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Tue Jul 08, 2025 12:16 pm

I have a 74 bus that i rehabilitated over the last few years. The engine is mostly stock 1800 rebuilt by painters grinding in Denver. I installed it with new Weber ICT’s with CB performance linkage. I have a wideband gauge / o2 sensor that helped me get the carbs dialed. It’s set at about 12 w.o.t., 13.5 at idle. I installed a rebuilt Bosch svda distributor and it’s set at 32 btdc vaccuum line plugged (painters told me to set it there). The cylinder temp is monitored under cylinder 3 plug and is typically under 300, but will climb as high as 330 when climbing long hills in the summer.

My oil temp is the issue. Using only the oem oil cooler, the oil temp quickly goes up to 250 and even 260 before I would pull over. I installed a remote oil cooler and it runs no hotter than 230 on a 100degree day. So problem solved. But I kind of hate having the remote oil cooler. I don’t think it should need it and there’s all these extra parts that can fail. I think there’s an issue with the oil cooler bypass valve. What do you guys think? Is there a way to fix this valve if it needs fixing? It seems like there’s issues with a gouge and some metal ridges where the valve piston should meet the case. I tried to add some pictures.

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Tue Jul 08, 2025 1:55 pm

I have messed with these on type 1s in the past and found some that were stuck in there. My solution was to get it out, clean the piston and spring and then with wet type fine sandpaper and oil and a dowel work the passage until the piston moves freely in there. A lot of do a little and try it type thing. When you are satisfied with the fit flush it out with wd40 and put it back together. Good luck-Bob

Tue Jul 08, 2025 2:52 pm

Bobs67vwagen wrote: I have messed with these on type 1s in the past and found some that were stuck in there. My solution was to get it out, clean the piston and spring and then with wet type fine sandpaper and oil and a dowel work the passage until the piston moves freely in there. A lot of do a little and try it type thing. When you are satisfied with the fit flush it out with wd40 and put it back together. Good luck-Bob

That makes sense, thanks. The piston was kinda stuck in there.

Tue Jul 08, 2025 4:08 pm

I didn't know the grooved plungers were ever used on Type 4 motors.

Thu Jul 10, 2025 6:59 am

KTPhil wrote: I didn't know the grooved plungers were ever used on Type 4 motors.

I have to l99k at the book but I also do not remember the grooved plunger on type 4.

Also, what oil are you using?

Ray

Thu Jul 10, 2025 7:21 am

raygreenwood wrote: KTPhil wrote: I didn't know the grooved plungers were ever used on Type 4 motors.

I have to l99k at the book but I also do not remember the grooved plunger on type 4.

Also, what oil are you using?

Ray

I am currently using Mobil 1 20/50, but I tried 10/40 and it seemed the same in terms of oil temps and pressure.

Thu Jul 10, 2025 9:44 am

captainstick wrote: raygreenwood wrote: KTPhil wrote: I didn't know the grooved plungers were ever used on Type 4 motors.

I have to l99k at the book but I also do not remember the grooved plunger on type 4.

Also, what oil are you using?

Ray

I am currently using Mobil 1 20/50, but I tried 10/40 and it seemed the same in terms of oil temps and pressure.

Ok...if it runs no different with 10/40....then there is no reason for the 20/50 which is what usually causes oil cooler bypass. But before getting into any changes right now, connect q mechanical oil pressure gauge at the port where the oil pressure switch goes and let's see what you have cold and fully warmed up.

Ray

Thu Jul 10, 2025 9:55 am

raygreenwood wrote: captainstick wrote: raygreenwood wrote: KTPhil wrote: I didn't know the grooved plungers were ever used on Type 4 motors.

I have to l99k at the book but I also do not remember the grooved plunger on type 4.

Also, what oil are you using?

Ray

I am currently using Mobil 1 20/50, but I tried 10/40 and it seemed the same in terms of oil temps and pressure.

Ok...if it runs no different with 10/40....then there is no reason for the 20/50 which is what usually causes oil cooler bypass. But before getting into any changes right now, connect q mechanical oil pressure gauge at the port where the oil pressure switch goes and let's see what you have cold and fully warmed up.

Ray

Unfortunately, I don't have a mechanical oil pressure gauge. I do have a vdo gauge using the dual sender at the oem port on the top of the case, and it's reading like 40-50 psi cold at idle, and drops to about 10psi when hot. At 4000 rpm when it's warmed up, it's at about 40psi when using the remote oil cooler. If I'm not using the remote oil cooler, it will drop low enough at idle for the idiot light to turn on when it's very hot. And it's only about 20psi at 4000 rpm.

Thu Jul 10, 2025 11:25 am

Quote: Unfortunately, I don't have a mechanical oil pressure gauge. I do have a vdo gauge using the dual sender at the oem port on the top of the case, and it's reading like 40-50 psi cold at idle, and drops to about 10psi when hot.

This alone looks like you are bypassing the cooler due to excess pressure.

How is this external oil cooler plumbed into the system?

Ray

Thu Jul 10, 2025 11:57 am

raygreenwood wrote: Quote: Unfortunately, I don't have a mechanical oil pressure gauge. I do have a vdo gauge using the dual sender at the oem port on the top of the case, and it's reading like 40-50 psi cold at idle, and drops to about 10psi when hot.

This alone looks like you are bypassing the cooler due to excess pressure.

How is this external oil cooler plumbed into the system?

Ray

I used an EMPI oil filter sandwich adapter (with the thermal bypass valve) and another amazon adapter to get the empi adapter low enough to have the output hoses clear of the push rod tubes. The hoses from the adapter to the cooler are 10AN. The external oil cooler is mounted under the bus frame about 3 feet forward of the engine tilted a bit to catch more air. For what it's worth, the oil pressure readings are about the same when I disconnect the external cooler (by removing the sandwich adapter).

