Greetings gentlemen.
I need some enlightenment as regards the thermostats. I just had my engine done with new bearings all round as the old ones were reading low pressure and indeed had worn out for some reason as was seen when removed.
Crankshaft still std and so are the cylinders hence polished all round and new rings fitted and the heads were also polished, so in all I have a new engine again with only 61K miles.
When I started running in the engine, I was facing overheating issues as the gauge would go to Just above the middle line, 1st photo below, without using the AC. But if I am stuck in traffic, the needle will continue to kreep up and can reach the line before the red mark, at which Time I would stop.
Now if I use the AC, it will get there very quickly, almost as soon as I get into slow traffic. 2nd photo below
I read many posts here about overheating and thermostats that I suspected the thermostats, and when asked my mechanic, he said he installed single units used on Range Rovers as opposed to the ones that also work on the bypass. Sorry not familiar here with the wordings.
I took them out and want to try the car without them to see if that issue goes away before getting correct ones. Photos 3 & 4 below.
1. Are these the culprits indeed? And pls explain why?
2. How do I know that there is a bypass in my cooling system that many have referred to?
The reason I ask the second question is due to one explanation I read somewhere on this forum mentioning "the right thermostat for engines without the bypass". So I need to know what to look for.
Grateful for any guidance.

Thank you

 

Those are definitely incorrect, and will cause your engine to overheat. You need the ones with the bypass cutoff plates on the bottom, and they have to extend the proper distance when hot to shut off the bypass. Your mechanic has no clue what he's talking about.
Download the book at the following link, and read all about thermostats on pages 204 and 205, as numbered at the bottom of each page. Page 205 gives you the dimensions of the bypass closeout you need to have when hot.
http://www.jag-lovers.org/xj-s/book/XJS_help.pdf

 

Also never consider running with no thermostats at all - they are essential to ensure correct flow through the block and heads and although you may think that things have improved you could have created hot spots that the instruments do not see especially at the back of the block / heads.

 

The cooling system works like this:
The correct thermostats when closed allow cold coolant to circulate inside the engine, NOT through the radiator. They are not expensive and look like this:
https://www.ebay.co.uk/itm/224389614...3ABFBMsKiniq5k


The coolant when the thermosats are closed circulates to the water pump via the cross pipe, shown as the blue pipe is this photo:


You can see that this pipe connects the thermostat housings to the water pump

This prevents hotspots in the engine as the coolant heats up and ensures even heating of the coolant. As the coolant heats up the round "feet" on the thermosats, shown in the photo above, start to extend in tandem with the thermostats opening. Thus allowing (a) coolant to circulate to the radiator and (b) the extending "feet" close off the passage in the thermostat housing that allows water into the crosspipe. Thus, when the thermostats are fully open, NO water goes into the crosspipe and it all goes through the radiator.

As your uninformed mechanic has fitted thermostats without this feature, basically quite a lot of coolant, when the engine is hot, is short circuiting the radiator and just recirculating through the engine via the crosspipe without being cooled at all! Hence the overheating.

I very strongly feel that it is important for owners to arm themselves with knowledge of the correct parts and procedures to use before giving the car to a mechanic who is not familiar with them. Then you can explain what needs doing, ensure the right parts are supplied, and ensure the mechanic knows how to fit them. Everyone here will be glad to help!

 

See this photo in the link. This is the distance you need when the thermostat is hot. You can put the thermostat in a pan of boiling water to test, and it must be at least 42mm to be effective. Many are too short.
https://www.jaguarforums.com/forum/x...8/#post2725628

 

Have you checked the temperature with an infrared thermometer? Maybe your gauge and or your sensor are reading incorrectly.

 

Many thanks for your comments and the help book, will read all about it.
Yes I thought as much as I had read about this before and wanted to be sure again.
Cheers

 

For sure will not run without them, but just wanted to test and reconfirm that the thermostats were the culprits.
But as all you gentlemen confirmed this, I will not bother and will just get the correct ones seeing everything is new or as good as new with all whats on the car.

Thx buddy, appreciated

 

[QUOTE=Greg in France;2778419]The cooling system works like this:

Thanks a lot Greg for your detailed response, really appreciated and helps me understand more about my car and also compare things to my engine.
Whilst I understood the concept of the by-pass which I guess is not very common with other classic cars in this manner, I did not know where the actual pipes are.
Now I can see and will compare with my car.
As for the supplier, I read in one post a different supplier indicated by one of the members which is also from UK, but at a much reasonable price, see below.
I guess I will opt for him although these may not be Jaguar Originals but I guess they will do the job. Anyway I cannot buy anything from ebay worldwide as they do not accept any payment from my country Lebanon.
Thank you once again for the enclosed details that are much appreciated.
Cheers

 

Thanks a bunch, yes well noted and appreciated.

Cheers

 

DO NOT RUN WITHOUT STATS, YOU WILL COOK IT IN 10 MINUTES.

Read the sticky at the top of this section "Cooling system maintaining............"

Its all there, and the dozens I have sorted over too many years have NEVER returned with issues,

 

Thank you for sharing your thoughts.
Actually I did as I suspected the gauge or sensor, and what I got at the hottest time that I allowed the engine to got to was 91 C on the electric fan side and I think 96 or 97 C on the other (right) side.
Below are a couple of photos taken when the I saw the gauge rising up but not at the hottest I got to. These reading were taken on the top of the hoses where they enter the radiator.
Incidentally, someone mentioned 94 C as what it should be showing there? Is that correct?
If not what temp should I get on these hoses?

Thanks again for chipping in.
Cheers

 

Worry about the exact temps AFTER you get the correct thermostats installed. It WILL overheat without them.

Jon