E21 running a little too hot

**e21Luis** · 09-12-2018, 02:46 PM

So I've had this problem basically all of summer... at freeway speeds above 55mph the car runs at 3/4 temp or past it. All though if it hits that then I run into stop n go traffic it'll slowly go down to 1/2. Even more so with the AC.

So here's what I have

For sure no head gasket problems (no loss of power, mixing coolant/oil)

It has the fan clutch & thermostat deleted

New radiator, coolant and a coolant flush, new hoses, new rad cap

Water pump flows good when I take off the rad cap

I'm pretty sure I bled the system correctly i even jacked the car while doing so.

My efan kicks in with ac or if car gets too hot.

My gauge does jump a little bit with extra load although I got a laser thermometer and it seems that the gauge is accurate. I know I want to much from Stock cooling parts and ac lol but idk what's normal running temp in 80 degree weather. The car runs fine and the only other thing is because maybe I'm running a .32 gap on my plugs and maybe that's too small for this car? I have pertronix electronic ignition so maybe I can try bigger?

**epmedia** · 09-13-2018, 02:17 AM

You may want to try replacing the thermostat in case it's not able to fully open.

Make sure the belt is good and properly tensioned too.

**320iAman** · 09-13-2018, 10:27 AM

Instead of 50/50 coolant try 75 /25, also there is 71C ,75C and 80C Thermostat, 71C open the soonest, there are aluminum radiators out there also with larger core tubes. If you wanted to maximize the cooling from the coolant perspective-use 100 % distilled with water wetter or similar and water pump lubricant with anti rust-this also lubricates the thermostat as well, so long as your not in area where the temperature goes down too far where you need anti freeze properties of coolant, near 32F and below. I have run 100% distilled water + a water wetter--this is the coolest it will get on hot days.

Fan Clutch ? I never seen one of those on these cars. No thermostat ?

With the auxiliary fan installed, the air flow thru the radiator will not be maximized, maybe you should go with an electric puller fan system with thermocouple.

Randy

**e21Luis** · 09-13-2018, 11:58 PM

So I tightened the belts but they weren't too loose to begin with. The thermostat is deleted so that shouldn't be a problem. I drove the car till it got to 3/4 on the freeway and checked hoses for bending while giving it throttle but everything was good. I'm pretty bamboozled

**epmedia** · 09-14-2018, 11:56 AM

Why was the t-stat removed? It does not help anything to remove it, far as I'm aware

Also, is the heater control valve, by chance, bypassed with a piece of hose?

Or maybe that hose junction? block that bolts to the cyl head is clogged a bit?

**e21Luis** · 09-14-2018, 11:34 PM

Actually I bought the car without it and I live in Los Angeles so It never really gets too cold. But the heater is connected to the block by the distributor and since it has a 76 manifold for a carb it goes to the intake and then to the water pump on the other side of the manifold.
I added water wetter today but it didnt really help.

**epmedia** · 09-15-2018, 05:42 AM

Originally Posted by e21Luis

Actually I bought the car without it and I live in Los Angeles so It never really gets too cold. But the heater is connected to the block by the distributor and since it has a 76 manifold for a carb it goes to the intake and then to the water pump on the other side of the manifold.
I added water wetter today but it didnt really help.

I'm going to assume you have a pre '80 e21 (because petronix)...

I cannot visualize your engine cooling system/heater setup, so I'll just mention some tid-bits for now:

The heater hose should be **restricted if the heater matrix or heater control valve is not being used, because there will be reduced coolant flow through the engine radiator. Visualize this:: coolant flowing through the heater hose(s) is expecting to get cooled by the heater matrix(heater radiator) before it makes it's way back into the engine. Also:: coolant that flows through the heater hose(s) never reaches the engine radiator! - it just cycles in and out of the engine. Expect maybe 10-20% loss of cooling ability if this scenario fits.