Thu Jul 10, 2025 1:10 pm

it the thermostat controlled flaps hooked up and working correctly, and directing air thru the cooler,is the cooler free of dirt and debris.

Thu Jul 10, 2025 1:21 pm

lil-jinx wrote: it the thermostat controlled flaps hooked up and working correctly, and directing air thru the cooler,is the cooler free of dirt and debris.

The thermostat is long gone, but I have the cooler control flap (took me a few months to round one up) and screwed it down to the square tin air duct thing so it's always forcing air into the cooler. I even replaced the cooler with a new one, so it's definitely not blocked. If I turn on my windshield defrost, there is air moving so I'm sure the fan is moving air.

My best guess is something is not sealing properly with the cooler bypass valve. Like I showed in that picture I posted with my post it looks messy inside the case at the top of where that plunger closes the opening. I'm thinking about getting a milling bit and trying to clean it up. I'm just worried I'll make it worse or ruin the case somehow. The threads for the nut that seal up this contraption are already sketchy. It's a bit of a maze trying to get that back on without stripping it worse than it already is. That's also another clue that some previous owner was messing with this thing trying to get it to work at some point. I should probably just use the external cooler and be happy it works at all.

Thu Jul 10, 2025 3:15 pm

if that bypass valve was stuck ,it would need to be stuck in the opened position in order to bypass the cooler,when oil is cold and thick it takes more pressure to force it thru the cooler,so when that happens the pressure opens the bypass and allow the oil to travel tru the engine ,lubicating it.as the oil heats and thins then it will pass thru the cooler,the pressure it takes to force cold thick oil thru the cooler is greater then the force to open the bypass valve,
so with that i would say the spring in the bypass is so weak that the valve is allways open ,hence bypassing the cooler,or there is a restriction in the cooler keeping the resistance high enough to keep the bypass open.
maybe the rings for the cooler mount are crushed causing the restriction or something got into the cooler,or maybe the temp sender is partly blocking the oil gallery,not sure if that's even possible.

Thu Jul 10, 2025 3:41 pm

lil-jinx wrote: if that bypass valve was stuck ,it would need to be stuck in the opened position in order to bypass the cooler,when oil is cold and thick it takes more pressure to force it thru the cooler,so when that happens the pressure opens the bypass and allow the oil to travel tru the engine ,lubicating it.as the oil heats and thins then it will pass thru the cooler,the pressure it takes to force cold thick oil thru the cooler is greater then the force to open the bypass valve,
so with that i would say the spring in the bypass is so weak that the valve is allways open ,hence bypassing the cooler,or there is a restriction in the cooler keeping the resistance high enough to keep the bypass open.
maybe the rings for the cooler mount are crushed causing the restriction or something got into the cooler,or maybe the temp sender is partly blocking the oil gallery,not sure if that's even possible.

I installed the new oil cooler a few weeks ago and didn't use much pressure. I think there might even be a small leak because I was worried about crushing those seals. I blew easily through one hole in the cooler and it came out the other, so I don't think the new cooler was clogged. My temp sender is installed in the taco plate (I used a Porsche taco plate/sender), so it's at the bottom of the sump. I think the valve plunger/piston is open all the time because there is a ridge of aluminum keeping it open in the case. You can kind of see it in the picture, although it's hard to take a picture where the focus is at end of the hole. I just don't think that plunger is making a good seal so it's always bleeding oil at any pressure.

Thu Jul 10, 2025 4:01 pm

have you load tested the bypass spring,did you put the spacers washers between the cooler and it's mount when you replaced it,doing so gives the seals the correct amount of crush,and there are several styles of seals.

Fri Jul 11, 2025 12:34 pm

We hope you meant 32*btdc at @3000 rpm.

Fri Jul 11, 2025 3:27 pm

this may be of interest, credit to Amskeptic
https://www.itinerant-air-cooled.com/viewtopic.php?t=12422

Fri Jul 11, 2025 6:08 pm

Ok......let's clean up a few things here. I have only been paying about half attention to this thread because there are plenty of smart people here answering.

But you have too many "half known" issues here.

1. The twin VDO oil pressure units have notorious issues. Some work great and some don't. They also have more than one switch tolerance available etc.
You can buy a simple $8 water pressure gauge at Home Depot and connect it to the port and put to rest whether your VDO is accurate and what your pressure is at any given rpm and temp.

2. Put a 10/40 oil in it. For now.
I have seen very few stock 1.7, 1.8 or 2.0 that needed 20/50.
And the reason for this as well....

3. What oil pump does this engine have in it? Stock Type 4 or a type 1 pump? If it's a type 1 based pump and it's not one of say...CB performance units made for type 4.....it likely has a 30mm gear set. Way too big. Bigger gears along with thicker oil mean at certain rpms....pressure too high and cooler gets bypassed.

4. What is your engine code? Is this by chance an earlier case with the oil control valve under #1 cylinder? And/or did it have a mechanical fuel pump at one time? Look for a block off plate on the passenger side lower corner.

Ray

Sat Jul 12, 2025 5:13 am

Also check the bore for the oil relief valve, if it has worn or been gouged on the ID it will always be bypassing some oil even when closed. Causes the system to act funny. Also check the other oil pressure valve in the case and the bypass on the filter housing.

Sat Jul 12, 2025 7:11 am

Get a long thermometer and when the engine is at running temp shut it off and put the thermometer in the dipstick hole and get an actual oil temperature. When I put auxiliary coolers in type 4’s I get rid of the OEM cooler and just use the auxiliary with an electric fan and thermostat switch. Try using straight 30 weight oil and see if that makes a difference. Make sure the timing isn’t way out also. This is a good start