from our local auto parts store.

I have thought about the head gasket as well but I ran a test in the garage revving the car between 2500 and 4000 rpm for over 15 mins and not a single change in coolant temp. The fan kicked on as normal and everything. I would think if it was a head gasket A. I would see more crap in the coolant B. it would have failed that test I did.

Is there any electrical pumps in the system. Could I have a bad relay or something?

As far as the thermostat I have two of them. They both pass my boiling water test and my test drives were so identical with both in use. I feel like that should rule that out. But I'm not apposed to buying a new one just to make sure.

Purchase a Jaguar OEM thermostat. The part number, depending on you VIN is AJ811788.

Do you see coolant moving through the expansion tank at all?

Ooh, the needle approaching red makes me cringe. I'd strongly suggest avoiding letting the poor engine get anywhere near that hot.

Also, the spewage/high temp may be a chicken/egg kind of thing. In other words: Which came first? If the cap is good and the fault is elsewhere, the cap is acting as designed to vent excess pressure due to high temperature. However, if the cap (or mating surface on the reservoir) doesn't seal properly, normal pressure can't build up and the cooling system misbehaves. As previously mentioned, you've got to have normal pressure or the coolant doesn't seem to circulate properly. So in a situation like that, the cap itself is the problem, both for the spewage and the high temperature.



I've never heard of this test. I'm not sure it's telling us much of anything.

And an unloaded engine screaming at 4000 rpm? Ooh, that's REALLY tough on the connecting rods. Strange as it seems, it's actually easier on an engine to work hard at high RPM versus unloaded. When the engine is loaded, you've got higher combustion pressure pushing down on the pistons, and that helps take up any slack at the wrist pins. Do the same thing unloaded, and the pistons tend to float up at the top of their travel and hammer the wrist pins. I'm surprised you were able to rev the engine that high. I thought these engines have an RPM limiter when in park.

One electric pump, auxiliary only. It's to boost coolant flow to the heater at low RPM. It also runs for a little bit after shutdown if the engine is above a certain temperature. If failed, you'd probably never notice, other than poor heat at idle.


Are you measuring the water temperature, or just letting it boil? A 190F thermostat, for example, should open at least 20 degrees before the water boils on your stove.

Another thought: Any chance your thermostat was installed backwards? It doesn't matter how many you try if they keep going in backwards. Don't fall into the trap of "I've changed this part x number of times so it must be something else..."

Well I was able to get back at it yesterday and I decided to eliminate the possibility that it could be the thermostat. So i took it out completely. And this time I watched the temps more closely on my torque app. As said once before do not trust your gauge at all. I watched my temps go up to 225 before the gauge even moved. So I think this is going to explain my gauge jumping up after 10 mins. It was just stuck.

Now the bad news for me is that even with the thermostat pulled it was still over heating. I know the water pump is working as it can pump out water from one of the top hoses with good flow. My next step is going to be to test the pressure of my coolant system. I have a feeling that I may be looking at a head gasket :( I will also get a test kit to test the coolant and see if that blue dye changes color or however that kit works. I'll keep you guys updated. Thanks for all the ideas and help.

It may be time to break out the forum's tranquilizer dart gun. You'll only feel a slight tingling sensation, followed by restful bliss in which you take no further counterproductive action. It will be a lot easier for everybody.

All seriousness aside, the S-type thermostat is different than most vehicles. You're probably accustomed to the older variety, where the thermostat is a simple on/off device in a basic loop. If stuck closed, the engine will run cooler without the thermostat.

The S-type thermostat is more of an either/or device in a series of Byzantine passages. the thermostat routes hot coolant either to the radiator or to a bypass hose. Remove the thermostat and the bulk of hot coolant will bypass the radiator. Your engine should overheat with the thermostat removed. If it didnt, something is really wrong.

Well that's good to know.

I guess ill have to look up the flow of the thermostat and see if it was in backwards or something. And I will buy a NEW one just to make sure.

Thanks

There is also an auxiliary heat pump (not the engine water pump) in an obscure location that could be the cause. I had a very similar issue and pump replacement fixed it.

Rex,

I'm confused about the aux pump. Was your car having an overheating problem, or was it just low output from the heater?

Details of the aux pump operation here, on pages 3.3.2 to 3.3.4:

http://www.jagrepair.com/images/Trai...des/703_SG.pdf


An excerpt showing when the pump operates:


https://cimg7.ibsrv.net/gimg/www.jag...e9510ba337.jpg

It was overheating. Changed thermostat, bled system etc. Replaced aux pump and all fixed.

Well last night I tried to put the thermostat back in and 2 of the three mounting holes stripped right out. I pulled the whole thing and I am going to tap it to the next size up. While I have everything accesable I am going to pull the aux pump and the dual climate control valves and test both. More to come.

Um, I'd highly suggest NOT making more work for yourself. For example, the thermostat replacement didn't go so well. You don't need to break off any more bolts, etc.

Don't just tear apart stuff in hopes of a random fix. Run some basic troubleshooting first. Beg, borrow, or steal a pressure tester, as previously suggested. Specifically, pressure test the cap, too. Get some of that stuff that lets you test for combustion byproducts in the coolant, too. Nothing has to be disassembled for any of those tests.

I will try to test them without taking the parts out. Hopefully I can unplug the wires and test while in the car.