**not completely restricted, maybe just down to a 1/4" orifice (hole).

I forget exactly how our thermostats operate, maybe one hose gets closed as two others open more. Wish I knew! If that's the case, this could lead to significant loss of cooling ability. Was the t-stat gutted, or removed completely?

Can you post pics of the heater hoses routing and hoses where the t-stat is suppose to be?

**e21Luis** · 09-15-2018, 03:14 PM

20180915_115213.jpg 20180915_115134.jpg 15370385574306811601983329652119.jpg

- - - Updated - - -

So first pic shows the top hose that goes from heater to the manifold the bottom hose goes from the head to the heater

The second pic shows the hose that goes from the intake to the water pump

And the tstat was gutted I do hear some bearing noise mainly on morning startup and I took of the fan belt and my wp bearing felt good but the alt was a little squeaky but didnt feel totally worn or dry. Again both belts are tightened correctly so I doubt its belt noise

**epmedia** · 09-15-2018, 04:20 PM

Thanks for posting those pics. At first I wasn't sure about how the heater hoses were arranged - looks good.

I think what I would do is install a new thermostat. I'm pretty sure that while it's gutted, the coolant may not be flowing properly, ie: a large portion of coolant may not be flowing through the radiator. I wish I had a t-stat to look at it's guts, but no sense in trying to guess what's actually happening inside the t-stat - just make it proper with a new t-stat and fingers crossed that it helps!

**gsumzzz** · 09-16-2018, 07:19 AM

oem fan and shroud will do it. tried electric myself with your results. really.

**e21Luis** · 09-16-2018, 12:59 PM

Ahhhh btw I just noticed the coolant neck coming off the intake side of the engine on my e21 doesn't have the 3rd outlet for the hose coming off the intake near the vacuum advance. Its blocked off on my intake would that effect the cooling at highway speeds?

**GDAus** · 09-18-2018, 12:13 AM

Originally Posted by epmedia

Thanks for posting those pics. At first I wasn't sure about how the heater hoses were arranged - looks good.

I think what I would do is install a new thermostat. I'm pretty sure that while it's gutted, the coolant may not be flowing properly, ie: a large portion of coolant may not be flowing through the radiator. I wish I had a t-stat to look at it's guts, but no sense in trying to guess what's actually happening inside the t-stat - just make it proper with a new t-stat and fingers crossed that it helps!

Yep .. agree with Robert (Epmedia) on this ... extremely bad idea to gut your thermostat because you are now allowing a lot of water to take a shortcut back down to the water pump without going through the radiator.

The thermostat on the M10 is a bit more complicated than usual. In a "normal" thermostat there is only 1 valve .. when it is shut it prevents water flowing into the radiator and there is a smaller, constricted passageway to divert water back to the water pump, allowing the water to circulate around the block. Which allows the engine to heat up quickly (reducing engine wear and fuel wastage). Once the thermostat starts to open ... the water takes the easier path through the radiator and then back to the water pump. In theory, in a well designed cooling system, the thermostat shouldn't be open fully under normal conditions, so it can open or close to regulate the engine temperature depending on conditions. Of course the M10's system seems more designed for cold Bavarian winters, than hot Australian summers.

Anyway .. the M10 thermostat has 2 interlinked valves ... 1 to shut off the bypass from the top of the cylinder head and the 2nd is the conventional regulating valve.
Basically with no internals in the thermostat housing ....there is nothing to stop a lot of hot water bypassing the radiator and simply being recirculated straight back into the water pump and engine. The field sketch I've drawn should make it easier to understand.

One other thing ... I'm not sure if this applies to the M10 engine .. but with engines with conventional thermostats, the thermostat usually also acts as a deliberate flow restrictor to ensure the coolant circulates properly around the rear most cylinders as well. I've rebuilt a couple of other peoples engines at different times that made that mistake ... having your engine start spitting out bits of it's rear piston(s) through the exhaust is usually embarrassing and expensive